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Chris Brennen

Christopher Brennen

Richard L. and Dorothy M. Hayman Professor of Mechanical Engineering, Emeritus

By David Zierler, Director of the Caltech Heritage Project

September 26, October 5, 13, 17, 24, 2023

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Tuesday, September 26th, 2023. I am very delighted to be here with Professor Christopher E. Brennen. Chris, it's wonderful to be with you. Thank you so much for joining me today.

CHRIS BRENNEN: My pleasure, David. Thank you.

ZIERLER: To start, would you please tell me your title and affiliation at Caltech?

BRENNEN: Professor of Mechanical Engineering, Emeritus.

ZIERLER: You had a named chair in honor of Richard and Dorothy Hayman.

BRENNEN: Yes, I had the named chair. You'll have to forgive me, because from time to time, I have these mental blocks. You know it better than I do, so why don't you tell me what my title was?

ZIERLER: [laughs] It's the Richard L. and Dorothy M. Hayman Professor of Mechanical Engineering, Emeritus.

BRENNEN: That's correct. That's absolutely correct.

ZIERLER: Did you know the Haymans? Who were the Haymans?

BRENNEN: No, I didn't, really. I had very limited interaction with them. I had that chair before I retired. I inherited it from a series of eminent colleagues who preceded me. I had only very brief contact with the Haymans. To be honest, I can't recall much about them.

ZIERLER: With your title, Professor of Mechanical Engineering, is mechanical engineer the best way to describe what you've worked on in your career, what your interests are?

BRENNEN: I think so. Many people would have different interpretations of what a mechanical engineer is. I was really a student of engineering science, if you like, which is a little more of an esoteric subject dealing with the modeling and prediction of mechanical engineering procedures and devices. So, that's a little more specific.

ZIERLER: We can delve into that, perhaps, with some of the research questions you've pursued over the course of your career. What have been some of the big research projects you've worked on?

BRENNEN: I really worked on three major projects during my career. One was on the fluid mechanics of unsteady flows, in particular unsteady flows that occur in turbomachines—pumps, propellers, and so on—and specifically on cavitation. Cavitation is the process by which vapor bubbles form in a flow, a liquid flow, when the pressure falls below the vapor pressure. These bubbles, when they occur at normal temperatures, often collapse with great violence, causing damage to whatever surfaces or objects might occur near to them. This can detrimental as on a ship's propeller, but it can also be put to use, for example to clean your teeth. There's a device called a Cavitron, and the "cavi" there refers to the phenomenon of cavitation, and the bubbles that it generates next to your teeth clean your teeth. It is used in many other cleaning devices. It's also used increasingly in numerous biomedical procedures. Cavitation and unsteady flows were really my first and foremost subject of study. But I also worked on quite a different area, on the swimming of microscopic animals—bacteria, algae, et cetera, et cetera. That was a subject of great interest to one of my superiors, Professor Ted Wu, and at the time that we became involved in it, it was a somewhat controversial subject. What was really not known until we got involved was how exactly bacteria swim. Obviously that is of some relevance to humankind. Finally, coming back to flows, I was very much involved in the beginning of the study of the flow of granular materials—if you like, sand. We did lots of experiments in the lab on the flow of sand, trying to understand how sand flows. Those are, I would say, the dominant subjects that I studied during my career at Caltech.

ZIERLER: The term "engineering science," is that to say that your work really is a blend between building things and understanding systems on the engineering side, and really just trying to understand how nature works on the science side? Is that fair to say?

BRENNEN: It is very fair to say, put better than I could, I think, David. Yes. It derives from a history of quite eminent scientists who took a more mathematical approach to engineering problems. Model it, and then you can predict things better. That's how engineering science could be defined.

ZIERLER: Because Caltech is such an institution geared toward fundamental research, is that to say that maybe the option of mechanical engineering, the division of EAS, is it more scientific just by virtue of being within Caltech?

BRENNEN: I think the answer to that question is yes. Many of my predecessors began, as I did, basically as applied mathematicians, who learned a set of skills, a set of mathematical skills, that were applicable, if you like, in ordinary mechanical devices. So it was really the subject of mathematics that allowed me to make what success I had in the area of those subjects that I referred to.

ZIERLER: You alluded to it in explaining so nicely the three main areas of research in your career—cavitation, swimming of microscopic animals, flow of granular materials. Where in that research were your motivations really purely basic science and fundamental, and where did you see opportunity for what we now called translation, to societal benefit either with companies, or technologies, or tech transfer, things like that? I wonder if you could speak to that.

BRENNEN: Yes. The subject of cavitation was one which was clearly of importance in very practical circumstances. I'll just quote one example, because it is pertinent to my own history and why I'm at Caltech, and that is the subject of the cavitation of a propeller. That, as you may know from the movie The Hunt for Red October, allowed us to track the Russian submarines. It was understanding the relationship between the flow, the cavitation, and the sound that it produces—that's the key—that allowed us not only to track Russian submarines, but also to be able to know which Russian submarine we were tracking. That was because the Russians were not able to machine their propellers with the kind of accuracy that we were in the United States. The goal was to connect the specific roughnesses on a particular propeller to the sound that it made, and therefore the sound that could be tracked.

ZIERLER: Coming from an applied math perspective, I wonder what theorems or equations or even mathematical perspective stayed with you and informed how you approached the research in your career?

BRENNEN: A large branch of applied mathematics, particularly the applied mathematics of partial differential equations, which govern a large part of the fluid mechanics and the acoustics of flows. The odd thing I will relay to you is that when I look back at what I learnt over my years of education, I learnt most of that in high school!

ZIERLER: [laughs] The fundamentals!

BRENNEN: Yeah, I really did, and that was thanks to a truly remarkable teacher in this little provincial town where I grew up in Northern Ireland. We're going to talk about that, I think, later.

ZIERLER: Yes. Chris, have you been enjoying a true retirement? Are you still keeping up with the literature? Are you connected with colleagues?

BRENNEN: I did for quite a few years. In more recent years, the answer is no. I suppose that the memory is what limits me on what I can do now, as has been probably evident previously in this interview, and will probably occur again. There was a time when I had a phenomenal memory of process, of mathematics, and of phenomena. That was a huge help in knowing how to do something new. You could extract from this large library of knowledge pieces of mathematical tools that could be applied to the new problem or the new aspect of the phenomena that you're researching.

ZIERLER: Are you connected still with Caltech? Do you visit campus, ever? Do you stay in touch with colleagues?

BRENNEN: I do, but only on a fairly superficial level, I will be honest. I take great pride in some of the young faculty that I attracted and was able to recruit for Caltech. I wasn't solely responsible, of course, but responsible to a substantial degree in bringing young people to the faculty at Caltech, people like the late David Goodwin, Tim Colonius, Melany Hunt, Guillaume Blanquart and others. I take pride in that. I often stay with Melany and Bruce when I'm in Pasadena, and that's always a delight. So, yes. My older colleagues, people who mentored me, if you like, are almost all gone, I'm afraid. As far as I know, Ted Wu, who brought me to Caltech in the first place, I think he's still alive! I'm embarrassed to say I don't know the answer to that.

ZIERLER: I'll find out.

BRENNEN: I was hoping maybe you could find out for me.

ZIERLER: Absolutely. A generational question, when did computers become really important for your research? When did they start to become an effective research tool?

BRENNEN: Oh, that's a great question! Because when I was an undergraduate, Oxford University acquired its first significant computer. It was called a Mercury Ferranti computer, and it was truly something that people would laugh at today. It was a huge machine with lots of flashing lights like in a movie. You fed the program in with five-hole ticker tape, which they used to use, and maybe still use, in the stock market. It's paper tape with five holes across, and the combination of holes denoted certain letters or numbers. I would feed this paper tape, huge rolls of it, into this Mercury Ferranti computer. I had gained the permission from Oxford University to learn to use this great old machine. It worked for about 15 minutes before crashing. I had to time it carefully and get my results typed out within 15 minutes, otherwise they were lost. Then I would feed the tape back in again. I did this work, which I will describe at some point, with huge piles of paper tape on the floor, literally going out into the hallway, and then feeding the tape back in to make more progress. That was my first experience with computers. Of course I had a connection with them prior to that, because I knew a little bit about Bletchley Hall and the decipherment of the codes that the Germans used to communicate technical information during the Second World War. One of my uncles actually worked on decoding the Japanese codes, and he had interested me in those codes. It didn't mean a lot to me then, I will admit.

The first year of my graduate work, I played with that Mercury Ferranti computer and tried to solve certain flow problems using that computer. Oxford University then decided they'd better step up, and they got an English Electric computer called a KDF9, which used eight-hole paper tape. [laughs] You might think, "Wow, what a technological improvement that was!" But it was quite a useful machine. It had a much better printer for printing out results, so I didn't have to print out the results on eight-hole tape. I printed them out on a massive great line-printer that wouldn't be anything you would dream of using in this day and age. Essentially, I did my PhD using that computer. When I had enough results to type up my thesis, I realized, since I had almost no money whatsoever, that instead of paying someone to type up my thesis, I could get this printer to print out my thesis. I think Oxford didn't know enough to be able to deny me that opportunity. I still have behind me on my shelf the PhD thesis—actually, they called it a DPhil thesis in Oxford—that I printed out using that KDF9 line-printer. I was able to print out multiple copies. I'm sure they wouldn't allow that today, but it was financially [laughs] advantageous to me back then.

ZIERLER: In the latter part of your career, as computers became more advanced, did you ever get involved in simulation of experiments?

BRENNEN: Oh, yes! All the time. That was a major factor in many of the things I did—simulation of flows, simulation of microorganism locomotion, simulation of cavitation. Yes, that was a fundamental part of what I did, as well as experimental simulation. Most important to realize is that the combination of simulations with experiments allowed you a much greater ability to understand the phenomenon you were looking at. If you could simulate it right alongside your experiment and then compare the two, you knew where the simulation was going wrong and where it needed to be improved. That was a major development in mechanical engineering during my time in the subject.

ZIERLER: Tell me about some of your graduate students and postdocs. I'm interested, in very rough proportions, who went on to academia, who went on to industry.

BRENNEN: I don't know that I have the numbers on hand. I had about 34 PhD students. A large number went into academia. I'd say that, oh, half of them went into academia, and half went into other areas, industrial or government labs. One of them—actually, two of them—I'll explain my uncertainty later. Garrett Reisman became a NASA astronaut and Bob Behnken, whom I jointly supervised with Richard Murray, so if you'd like to call him a half, also became a NASA astronaut. I'm very proud of both of them. They were also great friends, particularly Garrett Reisman. We did a lot of hiking and climbing together. Also canyoneering, which I helped pioneer in California. I am thought of as the father of the sport of canyoneering in California. But we'll talk about that sometime later.

ZIERLER: Let's talk about that right now. What is canyoneering, and what did you do to invent it in California?

BRENNEN: You bet. Well, we're going off on a substantial tangent.

ZIERLER: That's part of the fun.

BRENNEN: It is part of the fun. I had three great children, all of whom I tried to expose to the wilderness and to adventure. When they were quite young, we would venture up those marvelous canyons in the San Gabriel Mountains, up above Pasadena, and Sierra Madre. We would try to climb up waterfalls. My younger daughter tells the story, with great glee, of hanging on the end of a rope—which she should never have done, of course—while we were trying to climb up a particular waterfall. As that went on, I had some graduate students who were very interested, and we'd venture further into these canyons. Some of them are really precipitous - really rugged. It naturally occurred to us, "Well, why don't we try to come down from the top? We can't climb up this waterfall or that waterfall, just can't get up, so we'll come down from the top." In particular Garrett had some experience with rock climbing by ropes, and using ropes, and so we started to descend the canyons of the San Gabriels – later venturing further afield to places like the Grand Canyon. Death Valley which was a great favorite of ours. We'd go there and we'd descend those desolate canyons, taking up to eight or nine hours for a descent. I wrote up almost all of those stories on my website, and those descriptions are now widely used guides to canyoneering in the West, and in fact in other places in the world.

Canyoneering is getting into a canyon, high up, with equipment, and rappelling down the falls, dry or wet, that you encounter in trying to descend. A big key to that is being able to make safe—very safe—anchors at the top of each of these rappels, with which to use to descend. There, my mechanical engineering ability I think played a role, because you had to be able to assess, with great confidence, that an anchor was safe to use to hold the rope at the top. That's canyoneering. I had enormous fun with it. I made a great many friends. Garrett likes to think that his stories of canyoneering helped him be chosen as an astronaut. I'm not sure I know that for sure, but what I do know for sure is that the next year, when Bob Behnken applied to be an astronaut—and Bob went on to be head of the Astronaut Corps, as you may know—he told the story about learning to canyoneer from Garrett and I, and told it with a sense of humor which made fun of Garrett and Garrett's particular instruction as to how to rappel. Then, when they went up on their first voyage in the space shuttle, voyage to the space station, they went up together. I have another personal story to tell on that later. They went up together, and it was amusing because Bob had to get on the end of this arm to go and do some fixing of the space station, and the person in control of that arm was Garrett, and so he had lots of jokes about whether Bob could be sure of Garrett's ability to guide him properly through space. I'm giving a short version of the story.

ZIERLER: Was canyoneering always a hobby for you? Did you ever see any opportunity to integrate it into your research?

BRENNEN: I'd say no, but I did write a paper on the dangers of canyoneering. There was a discussion that came up at some point among my professional canyoneering friends about the dangers, and what was the most dangerous thing, so I wrote a paper on what kind of force a person on the end of a rope would be subjected to in a waterfall. I also embarked on other adventures, such as descending the length of the Grand Canyon in an inflatable raft. Those are parts of my history that we'll come back to from time to time, because it was a large part of my life. In my youth I was quite an introverted young man and these experiences allowed me to get beyond that introversion and make great friends. At Caltech I taught David Wales, for example, to rappel, and he went with me on quite a number of these adventures. There were other of my graduate students who went along as well—Doug Hart, who became a professor at MIT; Clancy Rowley, who became a professor at Princeton. We would talk about their studies and about scientific subjects while we were on those eight-, nine-hour descents of canyons.

ZIERLER: A question about how you see your national identity. Have you been in this country long enough where you basically think of yourself as an American? Or between your family connections and even your accent, do you still feel connected to the old country?

BRENNEN: That's a good question, and a slightly complicated question to answer. Of course I regard myself as American. I became a citizen as soon as I could, because of the need to do so, because of my security clearance, which we may well come back to at some point. So, I am American, and all of my loyalties are to this country. But there's a piece of me too, deep down, that is very Irish. I say Irish, I don't say English, even though I owe part of my education to the English. I was more at home in the USA, especially in the Western United States, than I ever was in England.

ZIERLER: For those who have a really good ear for accents, could they guess where you're from, do you think?

BRENNEN: They should be able to, yes. I have the remnants of a Northern Irish accent. Some people think I'm Canadian, and the reason for that is that during the emigration of the Northern Irish to North America, they went to two destinations predominantly—not to Boston and New York; that was the later Southern Irish immigration—they went to Toronto and they went to Philadelphia. Those were the two venues for the Northern Irish. And they left traces of their home in the accents of those cities. Of course, the Northern Irish played substantial roles in the foundation of the United States. I can't remember exactly, but there is a saying among the Northern Irish that descendants of the Northern Irish wrote out the Declaration of Independence, or first printed it, first announced it. The Northern Irish also played a huge role in the military history of the United States, everyone from Davy Crockett, Jim Bowie and Sam Houston to Stonewall Jackson and Ulysses S. Grant. These are all people who are remembered in the homeland, in Northern Ireland. I don't want to draw too much of a line between the Northern Irish and the Southern Irish, because there's a lot of mixing within Ireland. I feel primarily Northern Irish, but then also Irish, in particular because some of my ancestors came from Southern Ireland, as you can tell from my name, which is a common Irish name.

ZIERLER: Do you still have family in Northern Ireland? Do you visit?

BRENNEN: I haven't visited in a while. I do have two brothers who still live in Northern Ireland. I had a sister also, but she passed away. Then I have the family of my first wife, whom I'll talk a little bit about, if you wish. And, my second wife, Barbara, who comes from the same village that I came from in Northern Ireland, and more about that later.

ZIERLER: Tell me about your decision to relocate away from California after you retired.

BRENNEN: Oh, that's also a good question. It was one taken with some hesitation, I have to say. I really enjoyed Caltech immensely, and I do miss that connection. But I suffered, as you may know already, two substantial tragedies that really changed my life. My son was killed in an automobile accident [Brennen pauses as he becomes emotional] and my first wife never recovered from that tragedy. I guess I didn't really, either, though I had to go on for the sake of my daughters. My first wife about ten years after my son, I think primarily because of my son's death. I then had the great, great joy of making acquaintance again with a girl that I grew up with in our home village. I knew her in kindergarten. A little over a year after my first wife died, we were married on a beach in Mexico with all of our family present. But going back to the question, I still retain substantial contacts with—my first wife's name was Doreen, so let me call her that—with Doreen's family. They're also part of my family. Most of them live in Northern Ireland, so I have a lot of connections still, not just biological but also through my first wife.

ZIERLER: If you're comfortable talking about it, if it would be good for you, tell me a little bit about the tragedy in which your son lost his life. What happened?

BRENNEN: Oh, boy. Yeah, I'll try to tell you a little bit, but I—it is hard. He was killed on New York Drive, just a few hundred yards from where we lived in Sierra Madre. He was a bit like me when I was young; he was a bit of a daredevil, if you like. He was killed in a single automobile crash in the middle of the night, in the early hours of the morning, on New York Drive, when he lost control of his car and slammed into a lamppost.

ZIERLER: What was your son's name?

BRENNEN: Patrick. Patrick Brennen. That was a very, very tough—I had to go identify the body and other terrible things. I don't know that I can say much more than that.

ZIERLER: I'm so sorry.

BRENNEN: I think he just—he went beyond his—I mean, there was really no other details to it. He lost control of his car, and that was it. It was an awful, awful—and in some senses, I managed to survive that for a while. Then when my first wife Doreen died, of cancer, I was really completely emotionally destroyed by that. The fact that I had been unable—one of the things about Patrick's car was he had lowered it down. It was the style of the times. He had lowered his car down—he was 23 years old when he died—low to the ground, and that's what caused the car to go out of control. I knew that I should have told him that he was liable to lose control if the chassis touched the ground, but I didn't tell him that, and it was too late.

ZIERLER: Were your colleagues supportive? Was Caltech supportive as you were in grief?

BRENNEN: Oh, yeah, they were. People like Bob Grubbs, who was a great friend. The Grubbses, both Helen and Bob, were great friends. They helped a lot. But also people like Melany and Tim [Hunt]. Caltech was very helpful in giving me time and space to recover.

ZIERLER: Between your son and your wife and those tragedies, when it was time for you to retire, was it easier for you to leave California, to emotionally separate yourself to some degree?

BRENNEN: No, I don't think so. I don't think that was a factor. I still love the mountains. I love the desert. I love Caltech. That was not a factor in my deciding to retire.

ZIERLER: Let's go back, now. Let's establish some personal history. How many generations does your family go back in Northern Ireland? How far back can you trace the lineage?

BRENNEN: At one point in my life I did substantial genealogy research, which was great fun. I spent many fascinating hours tracking my ancestors. However, the furthest back I could go was the mid 1700s, and the reason is that the Irish records—the church records—were very poorly kept or maintained compared with the English records, for example. It's very hard to track your ancestors back beyond about 1750 in Ireland. But I was able to go back, in some instances, to the early 1700s. They came from both Northern and Southern Ireland. I think I inherited some academic inclination from both of my grandfathers and from my grandmothers, too. My paternal great-grandfather and grandmother were schoolteachers. He was born in Southern Ireland and made his way north to get away from various troubles and find a teaching position in Northern Ireland. My maternal grandfather was even more successful academically. He also came from a very poor background and got a teaching certificate. He became a school teacher and then became a faculty member at the Belfast College of Technology. He in fact became the president of the Belfast College of Technology. Regrettably, he died of an appendectomy when he was quite young. More about that in a moment.

My father came from a very humble background in the backstreets of Belfast, the grimy, industrial backstreets of Belfast, places where the people who built the Titanic or worked on the linen mills lived. It's a much nicer city today than it was then. Through dint of great application, my father got to university—Queen's University Belfast—and became a doctor, and ended up as the chief surgeon, and for many years the only surgeon, at this rural hospital in the village of Magherafelt—that's the village where Barbara and I both grew up. There he was invited to come and set up a new hospital at the end of the Second World War. He really advanced because of his parents' determination that he focus on his education. My mother, because of her father's death, was in a different situation. My mother lost both of her parents while she was a teenager, which left its mark on her. She met my father at Queen's University in Belfast.

ZIERLER: What were your parents' experiences during World War II?

BRENNEN: Good question, because that really follows on from the last question. I was born, of course, right in the heart of the Second World War, December 3rd, 1941. So, four days before Pearl Harbor. I was born, in Belfast, in Northern Ireland. It was a tough time. My mother used to occasionally claim that I was born during a German air raid. I looked up the dates of the German air raids, and she wasn't exactly telling the truth, not specifically. Though, I believe her when she said that some of their phosphorous bombs bounced off the roof of our home into the roadway and burnt out there. I'm pretty sure she was telling the truth when she said that she and I had to hide under cast-iron tables that were issued to the population of Belfast so that they could hide under them in the event of an air raid—they were called Anderson tables. I've never really looked up the truth of that, but anyway. We were then evacuated—I have no recollection of this—we were evacuated to an uncle's farm in the countryside when I was just a couple of years old, but went back to Belfast when the War began to wind down, when the danger of the bombing began to decrease.

Then my father got offered this opportunity, as I think I've already said, of really setting up a hospital in this rural village, using, as a starting point, this old workhouse, this tumbled-down workhouse. I don't know whether you know anything about Irish workhouses, but during the Famine, and before, these were poorhouses that the government had built to try to take care of the numerous destitute population in the aftermath of the Famine and beyond. So, there's this ramshackle old building, which I remember, that my father was told he could use to create this hospital. And he did so! The hospital survived until about 20 years ago when finally they decided that they needed to centralize the hospitals of Northern Ireland, and the hospital was turned over as a care home, I think.

ZIERLER: Were there post-War deprivations that you remember in Northern Ireland?

BRENNEN: Oh, you bet! Fortunately, I had a number of uncles who were farmers and they would give us produce, eggs, vegetables, and so on, to make up for the deprivations. There were these coupons books that our parents were issued, and had to have a coupon, as well as the money, to buy many different items. But, as children, we were given some special items. We were given this orange juice, concentrated orange juice, and that was delicious. I loved that orange juice! We were given Kepler's malt, these big jars of malt. Barbara and I remember stealing some malt from my parents' pantry when we were very young. So, there were multiple deprivations. As they began to be relaxed in the late 1940s, I remember getting my first raincoat, for example, in order to travel to London on a special visit. It was the first time I had left Northern Ireland. I remember the shoes and the raincoat that was bought for me, something I didn't have before. So there were extensive deprivations, but I'm not sure they affected us very much. What was great about moving from Belfast—grimy Belfast—to this rural town—was that we had all these fields we could roam in, and quarries we could climb, and all kinds of adventures. When I look back, that's what I remember with greatest joy—making expeditions, and building rafts for the local rivers, and so on. The only thing that marred it, really, was the tribal hatred that had inflicted the country of Northern Ireland, the conflict between the Catholics and the Protestants. The village of Magherafelt lies on the border between the predominantly Catholic western part of Northern Ireland, and the predominantly Protestant eastern part of Northern Ireland. So, we were right in the middle of that confrontation.

The lessons of that hatred stayed with me, I think, throughout my life, and throughout Barbara's life as well. It taught us the terrible effects that these kinds of tribal hatreds could have on people and populations. Many of us couldn't wait to leave to get away from those, and yet we learnt from those experiences, too. We learnt how to try to counteract those hatreds. Sometimes I would tell some of the minority students at Caltech of those experiences, and how much it hurt when I experienced discrimination as a child. That extended over to England, to Oxford. I should say those experiences weren't limited to my time in Northern Ireland. They were also true at Oxford. Oxford had an underlying level of discrimination within it, within the English population. I was certainly discriminated because of my Northern Irish accent. I know that, for a fact. I went back at one point, from Caltech, to be interviewed for a job at Oxford. I know I was better than all the other applicants. Many years later, one of my friends admitted to me that my Northern Irish accent really frightened people and discouraged them from selecting me. Much to my later benefit, I will say, but it did hurt at the time.

ZIERLER: We'll come to all of that! When you were a kid, did your father involve you in his work? Did you get an up-close sense of science and medical engineering and things like that?

BRENNEN: And the answer is no. Actually, I was a little bit resentful of my father to be absolutely honest. Like many Irish fathers, it wasn't his job to worry about the children. It was his job to go and earn money and to make himself big and famous. And he was, for he did achieve some fame. My father won the OBE, which is an award that the Royal Family gives to people for their contributions to society. But he never came to my football games. He never went to my dramatic performances. I did a lot of theatrical work when I was in high school; he never came to those. So, I grew up and still have, as you can tell, some resentment to my father, for his seeming neglect. But it was true of all fathers in that culture at that time, and I came to understand that better as the years went on.

ZIERLER: It was benign neglect? He wasn't abusive or anything like that?

BRENNEN: No, no, he wasn't abusive. It was benign neglect. That's correct.

ZIERLER: Tell me about your mom. Did she work outside the home?

BRENNEN: No, she did not. One of the reasons for that—and this is another piece of me that we'll get to talk about. My sister, Paula, the youngest child in the family was born with Down's syndrome, and so my mother had a very difficult time, taking care of Paula. In fact, I spent a significant fraction of my years caring for her. Since I was the eldest boy, I spent a lot of time. I never regretted that, because I think, again, like the Catholic-Protestant conflict, caring for her gave me an understanding of what mattered, and what did not matter. [emotional] As you might detect, I still feel emotional about that. She died at the remarkable age of 63. We were told at the beginning she wouldn't live beyond 30. Well, she lived to 63. She outlived my mother and fortunately was taken care of by a family in my home village of Magherafelt for the years between my mother's death and her own death. A big part of my growing up, was the experience of what it was like to be mentally disabled. I don't know that they use that word anymore, but we thought of it that way.

ZIERLER: Were you always interested in science and engineering? Did you have chemistry sets when you were a kid? Did you like to build things and tinker?

BRENNEN: There were no chemistry sets in the aftermath of the Second World War, but I loved to tinker, yeah. What took the place of those were electric trains. My father had somehow inherited a very crude electric train, which didn't work, and he didn't really have the knowledge to fix it, so I tinkered with that to get it to work. I loved electrical things. I was quite young when I built my first audio amplifier out of vacuum tubes and other pieces of electronics. I loved working with bicycles. We built what we called carts. Even before bicycles, we built carts. These were made from the wheels of a child's pram. You know what a pram is? A perambulator, a baby carriage, if you will. We built those, and we raced them down hills, in the most outrageous kind of daredevil ways. There was a particular rhododendron bush that you could aim at, at the bottom of a lawn, and you could actually go right through, underneath the rhododendron bush. Part of my daredevil experiences growing up.

ZIERLER: Was your family religiously affiliated? Would you go to church on Sundays?

BRENNEN: Another good question. The answer is no. My father was not religious, and so unlike all the other children in the village, including Barbara, we were not required, not forced, to go to Sunday school or to church. My mother occasionally managed to clean us all up, but she had the responsibility of dealing with Paula, my sister, and so she didn't have much time for that either. So the answer is no. Unlike all the other children in the village, I was not required to go. I did occasionally go. When I got to teenage years I had an eye on my current wife even then, and she was going to this bible class, so I agreed to go because Barbara was there. I did, and it paid off, I guess, in the very long run.

ZIERLER: The village, what was the religious demographics? Was it mostly Protestant, mostly Catholic?

BRENNEN: It was about 50/50 because it was on this border between the predominantly Catholic and predominantly Protestant regions of Northern Ireland. There was a degree of tension between those communities. They would all go to their own churches. I always thought it was kind of ridiculous—and I speak here personally, obviously—that on Sunday they'd all troop off to pray at these different churches. If they'd just get rid of these damn churches, I thought to myself, maybe everyone would be a lot better off, and be able to get along. The one saving grace in that—and in response to your question—and I'll come back to the high school again—I went to this high school, the only high school in Magherafelt at that time, that was called the Rainey Endowed School. It was remarkable in several respects. First of all, it specialized in math and science. At least, the best teachers were in math and science. Secondly, it had both Protestants and Catholics there. And, it was co-education, which meant girls and boys. It was the only co-educational and mixed school in Northern Ireland at that time. So the teams that I played on, playing rugby or soccer, were a mix of Catholic and Protestants, and I made friends on those teams – friends that I still have to this day. That was a real saving grace in the context of that last question you asked.

ZIERLER: As the son of a surgeon, and because I know that generally in Europe, in England especially, class is something that people are really conscious of, what was your class status growing up? What would your family have called themselves or considered themselves?

BRENNEN: They were certainly professional. Upper middle class, they would have called themselves. Because my father was the local surgeon, the local doctor, he derived a lot of class from that. My mother had already come from a somewhat class-conscious background, growing up in Belfast. So, yeah, upper middle class. So were Barbara's family. Barbara's father was a local lawyer. I was the son of a local doctor. She was the daughter of a local lawyer. So, we were upper class. I remember questioning in my own mind, is this all correct? If I'm really honest, when I was younger, I probably looked down on the people who were of lower class, and of course quite wrongly so, but that's what kids do. They tend to imitate their parents' attitudes.

ZIERLER: Tell me about your schooling growing up, starting with primary school. Was it a small school, a large school?

BRENNEN: Primary school was tiny. It was the kindergarten school associated with the high school called the Rainey Endowed School. I remember about six or seven of us in kindergarten. The total population of the whole school right up through age 18 was probably of the order of 500.

ZIERLER: Was it a good school? Did you have a strong curriculum? You mentioned this wonderful teacher you had.

BRENNEN: Oh, yes, it was an excellent school. It really was. I don't know how they managed it—whoever had started the school really focused on trying to get the best teachers. The math teacher to whom I owe a great deal of gratitude was a man called Dr. Gwilliam. He actually had a PhD from Cambridge. He was Catholic, also. What was he doing in this little village in Northern Ireland? I never really understood that. I never had a chance to question him. But he sure was a great math teacher, and he taught me a great deal, and got me into Oxford because of that.

ZIERLER: Tell me about your interest in the dramatic arts. What kinds of shows did you do?

BRENNEN: All kinds of shows. It's in the Irish bloodstream, if you like!

ZIERLER: [laughs]

BRENNEN: I absolutely loved it! I wrote a little bit on my acting background for my autobiography, and I think one of the first shows I was in was at the age of—probably 13—was this little operetta that the school put on as part of a larger musical production. I think I had but one line in that. I was dressed up as the prime minister. One of the events of my life that I still look back on. While the others were talking, I marched onstage as the prime minister. I stuck my thumbs in the waistcoat that I had and jumped up and down just as Winston Churchill did. Somehow the audience absolutely loved that. They broke in huge peals of laughter, at this little shy little boy, with his fingers in his waistcoat armbands, jumping up and down, like Winston Churchill. That was my first theatrical experience and it stayed with me throughout my life. I played all kinds of parts, musicals and dramatic productions. I played Koko in The Mikado, the Gilbert and Sullivan musical. I played in various other dramatic productions. Later on, I realized that those experiences, of being able to project my voice, of presenting myself in public, was of tremendous value to me, later on in life. I would use those skills when I gave a talk. At first, when I gave science talks, I had to be a little careful not to try to give too much of a performance. That was not good for a science talk. But it did help me with the vocal skills and presentation skills. I also spent a lot of time on the rugby field. I was a very slim little boy, so I really took my lumps playing rugby! But I enjoyed that immensely, too.

ZIERLER: Chris, I want to set the stage for our next talk where we will pick up with your education at the University of Oxford. Just by way of context, I know that in the British system, you have to go in having a good idea of what you want to study, that you have to commit from the beginning?


ZIERLER: Is that to say that you were attracted to Oxford primarily because of science and engineering? Was that the draw for you?

BRENNEN: No, not really. I suppose to a minor extent. I went up to Oxford because it was obviously a way to improve myself, a new experience, perhaps giving me the opportunity for a career that I might not otherwise have been able to enjoy.

ZIERLER: Is that to say that you only got more interested or more focused at Oxford in science and engineering once you were there?

BRENNEN: Yeah, I think that's true. Yes, that's true. I've often said I really became interested in a subject only after I had started to commit myself to it. There's some truth to that.

ZIERLER: How competitive was admission to Oxford then? Would you have to have graduated at the top of your class?

BRENNEN: Pretty much, yeah. There was another very outstanding fellow student of mine at the high school I went to. His name was Derrick Crothers. He went on to be a professor at Queen's University Belfast. He was an exceptional mathematician. He was even better than I was at math. In the final high school exams in Northern Ireland, he came first in mathematics, and I came second. I always felt that there was a certain educational value in not being number one. Not being the number one sometimes has great advantages.

ZIERLER: [laughs] Finally, Chris, last question for today. Next time we'll talk more about the discrimination you experienced at Oxford. Did you know that going in? Did you know that coming from Northern Ireland you would expect these kinds of difficulties?

BRENNEN: No, I did not know that. That was a shock for me. As I mentioned earlier, it went on throughout my experiences at Oxford, and left me with a slightly bitter taste in my mind for Oxford, despite the fact that I loved it. There were tremendous experiences, both academically and socially. I'll tell you about one of those next time, because one of those benefits came when I visited the United States as a senior at Oxford, on a scholarship. That led ultimately to my emigration.

ZIERLER: I can't wait to hear it all, Chris. We'll start next time with your experiences at Oxford and we'll go from there.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Thursday, October 5th, 2023. It is wonderful to be back with Professor Christopher Brennen. Chris, it's wonderful to be with you again. Thank you so much.

BRENNEN: Thank you, David. Good to be here.

ZIERLER: We're going to start up where we left off last time, when you started as an undergraduate at Oxford. Before we get to some of the negative experiences that you felt, let's start with your perspective coming in. Between England and coming from Northern Ireland, what was the feeling of being somewhere close to home and far away from home all at the same time?

BRENNEN: I think it was almost all far away from home. First of all, the journey there was far greater than you might imagine today. I was left, by my parents, at the docks in Belfast, where I caught a ferry, overnight ferry, from Belfast to Liverpool. Then I had to find my way to the Liverpool train station. Lime Street Station was its name. The next day, I managed to find my way by rail from Liverpool to Oxford, with several stops, which were not familiar to me, because the railways had disappeared in Northern Ireland before I really got to the point of traveling very much. I arrived in Oxford—mind you, I had been there previously, for about four or five days, to take the scholarship exams earlier in that year, so I kind of knew my way around a little bit, but I was still very—frightened is the wrong word, but apprehensive, about finding my way to this strange college that I had been admitted to. My mother had mailed all my laundry, the sheets and other stuff, to the college, prior to my arrival. So I arrived there, and the first thing that was odd was this elderly gentleman at the front gate of Balliol College, Oxford, who addressed me as "sir". A strange thing for me to experience. Some of the things I had expected as a result of my earlier visit there.

I find myself in this austere Victorian room that hadn't been decorated for, oh, I would say maybe a century, prior to my arrival. But, I settled in. I arrived there before the other freshmen, because I had to take these other exams that were called prelim exams in Oxford, in order to qualify me to start my studies there. I didn't quite understand that. If they were giving me a scholarship, why did I need to take these other exams? However, they were relatively trivial exams in math, and physics, and chemistry—they didn't worry me. But I was there on my own for ten days. That was a lonely period, I remember. Then, suddenly, this horde of other freshmen arrived, and I began to make friends. I found them all very friendly and helpful. I signed up for various activities—for the rugby club, and for the dramatic society, activities which I knew from my time in high school. There it began.

I began to go to tutorials in the college. The Oxford system—and I think this is still true—consisted of two parallel streams of education. One was the tutorials you went to in the College, where you would visit with your tutor once a week, usually alone, and he would assign various reading, various homework problems and so on, which he would question you about the following week. On the other hand you also went into the university system, by going up to the Engineering Department laboratories for practicals and for lectures there, also. It was a strange system, but also a system that was quite elitist. My friends who attended the so-called red-brick universities didn't get that kind of personalized education.

After one term at Oxford, a new engineering professor came to Balliol College. His name was—and his name will feature in our future conversations—Les Woods. Leslie Woods. He was an eminent mathematician-engineer, and he knew a lot about subjects like fluid mechanics, thermodynamics, et cetera. But he knew absolutely nothing about some of the subjects I had to study—electrical machines and other such engineering devices. Right from the beginning, he and I hit it off, for several reasons. First of all, I was more inclined to the mathematics and basic physics than I was to the engineering and enjoyed those more. He also characterized himself as an outsider from the Oxford system. He had been born in New Zealand, and grew up on a beach in New Zealand, and by an incredible dint of scholarship and effort, he managed to find himself in this position of a professor at Oxford. But he was very much an outsider, and he relished the role of being an outsider amidst the somewhat stuffier other professors in the Engineering Department. So, that was my arrival in Oxford and the beginning of my studies there.

ZIERLER: Was it 1959 when you arrived at Oxford?

BRENNEN: 1960.

ZIERLER: How well-formed were your ideas about the kind of course of study you wanted to pursue? Did you have a pretty good idea from the beginning?

BRENNEN: I think so. Certainly philosophically. When I was applying to various universities for admission—I applied, for example, to the medical school at Queen's University in Belfast, and was admitted there. I also applied to the engineering school there. So, before I went to Oxford I had a big decision to make. Whether I would be more interested in engineering or in medicine. There was a lot of pressure to follow my father into the medical field, pressure that I finally and sensibly resisted, because my interests were much more in engineering and engineering-like subjects. That was a decision that I had already made, quite consciously. I had thought about it quite a bit and decided that I enjoyed machines rather than medicine. I had recognized the conversations around our family table, that while medicine was a very worthy profession, of course, that there wasn't really much science to it. It was all—and I'll use a rude phrase that I often used to Bobs Grubbs about chemistry—I would say, that's just suck-it-and-see science. [laughs] Where you just try things, and if they work, they work, and so suck-it-and-see science tended to be one of my remarks in talking to the more basic scientists. I opted for engineering.

I also liked machines a lot, as we described before. I liked trains, I liked the things that worked, and I liked trying to understand and see how they worked. I enjoyed cars and tinkering with cars, so there was a lot of that practical stuff that I had already found myself in, that encouraged me. But I could have gone to do mathematics. They admitted me to Balliol College on a mathematics scholarship. But I also made the decision before I got there that I wasn't really interested in basic mathematics, that I was more interested in applied mathematics. Those decisions, I had made before I got there. They weren't firm, but they were pretty firm by then.

ZIERLER: Coming from Northern Ireland, how much of an outsider did you feel relative to your other students? In other words, was almost everybody else from England? Were there other international students?

BRENNEN: There were other international students but most of my classmates were from England. A lot of them, of course, were from what they call the public schools, the elite schools of England, places like Eton and Harrow and Winchester and so on. I did feel somewhat the outsider amongst them. I had several experiences which—and I don't want to exaggerate them, but there was one occasion on which someone who obviously I'm not going to name, but a fellow student and I, who were very friendly, and he wanted to take me to his home for a long weekend at some point. He went to ask his parents whether he could bring this Northern Irishman home. For whatever reason they said, "No, please don't." There was a sense I felt that there was an antagonism against the Northern Irish, maybe against all Irish, in his somewhat elite family.

ZIERLER: For some broader context, what was happening in the late 1950s and early 1960s with regard to Northern Ireland, the U.K. and Ireland?

BRENNEN: There was a lot of terrorist activity, and of course that was a real problem in Northern Ireland at about that time. One of my friends in high school was blown apart by a car bomb. My first wife, Doreen—my first wife is Doreen and my second wife is Barbara. Doreen's cousin was assassinated by the IRA just about 20 miles from where I grew up. There were many bombs. You had to be very careful to drive anywhere at night because you would be stopped by the reserve police force. They were called the B-Specials in Northern Ireland. These were a force, created by the Northern Irish government, of volunteer policemen. They tended to be farm boys who were given weapons and told to go and do this patrol or whatnot. If you were stopped at night, you could find yourself rolling down your window and a machine gun would be put right in your face. That happened to me a number of times. That's scary! Especially since you know the guy behind the machine gun probably didn't have a clue how to use it. Those were frightening experiences, and they colored my early life there. I think there was a sense among people in Oxford—not so much my friends, but maybe among the tradespeople, that a Northern Irishman was fundamentally dangerous. That makes you feel very uncomfortable. My family had been threatened on a number of occasions. I remember once when an IRA gunman was shot by the police in my home village of Magherafelt, and my father had to operate on him and care for him in the local hospital. The police wanted to come and get this guy. My father was able to resist that. He said, "You have to wait until he's well, and then you can come and interview him, if you wish." Whatever happened to that gunman, I don't know.

ZIERLER: How did some of these tensions translate on a personal level to your experiences at Oxford?

BRENNEN: I think I've already said, there was a sense, when you first met people, that being Northern Irish you might be quite dangerous. Other than that, it didn't—there's another aspect to those troubles in Ireland and in Northern Ireland, and it's valuable to mention, because it had more of a role of my interactions with other people in Oxford and later, of course, at Caltech and elsewhere, in that I got a very early lesson on tribal discrimination, what harm that can do to a civilized society. The hatred and discrimination, blatant discrimination that occurred in my home village was something that was very clear to me, and which I came to really abhor in my childhood. Knowing that, my interactions with other people of any color or citizenship, that was something I knew I needed to resist and to try to counteract. That was a big part of my youthful experience.

I remember when I was dean at Caltech—it may seem odd to say this, but I had to deal with quite a few of the Black students who felt that they had been discriminated against by staff, maybe sometimes faculty. I could share the way I felt inside when I was discriminated against, whether in Ireland or in England, and I think that helped them. I hope it did. It certainly seemed to resonate with them, to know that I, as the dean, had also gone through the effects of discrimination and of how debilitating that can be to you as an individual. You feel lesser, you feel unable, you feel—it's a very debilitating feeling, being discriminated against, and I was able to tell them how I had experienced that and use that to help them at Caltech.

ZIERLER: On to happier subjects, once you had settled on engineering, as an undergraduate at Oxford what opportunities were there to specialize or gain exposure to the different areas of engineering—civil engineering, mechanical, aerospace?

BRENNEN: This was really engineering science. It was called engineering science, and that's because it was mostly the basic subjects of engineering science, of solid mechanics, fluid mechanics, thermodynamics, et cetera, et cetera. There wasn't much in the way of specialization. We were given a set syllabus. It was only a three-year course, so after three years, I took the final exams in all these subjects, from fluid mechanics, to applied mathematics, to solid mechanics, to thermodynamics, to surveying. We took a surveying course, too, which we had to pass. That was fun, because we roamed about the street, the countryside, around Oxford, and did our best to make sure our surveying line ran through the pubs that we knew of in the countryside. [laughs] I'm joking.

ZIERLER: [laughs] I'm curious if you thought about going the industry route or the professorial route as an undergraduate. When did you start to make those decisions?

BRENNEN: In the last year of my studies as an undergraduate in Oxford, I didn't know how well I would do in the final examinations. There was really no way to know how I would compare with my fellow students. And so, in my last year, I did what all of my fellow students were doing in engineering, and that was, I interviewed for various industrial jobs and learned a little bit about what they would involve. I couldn't find any of those too interesting, to be honest with you. I had no basis for knowing that I would do well in final examinations, but I was hoping to do well enough to be able to continue on into graduate studies. There were a lot of things that interested me—the space program. There is one other piece to this that I should interject before you go on. Because, at the end of my last year—that is, in June of my last year and before I took the final exams—I applied for and was awarded a remarkable travel scholarship. It was a scholarship that was set up by an alumnus which invited us to come to the United States for two or three months in the summer and travel around investigating in some particular personal interest in the United States. It was a fantastic experience. one that really changed my perspective.

Let me take a moment or two to express how it changed my perspective. We were given a list of names of former holders of these scholarships and other friends and alumni who were willing to put us up or have us to dinner. This list of names were from all over the United States, from East Coast to West Coast. We were also given a rental car, to travel in, as we went from one of these hosts to another. So, I traveled around, with another of the scholarship winners, a guy called Tommy Cookson. He was a public school boy and behaved like it, but he became a very good friend. Tommy and I still interact and talk on the phone. Tommy and I drove this rental car all the way around the United States. This was in the summer, immediately after my exams, but before I knew how I had done in the exams, and before I really knew where I was going the next year. We had some remarkable experiences, which are probably outside the scope of your interest, but we started off in Boston, Massachusetts. The man who had set up this scholarship was an alumnus by the name of William Appleton Coolidge. He was a Coolidge from that family, rather a distant guy, but he seemed to enjoy having set up this scholarship and helping these young men broaden their perspectives by visiting the United States.

We went from Boston down to New York, spent some time in New York. We made our way down to Washington. Now, this is the year 1963. The civil rights hearings were being held in Washington, D.C. I managed to find myself invited to be with a man called Nicholas Katzenbach—Nicholas was the—I might get this a little bit wrong—he was the Deputy Attorney General of the United States at the time. He welcomed us, and he arranged for us to get into the civil rights hearings, where I experienced the debate with people like-who was that South Carolina senator-whom I saw talk.

ZIERLER: Strom Thurmond?

BRENNEN: Strom Thurmond. I saw Strom Thurmond give his talk, in the Senate hearing room, against the civil rights bill! And he was questioning one of the Roosevelts at the time. It was an extraordinary experience, to be there at that time. We spent a number of days in Washington. Then we traveled on, down through Atlanta, stayed there, down to New Orleans, across into Texas, into New Mexico and Arizona. I won't detail all the stops because it's beyond what you were interested in, but I did go and work at a real ranch, in New Mexico, herding cattle. I had my one and only experience of throwing a small cow to the ground prior to its being emasculated and having other things done to it. I rode in the roundup prior to that branding. Later we ended up in California. I'm going on too long, but a few more little things here.

ZIERLER: Please!

BRENNEN: We did end up in California. Not end up; we stopped in California. One of the people we visited was a man who worked at the Union Oil Research, somewhere in the L.A. area. I don't remember exactly where. That was interesting, too. I was quite interested in that, practical things. We didn't go to Caltech. Then we went up the coast a little ways, where we stayed with the Sedgewick family near Santa Barbara—do you remember Andy Warhol, the painter?

ZIERLER: Of course!

BRENNEN: His girlfriend Edie Sedgweick. We stayed with her family, who were completely crazy. The father was a commercial sculptor, and most of the family committed suicide. That was a bizarre experience. Then we went up the coast, stayed in San Francisco, and then took the train back across the country to Chicago, where we stayed first of all, in Chicago, with an owner of a big chemical company, a big industrial capitalist. The next stop, which was Detroit, we stayed with a trade union organizer, so that was quite a contrast. And finally, back to Boston. There were just a raft of special experiences and opinions that I was exposed to during that visit. At the end of that, I found I had gotten a first-class honors degree at Oxford! Much to my parents' absolute astonishment, and my former high school classmates.

ZIERLER: Did that experience, that trip in America, plant a seed, do you think?

BRENNEN: Oh, absolutely.

ZIERLER: Did that make you want to perhaps pursue a life in the United States?

BRENNEN: Absolutely. Absolutely! Especially in the West. I loved the mountains and the desert. I loved the openness of the people. I felt far more at home there among the people than I ever did in England. That continued on into my later life in the United States. It was a place where the society was much more like that that I had grown up in, in Ireland than it was like the English. That was something that I said to myself—"If I get the opportunity, I'm going to go to the United States."

ZIERLER: As an undergraduate, did you ever hear the use of the word "computer"?

BRENNEN: Yes, I did. Oh, yes. I knew a bit about it, just a little bit. Because one of my uncles worked at Bletchley on the enigma machine. Turing and others invented computers to decipher messages sent by the German and Japanese enigma machines. I was also aware of Turing both for his computer work for the awful way he was treated by the British government. And that really appalled me.

ZIERLER: Graduating with first-class honors, first of all, what does that mean? What exactly is the academic achievement for you?

BRENNEN: I think there were about 70 students in my engineering class in Oxford, and there were, I think, seven of us who got first-class honors degrees. so first-class honors degrees were unusual. Most people got second- or third-class degrees, and the occasional person got a fourth-class degree, which is pretty much like failing. So, it meant a lot in terms of allowing me to recognize, I suppose, that I had some special abilities which were above the norm. Not that I ever quite believed that that made me special in any way. Because of the other experiences that I've just talked about, about discrimination and so on, I recognized that I wasn't particularly special, other than I did have a special power up here, to do mathematics in particular.

ZIERLER: This honor, is that what allowed you to stay at Oxford for graduate school?

BRENNEN: Yes, pretty much, that's correct.

ZIERLER: Did you give consideration to other programs, or did you want to stay at Oxford?

BRENNEN: I think I wanted to stay there. The tradition at English universities is very different from the tradition in American universities today where you typically would go to another university for your post-graduate work. The tradition in England was that you would continue on in the same university for graduate work. Since I hadn't been very excited about the industrial jobs that I was considered for, I thought, "This is what I want to do."

ZIERLER: Obviously in graduate school, this is the time to specialize. What were your options? What were your interests?

BRENNEN: I mentioned my tutor in Balliol, Les Woods. I guess he encouraged me to think about fluid mechanics or the subjects associated with fluid mechanics. I did that, and I thought some of the things were very interesting. He had some ideas for research that I thought were really quite interesting. Most of them focused on cavitation, and we'll come to that in a little bit. He encouraged me to stay on and do a PhD—or DPhil, in Oxford University—a DPhil, under his guidance. That worked out very well for me, I think. Though slightly eccentric, he was a very clever man, especially in his mathematics. He wasn't as good at the practical things, like doing experiments for example. He had the wisdom to realize that it might be a good idea for me to spend six weeks one summer at a place called the National Physical Laboratory, a research lab down in London, to work on various experimental projects related to my PhD. I did that, and that turned out to be very valuable.

ZIERLER: What was Woods known for? What was his most prominent research?

BRENNEN: He was known initially for fluid mechanics. He wrote a big, fat book The Theory of Subsonic Plane Flow. It was highly mathematical. Not very good from an engineering point of view. He didn't quote much in the way of experimental results. It was a very sophisticated kind of mathematics that was used to solve a certain class of fluid flows. There had been, in the 1940s and the 1950s, an explosion of mathematicians interested in these methodologies, the methodologies of solving plane incompressible flows, using devices that were primarily invented by Russian mathematicians, people like Muskhelishvili and Sedov and so on. Woods had also contributed to that. His book is highly mathematical in places. It was quite an effort for me to plow my way through that book, but it was very interesting to do so. Another person who was in that group of international scholars interested in those kinds of mathematical methods for flows was the man who I ultimately came to Caltech to work for, Professor Theodore Y. Wu. Ted Wu. We'll come back to him in the not-too-distant future.

ZIERLER: From the perspective provided by Woods, is that to say that your graduate experience was more theoretical than experimental?

BRENNEN: It was, but I was also interested in experiments and practical things. That's where my summer research studentship at the National Physical Laboratory was extremely useful, because I had the opportunity there to perform experiments, to learn under another man from whom I learned a lot, Dr. George Gadd, who was an experimental fluid mechanicist. I learnt from him how to go about various measurements, to do experiments, and ultimately how to do experiments in a huge, great facility that they had built in this lab and was essentially, at the time, being unused. It was too big, too expensive to make propellers and other devices to install in this water tunnel. We'll come back to that. That's getting off the right timeline here.

So, at Oxford I set off on my PhD work, which was mostly using computer programs to solve a particular kind of flow—free streamline flows, of which an example is cavitating flows. Those occur when a flow in water or any other liquid past an object creates such a low pressure in the wake of the object that the water or other liquid vaporizes, and so you get a wake that's filled with the vapor of the liquid. During my time both on the scholarship and later on at the National Physical Laboratory, I created small scale experiments that enabled me to examine such flows. That was great experience. George Gadd, whose name I mentioned, was really an excellent mentor. I learnt from him how to plan and conduct experiments from him, which was a tremendously useful addition to my education, but also one that I enjoyed. I enjoyed creating the hardware and the instrumentation and making the measurements and seeing how the measurements related to my theoretical work.

ZIERLER: Being an engineering graduate student in the mid and early 1960s, with the Space Race on, Kennedy announcing putting a man on the Moon by the end of the decade, did that register with you? Did that give a greater sense of what was possible in engineering?

BRENNEN: Big time. Big time. My dream would have been to have been invited to come and work at NASA, but it seemed almost impossible for this little Irish boy to get that kind of opportunity. But, yes, absolutely. The Space Race, wow.

ZIERLER: When you talk about computer programs, is this Fortran, punch cards?

BRENNEN: No, not initially, it wasn't. Fortran—initially, I think I described last time—the first computer that Oxford University bought was a computer called a Mercury Ferranti computer. I think I am repeating myself, but nevertheless. It was one of these things like out of the science fiction, with all these lights flashing, and you had to do this, and all—and you fed in five-hole paper tape, which was ticker tape, on which you had written the program in five-hole-tape language, in a simple language called Autocode. Not too different from modern Basic. Then, after it crashed, you fed the restarting tape into the computer and, if you were lucky, it ran without any mishap for another 15 minutes. I have obtained special permission to stay up overnight, after the staff that ran this computer had gone home, to run this computer myself, for 12 hours until the next morning when the staff would show up again and I would go home to get some sleep. There were quite a few nights when I got that opportunity. I tried to make the most of it, but it was hard.

I guess around about my second year as a graduate student, Oxford University bought another computer. It was an English Electric KDF9. It was marginally better. It was better in the sense that it used eight-hole tape rather than five-hole punch tape. It also printed the results out on this great, big line printer, like modern printers but about five times bigger. I think I mentioned the last time, when it came time to write my thesis, I also took advantage of this printer, because I had learned how to use it, to print out my thesis, and it saved me quite a bit of money. I could print out as many copies of my thesis as I wanted, and one of those is behind me on the shelf.

ZIERLER: Oh! [laughs] What was the basic research question that animated your thesis research?

BRENNEN: No one really understood what happened when a flow around a body created these vapor wakes, if you like, and what size they were, and what they depended on, and what were the dynamics of these large-scale cavities. So, I devised a numerical method to solve those flows, so that you could explore what the basic properties of those flows were. That's what I did for my thesis. I wrote a thesis on the calculation of free streamline flows using a computer.

ZIERLER: What were your conclusions? What did you see as your contributions to the field with this research?

BRENNEN: I don't think they were earthshaking, but they gave me a start. Many subjects in science, you develop a tool. I realized that I had the ability, or learnt the ability, to write programs for unusual fluid flows, like these cavitating flows, to be able to solve them, to understand them, as a result. That's basically what I did. My conclusions were how to program, how to solve these flows, using numerical methods, using a computer.

In addition, during my time as a graduate student I did spend six weeks, as I said, down at the National Physical Laboratory, doing some experiments on these kinds of flows. Thus I was able to make comparisons with my own calculations. That was very valuable.

ZIERLER: What did you want to do at that point? What was available to you?

BRENNEN: Again, I hadn't really thought through exactly what I was going to do when I finished. It was such an effort. I was married by that time, and we had a child, and I was running out of money. It was desperation time. In fact, I prepared my thesis, did all the diagrams and the typing and everything, in about two weeks, because I had to, to get this whole thing done. So I stayed up—that was a scary experience—I stayed up all night for about five or six days, until I finally collapsed. I had a tendency to be very determined when it came to that kind of thing. Anyway, I got that done, but I hadn't really made a great effort to find a job after my doctorate. Fortunately, the National Physical Laboratory where I had conducted the experiments I mentioned previously, offered me a research fellowship and I took them up on it. It was fairly lowly paid, but we moved down to London, the outskirts of London, and I started in on my research fellowship.

ZIERLER: This was an Oxford program, the fellowship?

BRENNEN: No, this was a British government program, at this government lab, the National Physical Laboratory. More specifically, I was allowed to serve this fellowship in the Ship Division. The Ship Division, which was in the suburb of Feltham, right near London Airport, actually, right near Heathrow. You could in those days see it from the air when you were landing at Heathrow. That's where I had done that earlier student fellowship. They had some remarkable facilities, which I'll take a moment to describe. Water tunnels. Huge, great water tunnels. One of the largest water tunnels in the world. This shows you how the British government sometimes works. They had had a smaller water tunnel, which was only about 15 inches in diameter. You had 15 inches in which to put a model or device to test. This had been built to test ships' propellors for the British shipbuilding industry, which was of course at that point on the point of complete collapse and subsequent demise.

They then decided, the government and the folks who worked at this lab, that they needed a much larger tunnel, because they didn't really understand how to scale up what was happening with these propellers and the way they cavitated. They didn't always cavitate, but they could be made to cavitate. Each of the blades would have an attached cavity on it. They didn't know how to scale up the results they were finding in the smaller tunnel, and so they built this huge tunnel, which had a working section—which for air doesn't sound very large, but the working section for this large tunnel was about four feet in diameter. Doesn't sound much—but when you have four feet of water going past at 40 miles an hour, that is some momentum. A fairly awesome sight to experience. But they weren't using this larger tunnel because it had been so expensive to make model propellers to put in it. So I said, "Can I ?"—this was by the time I had gotten there—"Can I put some simple objects in there and take a look at the cavities, at this high speed, and this big scale?" I did that. Those were exciting experiments, because they didn't charge me anything for them! I got to play in this great big facility that was being unused! I mean, it was ridiculous. In the end, not too long after I went to the United States, that whole lab, under Maggie Thatcher's government cuts, was demolished. For me it had been an opening of great good fortune, and I took full advantage of it to perform experiments in that water tunnel. It gave me an exposure to propellers, which we'll come to in a little bit, and the cavitation of propeller blades.

Here I will digress for a moment, because—and I think this is something you will know, also—that there was tremendous interest then—and now—on the cavitation that would occur in the wakes of propeller blades of submarines in particular. We tracked—I'm jumping ahead a little bit, but this is for reference—we, the United States, tracked the Russian submarines by listening to the noise, and because the Russians didn't machine their propellers very carefully, they had idiosyncratic roughnesses that would cavitate in a certain way and would therefore produce a particular noise signal, so that when we put hydrophones on the floor of the Denmark Strait—that is between Iceland and Greenland—I'm talking about we, the United States—we could tell not only that a submarine was going past, but we knew which submarine was going past, because each of them produced a slightly different acoustic signal due to the cavitation. I'm jumping ahead a little bit, but that's why there was a lot of interest and focus on cavitation, on propeller cavitation.

While I was at that National Physical Laboratory, there were several Americans who came by to visit this lab. One of the visitors was Professor Ted Wu from Caltech. Ted came to visit some of his old friends there, not really specifically on cavitation. But he had several friends there, including George Gadd. I think he said to Ted, "Why don't you go see this young guy over in the cavitation lab, because you might be interested in some of the things he's doing?" Ted came over, and we spent a marvelous, oh, I'd say hour and a half or more together, while I told him about the research I had been doing there on cavitation, cavitating propellers and so on. He went away very interested in what I had done.

Then, about two weeks later, I greeted another visitor, from the U.S. Navy, who came by to talk to me specifically about what I was doing and what I was finding. A nice man, whom I subsequently had a lot of interaction with. Dr. Jack Hoyt was his name. Jack also seemed very interested. And—I'm just reading between the lines—I think when the two of them, Hoyt and Wu, got together shortly after those visits, that they arranged that I should come to Caltech and continue to work in the subjects that I was involved with. How that was arranged, I don't know, but in those days, those kinds of informal arrangements tended to govern the administration of science much more so I think than happens these days. About a month later, I got a letter from Ted Wu saying, "Would you like to come to Caltech on a research fellowship for a year?" He said, "We'll offer you a salary of $10,000 a year." Wow! That was three or four times what I was making, so that was a big exciting moment of my life.

ZIERLER: And, it gets you back to Western United States.

BRENNEN: It gets me back to the Western United States. Oh, I was so excited by that. I went on to get a Fulbright fellowship for the purpose of coming to the United States, also. That meant that after only about a year and a half at that lab, the National Physical Laboratory, we ended up packing up all our stuff and selling everything we could to pay for the airline tickets for my wife and myself and our child. Thus we emigrated to the United States. My mother, of course, thought she would never see me again. There was the classic Irish little playlet of the adventurous son saying goodbye to his mother. Mother was in floods of tears because she feared she would never see me again. Because this was part of Irish culture, that your best and brightest went off to seek their fortune in other lands!

ZIERLER: [laughs] I hope you proved her wrong.

BRENNEN: She lived to a very ripe old age. She will enter the picture again a little later, but yeah, she lived to the ripe old age of 92 or 93.

ZIERLER: If you're able, some background on the National Physical Laboratory in the U.K., what is its history? How far back does it go?

BRENNEN: I'm not sure I can answer that. I don't remember, exactly. But certainly it played a significant role in the wartime activities of the British government. Turing worked there. After the war Turing brought his computer from Bletchley to the National Physical Laboratory and set it up there. I remember seeing it. It was kind of a museum piece, of course, by the time I got there. And if you go and see that movie, what was it called, that featured Benedict Cumberbatch?

ZIERLER: I don't know the name, but I know the movie you're talking about.

BRENNEN: Anyway, Turing worked at the National Physical Laboratory. The lab also made some other marvelous contributions to the war. They invented radar there—I forget the years—and so on. They did a lot of basic scientific research. The National Physical Laboratory is still very much a going operation, though the Ship Division finally disappeared about the same time that the last vestiges of the British shipbuilding industry disappeared.

ZIERLER: Was NPL a center of cavitation research? Was that really the place to be?

BRENNEN: Yes. There was one other place called the National Engineering Lab up in Scotland, but that was more practical. NPL was the place to be, though, in my area of research.

ZIERLER: What aspects of your thesis research were relevant to your fellowship at NPL, and what was brand new for you?

BRENNEN: What was brand new for me at NPL was learning more advanced instrumentation, especially in high-speed photography. See, things happen so fast in these flows. Let me again take a moment on an aside to describe that. Cavitation can take a number of forms, and one form would often morph to another. It begins when the pressure in the wake, if you like, falls to a certain level, so that as the water vaporizes, the first manifestation of that is the creation of small bubbles, small vapor bubbles. Those bubbles, for a variety of reasons I won't go into precisely, tend to grow in a fairly controlled way. But then when the surrounding pressure gets above the vapor pressure again, they collapse, and they collapse enormously violently. They collapse with tremendous force. Unless there happens to be a trace of air in the bubble in addition to the vapor it creates enormous pressures and temperatures. Whatever is left in, whatever little bit of non-condensable gas is in there, gets so compressed that for a tiny instant, the temperature and pressure inside that bubble can be greater than the temperature of the Sun. It's a remarkable phenomenon. That is in part, or also of course, what creates the noise. The violence of the collapse of these bubbles is what creates the noise. That's one manifestation.

Later on, then, as you decrease the pressure further, those bubbles collapse into great big attached wakes behind objects, behind a propeller blade or whatever. In order to capture those dynamics of the small bubbles, the way they grow, the way they collapse, you could of course, as I did, measure the sound propagation from those little bubbles. That was part of the Hunt for Red October business. You really wanted also to photograph the process, but it happened so fast you needed a really high-speed camera. I got involved in trying to deploy very high-speed photographic techniques in order to capture what exactly happened to that little bubble as it collapsed so violently.

ZIERLER: Just to foreshadow to your later work in support of national security issues in the United States, did your work at NPL start that process?

BRENNEN: You bet. Oh, yes, I think so. Not that I had gotten very far in terms of the stuff that I ultimately ended up doing at Caltech and for the U.S. Navy, but yeah, it got its start. I knew what some of the fundamental issues and problems were by the time I came to the United States.

ZIERLER: You've already alluded to it a little bit, but because it's so important to Caltech and to how you got to Caltech, tell me a little bit more about what Ted Wu was working on that brought him into contact with you.

BRENNEN: Ted was working on the mathematical methods of solving these flows, not using computers. I mentioned earlier a class of applied mathematicians who had worked on these relatively simple geometric flows and solved them mathematically, using pure mathematics, as opposed to computers. He was in that class. He had done quite a bit. But he was very interested in what really happened in a cavitating flow, and what other devices and experiments you might do. That was what I guess brought us together.

ZIERLER: What was he like as a person?

BRENNEN: Oh, lovely man. I'm afraid I don't know whether he's dead or alive.

ZIERLER: I believe he's 99 years old. I believe he's still alive.

BRENNEN: Must be! My goodness! He is a marvelous man, and he gave me and others opportunities that we wouldn't otherwise have had. He also understood how discrimination can be soul-destroying. His experiences in China and elsewhere made him a man that a lot of us admired immensely, and still do.

ZIERLER: You connected with him on that level?

BRENNEN: I did. He wasn't easy to know, necessarily, but I connected with him, and I think we formed a connection through the years that was very important to both of us.

ZIERLER: I think it's a perfect narrative stopping point. We'll pick up next time when you start at Caltech, but maybe just a few final questions to serve as a foundation for our next conversation. Ultimately, of course, this all leads to you being a Caltech professor. Do you think it was the duality of your theory-heavy graduate experience and the experimental environment of NPL that really made you a well-rounded scientist-engineer that made that achievement possible?

BRENNEN: I think that's a very accurate description.

ZIERLER: How did your experiences complement each other? How did being a theorist at Oxford make you a better experimentalist at NPL?

BRENNEN: I don't think they did. I think those are kind of parallel but distinguishable gifts. The experimentalist came from all the things I enjoyed doing as a kid—the electric trains, and the gliders I built, and other practical things, tinkering with cars and so on. I think that was in me before I got to Oxford or to NPL or to anywhere.

ZIERLER: Was your sense when Ted made this offer—this is just a sign of how low the administrative barriers were in those days—was it really just him making this decision to offer you the opportunity, and that's all it took?

BRENNEN: Yep. It is. It was. I often wonder exactly what happened. As at other times I wondered what happened within the bureaucracy of Caltech. We'll probably discuss that later, next time. But yeah, I think that's right. I thought it was remarkable. Because I had experienced the British bureaucracy in getting my research fellowship at the National Physical Laboratory, I was a bit astonished that he was able just to make me this offer, almost on the spur of the moment. But when I got that letter, it was one of the days I'll never forget in my life. I could see myself having a real future. Being at NPL was exciting from a fundamental scientific point of view—but it was also very discouraging, because you could see people really weren't that interested in the basic science. They were interested in earning their salary and going home. They were pretty much just bureaucrats. That atmosphere pervaded the place.

ZIERLER: In him making the offer, how well-defined in your mind was your research agenda going to be to come to Caltech? Did you know what it was that you would work on?

BRENNEN: No, not really. Of course it transpired I worked on a whole bunch of things with Ted, because he was an exciting man, and very much someone that I appreciated, admired, and learnt from. He remains one of the great heroes of my life. There was one other professor who was a special mentor to me, and we'll talk about him later because he really doesn't enter the picture until I got to Caltech, and that's Allan Acosta. Allan Acosta was my other great mentor, and he will enter the story in a little bit.

ZIERLER: Last question for today. In the way that you narrated your mother's dramatic reaction to you going to California, do you think there was some deeper truth there, where she recognized in you that you saw this as an opportunity to make a life for yourself in the United States? In other words, the offer to come to Caltech before you were even a tenure-track professor, did you see this as your opportunity to do that, to make a life in the United States?

BRENNEN: I did. I didn't know how it would evolve—of course I didn't know—but yes. I think she understood that, too. She certainly understood that Northern Ireland wasn't where my future lay. I think in the back of her mind she also realized that England was not where I needed to be.

ZIERLER: Next time, we'll pick up in 1969 when you come to Caltech. We'll take the story from there.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Friday, October 13th, 2023. It is wonderful to be back with Professor Christopher Brennen. Chris, as always, great to be with you. Thanks so much for joining.

BRENNEN: Thank you, David.

ZIERLER: Today we're going to start where we left off last time, 1969, when you arrive at Caltech. Just as an intellectual backdrop, in what way did Caltech's science and engineering loom in your mind before you arrived on campus? In other words, did you know about Caltech beyond Ted Wu, or was Ted really the clearinghouse for what you understood Caltech to represent?

BRENNEN: A number of points to make here. First of all, I had read quite a few papers by Ted Wu, by Allan Acosta, by Milton Plesset. Most of them concerned cavitation, so I had learnt of their work. Also, I had learnt in general about Caltech from some of the people that I worked with at the National Physical Laboratory in London who had visited Caltech and who knew Ted Wu, who knew Allan Acosta, and had great praise for the place. Also the director of the Ship Division of the National Physical Laboratory, a man called Alex Silverleaf, had spent six months at Caltech, so he was full of praise and full of information about the place. Also—and these are all bits of pieces that put together my view before we came—at this marvelous high school that I attended in my home village of Magherafelt in Northern Ireland—and I'll get you to pronounce that village name at some point in the future—

ZIERLER: Absolutely!

BRENNEN: —his name was William Todd, and he had a brother, Jack Todd, who was a professor at Caltech, a professor of numerical analysis. He was a member of the Math faculty at Caltech. So, there were lots of points of contact from which I had gained information on Caltech.

ZIERLER: We've already talked in detail about Ted. Let's start now with Allan Acosta and Milton Plesset, before you even get to Caltech. What was it that was so significant about Allan's work that you were aware of it all the way in the U.K.?

BRENNEN: Background information on cavitation. I had read quite widely on the subject of cavitation. I can't remember anything specific about Allan's works that I utilized for my thesis or prior to coming to Caltech. It was after I got to Caltech that I got to know him so well.

ZIERLER: Is this also true for Milton?

BRENNEN: Milton was a more senior figure in my mind. He was obviously someone that Ted Wu paid great homage to, who had helped Ted Wu in his career at Caltech, particularly on some of the more difficult political issues, for example.

ZIERLER: Now let's set the stage, 1969. Chris, what were your first impressions when you arrived on campus? What sticks out in your memory?

BRENNEN: Remember I had flown halfway around the world with my young wife and two young children. In fact, we had scraped up all our financial resources in order to pay for the airfares and so on for the family. So, we were extremely grateful that two graduate students met us off the plane at LAX, took us up to Pasadena, where a particular one of Ted's staff, a lovely woman called Cecelia Lin, together with Ted, had rented an apartment for us in Pasadena. We were extremely grateful that that was available to us right away. In fact, Cecilia I think stocked the fridge for us. So, there was tremendous gratitude for their generosity in providing such a marvelous welcome for us in Pasadena. From a personal standpoint, that was very reassuring. I often recall that kindness.

ZIERLER: Administratively, you joined Ted's research group? That's where you fit in?

BRENNEN: That's correct. Ted, somewhat overseen by Milton Plesset, because Milton acted, as I said, as kind of a father figure to Ted himself. Milton was quite a senior faculty member who had some sway with other faculty members, let's just say.

ZIERLER: What was Ted working on at that point?

BRENNEN: Ted was still working on cavitation. He was also working on analyses of tsunami waves, the waves that are generated by undersea earthquakes. He had already started to think about some other topics. He was beginning to branch out considerably. I can't remember whether it was just before I came, or just after I came, that he became involved in studying microorganism locomotion, fish swimming. Those were all areas that I thought were exciting and interesting to follow along with. I think in Ted's group, the first work that I did other than cavitation was on numerical calculations of large-scale tsunami waves and how they broke when they came into shore, how the waves broke. That was quite exciting. I developed a new approach to the numerical solution of those waves using the Lagrangian equations of motion rather than the Eulerian equations of motion. That was the first presentation I made at a conference in the United States, up at Berkeley.

ZIERLER: As you were explaining last time, you came to Caltech without any real clearly-defined research agenda. You were just coming tabula rasa. You were ready to work on whatever it was that seemed important and relevant at the time.

BRENNEN: Yes, I'd say that's accurate, and I was going to be guided by what Ted felt would be valuable and important research areas. Mostly I came because Ted was obviously a very inventive scientist and someone that would be interesting, and pleasant, to work with.

ZIERLER: What struck you about the research culture at Caltech? In what ways was it unique relative to what you had experienced previously?

BRENNEN: Just so smart. So, so high—high-powered and smart. Most of the people that I worked with at the National Physical Laboratory, were a little dull, quite honestly. They didn't have that excitement for new things and rushing off to try and solve an equation or do the experiment or whatever. It was that excitement that really attracted me and made me so glad to be at Caltech.

ZIERLER: How big was Ted's research group? How diverse was the area of work that it was involved in?

BRENNEN: He had a group of graduate students. Two of them, as I said, met me at LAX when I arrived, Mike Wilson and Art Whitney. Ted had about six graduate students at the time. Shortly after I arrived, Ted also took on a postdoc by the name of Howard Winet, a biologist, who was the one that really fitted into our efforts to understand biological propulsion.

ZIERLER: Did you have any interactions with Caltech undergraduates—just to foreshadow to your later interest—as a postdoc?

BRENNEN: Very little initially, really. I had lots of interactions with the graduate students, but not with the undergraduates.

ZIERLER: I wonder if you can narrate just how quickly it took for you to feel at home in California, even in the United States, and contrast that with, as you narrated to me earlier, your feelings of alienation to some degree at Oxford.

BRENNEN: Yes, yes. I don't want to overstate those feelings of alienation at Oxford because I made some marvelous friends who remained friends the rest of my life. But their society is structured a little differently. Society and the people I met in California seemed much more like the people I had known in Ireland, growing up there. There was such a huge Irish immigration to the United States, such a diaspora, that it's inevitable that there would be a strain of the Irish temperament, if you like, within the American soul.

ZIERLER: What about, uniquely at Caltech, the emphasis on just pursuing the science, and it's about what you know and what you're capable of, and not who you know and where you're from? I wonder if you could speak to that.

BRENNEN: Clearly that was a factor. It didn't really matter where you came from. Ted had a couple of Chinese graduate students who were just the same as all the rest of us, in attempting to resolve some of the issues that he was interested in addressing. I loved that sense that it didn't really matter who you were or what your accent was. You still could play a role and be respected for that role.

ZIERLER: The tsunami research, was that more of a one-off or did you remain engaged in that area?

BRENNEN: I didn't, really. In my early years at Caltech, I went off in quite a number of directions, independent, really, of Ted. Ted allowed me to do that. I wrote papers on blood flow, and in that I was helped by Harold Wayland, who was a professor in Engineering. I also did some work on isostatic recovery. I remember people like Tommy Ahrens and Lee Silver in Geology whom I interacted with in trying to solve that problem. The problem there was to try to understand the viscosity, if you like, of the mantle of the Earth, based on data on the isostatic recovery. That is to say, when the ice sheets melted, they were floating on the surface of the Earth, and the Earth would come up at a certain rate that would tell you, if you knew how to interpret it, what the viscosity of the Earth's mantle was. I'm not quite sure how I started that. I just became intrigued by the subject of tectonic plates and how the tectonic plates moved around the Earth. That was something I did at home at night.

ZIERLER: Did you spend time at the Seismo Lab before it moved to campus?

BRENNEN: No, not really, because it wasn't the Seismo people I was necessarily interacting with. I remember it was really people in Geology. I went over and gave a seminar in Geology at some point in the first year or two that I was at Caltech.

ZIERLER: What were some of the early signs as a postdoc that this would transition for you into a tenure-track appointment? Who were you talking to? How did you feel yourself about what your prospects were?

BRENNEN: Let me factor Allan Acosta into the picture, before we get too far. Ted had housed some of his graduate students in the Kármán lab—he was based in Thomas, but like a group of his students, he found an office for me in the Kármán lab. The office I had in the Kármán lab was one of a pair of offices which had a secretarial desk in between, but there was no secretary there. The other office was occupied by Allan Acosta. He and I hit it off immediately, both personally and eventually in terms of the research interests I had. Allan Acosta was a frequent companion of mine in various discussions of various problems. He entered the picture very early. Maybe I'm going a little bit ahead of myself, but we started to talk about the cavitation work that I had done, the numerical solution to various cavitating flows. He told me about his work on cavitating pumps. I became at that point quite interested in how I could use the tools I had, the computer solutions, to solve the flows in pumps. The objective was to predict the performance of a pump which was cavitating, which wasn't something you could do readily.

At some point—and the schedule isn't too clear on me—Allan said to me, "I've had a contact from this fellow in NASA, in Huntsville, Alabama, who wants me"—wants Allan, that is—"to see what could be done to predict not just the steady-state performance of these cavitating pumps in a rocket engine but how that cavitation would respond to oscillations." We'll come to that description of why he wanted to know that in a little bit. It was clear to me from the discussions that I had with Allan that there was a serious problem in rocket engines, right from the beginning, and I'll describe that serious problem. That was a really critical problem. I'll call it the pogo instability. Let me just take a moment to describe that, because that's central to some of the descriptions I'll come to. The pogo instability is something that works as follows. If a rocket takes off and begins to oscillate in a longitudinal structural mode, that causes pressure and flow rate oscillations in the fuel tanks and in the oxidizer tanks and therefore at the inflow to the engines. Engines of a rocket engine are basically two enormously powerful pumps that pump the oxidizer and the fuel to the combustion chamber. If the flow into them is oscillating, the produce a fluctuating thrust of the rocket. This may then amplify the longitudinal structural oscillations of the rocket. That's it. It's like a pogo stick, if you like, the kid's toy of the same name.

No one seemed to really have a handle on how this all worked, how this instability developed. It was key, obviously, to understand how the cavitation responded to these oscillations, because that would determine the relationship between the flow into and out of the pumps. To be able to predict that, you had to be able to know and predict how the cavitation in the pump responded to these oscillations, at a whole range of frequencies. I hope I'm not putting too much detail in.

ZIERLER: Not at all.

BRENNEN: Many of the early rockets, not just NASA but also the French and Russian rockets, had self-destructed because of this instability. In other words, they'd fly up to a certain point, they'd start to oscillate so badly the rocket would come apart. That was a real serious problem. The thought that they were going to send men up in these rockets and have to experience this was another even more appalling consequence. Folks at NASA Huntsville had contacted Allan because they knew of his work on pump cavitation, and had asked Allan to go back there—and I'm talking about somewhere in the very early 1970s—to go back to Huntsville, Alabama, to talk to them and to see what we might do to try to solve this problem. Allan said, "Well, why don't you come along, Chris, and maybe we'll be able to figure out some approach together?" So, I went with him.

I remember going on my first visit to NASA Huntsville, to this already somewhat legendary place, because lots of the German rocket scientists, remember, were almost kidnapped and placed there after the Second World War, and there was still an aura of Wernher von Braun and the Peenemunde kids, as they called them, the younger people who went with von Braun to Huntsville, Alabama. We went there and had long discussions, and that led to a significant research contract which then went on for years later. The objective was to come up with a model of the dynamics that led to this instability and to try to solve that problem.

Allan and I also got along very well on a personal level. Allan was interested in sailing, and so he said, "Why don't you come sailing?" It wasn't long before I was off in Allan's sailboat in various races across to Catalina Island and so on. He had some of the personal characteristics of my father, so I saw Allan as a close father figure, I think, in the early days. He was very good to me and helped me promote my case at Caltech, and so on.

ZIERLER: That's to say that you were making the case yourself? You were saying, "I'm thriving here, I'm doing important research, I think I'm worthy of consideration for a tenure-track appointment"?

BRENNEN: Yeah. I mean, it didn't happen very fast. It took a while, I can't tell you how long—six or seven years. In those days, Caltech had a career ladder, if you will, that went from research fellow to senior research fellow to research associate to senior research associate. I made my way up that ladder. When I look back, it was very valuable, because I was able to focus almost exclusively on my research during those early years, those five or six years. To build a reputation, publish papers, make conference presentations and so on, during that period. That was very valuable.

ZIERLER: What was your funding source during those six or seven years?

BRENNEN: Ted had funding from the Navy, the Office of Naval Research. We also had a contract with the National Science Foundation. Then there was the support money we got from NASA. Those were the sources of our funds for research.

ZIERLER: Caltech of course was in the early 1970s, the late 1960s, was much less political than other American campuses. Did you detect any politics, any talk about the Vietnam War and civil rights, and things like that? Did people talk along those lines?

BRENNEN: Yeah, they did, obviously, but not with the same kind of intensity, perhaps, as you'd find at other places which had humanities programs and so on. No, no. In particular the engineers tend to be somewhat apolitical. I think I was perhaps more political than most.

ZIERLER: Tell me about finally joining the faculty. Where did the offer come from? How did you feel at that point?

BRENNEN: There was a significant amount of give and take before I got to that point. I was encouraged at one point to go and apply to other universities, and I got several offers from other universities, which I turned down because I thought there was still a chance at Caltech. It was a moment of great joy when I got the offer of tenure as an associate professor. I was never an assistant professor, you see, because of those years I spent as a senior research fellow and so on. I was never an assistant professor. I went straight to being an associate professor and then I got tenure. Tenure was the key thing.

ZIERLER: Nowadays, as you might know, Caltech has done away with the associate designation. In those days, when you achieved associate, that meant you got tenure?

BRENNEN: No, not necessarily. I became an associate professor first, and then, a year or two later, I was given tenure.

ZIERLER: I see. The associate was in recognition of your seniority and then obviously the tenure clock was sped up for you, to some degree?

BRENNEN: That's right.

ZIERLER: Was there a tenure talk? Was there an opportunity for you to reflect or assess on your research achievements and to convey that to your colleagues?

BRENNEN: There were a number of talks, but I remember one in particular that I knew, because of what Allan and Ted said, was going to be important, and most of the people with any connection with my research, most of the faculty, were going to be at this talk. I remember that talk very well. It was frightening, to know that your future was dependent on what this large group of professors in the seminar room were going to think about what you were doing.

ZIERLER: At that time, either before you got tenure or right after, what was your research agenda? What contribution did you see yourself making in the long term to the faculty in EAS?

BRENNEN: The subject of unsteady cavitation and the use of cavitation in a multitude of different technologies was clearly important, had become increasingly important, not just to NASA but to a wide range of industries, and in medicine. The uses of cavitation, and of course the damage done by cavitation, both of those were big issues. There were industries where cavitation caused a lot of damage. There were other industries that were making use of cavitation for a whole variety of different processes. Medicine was perhaps the one that seemed most exciting to me, though I didn't get into that until a little later, at least until after I had my tenure.

ZIERLER: Is that to say, given the relevance of unsteady cavitation to technologies and industry, did you gain a greater interface with the world of business than many of your colleagues might have?

BRENNEN: I think that's probably true, yeah. I did a lot of consulting for various companies—aerospace companies, hydraulic machinery companies, and with some biomedical applications. Just to quote one example, I spent a good bit of time on a project which was designed to deliver very super-saturated solutions of oxygen into the heart or into the brain in order to prevent the damage in the aftermath of a stroke or a heart attack. What happens in the heart or the brain is the damage is mostly done by oxygen starvation, and if you can get oxygen in there in any form, you can aid recovery—but you can't create bubbles. If you created bubbles, then that would kill the patient. There was a very interesting project that a small company down in Orange County embarked upon to try to promote that therapy. In the end, they never really got NIH approval—because it seemed such a dangerous thing to do, to inject highly super-saturated fluid into the brain or into the heart. But it was a marvelously interesting program to get involved in.

ZIERLER: What's the mode of connection? Are you doing research and you recognize that something is industry relevant? Are you something of a known quantity at this point and people in industry are coming to work with you? How does that work?

BRENNEN: I'd say the latter, really. These were primarily consulting projects for which I got paid, and that was certainly not an inconsequential result. Many of the consulting projects I did had to do with pumps, with very mundane pumps, or with propellers, devices that are very practical.

ZIERLER: Are there scientists in industry that they hit a wall and that's where they come to you—you have a level of expertise, you're working on this—where you have solutions that they can't achieve on their own?

BRENNEN: Sometimes. Certainly with respect to the NASA problems and solving those problems. In particular, the business about the unsteady response of rocket engine pumps, I was doing most of that work before the space shuttle design was complete, so it was critical, in order to prevent the onset of that instability in the space shuttle, that that be solved at that point. In fact, we managed to do that, because the space shuttle never really experienced that instability which caused the destruction of so many earlier rockets.

ZIERLER: Tell me about building up your own research group. Perhaps we can start with what model Ted might have provided you as an ideal for creating a dynamic group that could attract excellent students and really do field-leading research.

BRENNEN: Both Ted and Allan Acosta, more particularly Allan Acosta, but also through Allan I became quite close to Rolf Sabersky, with whom I did a number of projects, which we'll come to a little later. All of them, they would suggest to me, in graduate student applications, applicants that I would look at to consider taking on, on my own. That's how I acquired most of my early graduate students. I think when you're a younger faculty member you don't get the very best. It took a while for me to get the best of those graduate students. I learnt to be able to acquire some of the best graduate students as time went on, let's just say that.

ZIERLER: What were the kinds of interests that graduate students would be attracted to, to join your group?

BRENNEN: All of the subjects that I was involved in. There were problems of unsteady cavitation. There were problems that I dealt with in water waves. There were problems I dealt with in other areas of research in which I was involved. The flow of granular materials attracted a lot of people, because that was fun. That was a fun subject, and a novel subject. That was to uncover the dynamics and the acoustics of flowing granular material like sand. No one had really tried to analyze or understand that before. I remember one of the first expeditions I made in that regard. I had heard about these booming dunes in the Mojave Desert and elsewhere. I had heard about booming dunes, these high sand dunes, in many places around the world, that at some point would give off this booming sound—boo-ooh-ooh—and no one really understood why or how. The booming was a subject of great legends among many of the people native to those parts of the world.

We knew the dunes out in Mojave, and so one of my graduate students and I set out one day to drive there. At that time I had already acquired an off-road vehicle that I had used to go on my personal explorations around the state. We set off in this off-road vehicle for the Mojave dunes, which are miles beyond Barstow. We climbed up these dunes and, at the top, realized that if you sat down on the leeward side of the dune, that you could make it boom just by skirting down on your rear end. So, there we are, up at the top of this quite high dune, making the sand flow down the leeward side, and the whole dune would go, "Boom-boom-boom." It was a weird sound to experience. No one had any understanding of why they made that noise.

That set off a series of research projects to measure this sound, to understand the circumstances in which it occurred, and to try to understand the source of the sound, which we did. We did get to a point where we understood what made that sound. That was fun . I enjoy the outdoors, as you know. I enjoyed the opportunity to take graduate students out to the Mojave Desert in the blazing heat, climb up these dunes, and then get down on our rear ends to make the thing boom! We measured the booming sound, when it happened and how much it boomed. We stuck instruments into the dune to see where it was making sound, where the sound came from, and so on. We used ground-penetrating radar to see how deep the movement penetrated. Booming dunes was a fun project.

I had another student who made a computer model of flowing sand. That was interesting from a completely different point of view, in that you had to devise a way of solving these flows. These weren't like water or air or anything; these were particles that banged into another, so you had to figure out how to calculate those flows. We did so by devising a new computational approach that utilized a potential collision list, in which you calculated all of the possible collisions that might occur. Then you solved for the first collision, figured out the new trajectories of those particles. Then, you calculate a new set of possible collisions which you add to the list. You keep on solving this problem, solving all the collisions between particles, and thus understand the flow that would occur. Later on, I had another student who studied the sound experimentally, by placing a large acoustic speaker on a bin of sand, and examining what came out the other side.

ZIERLER: Was any of that work industry-relevant, the dune work, or that was all basic science?

BRENNEN: It was mostly basic science, but there was real interest in many of the industrial processes which use granular materials—large grain elevators, for example. Some of the explosions that occur in these grain elevators could destroy the elevator itself. So, there was a real interest in that subject from that point of view.

ZIERLER: We've already talked earlier in your career about how you utilized your computers. What about in your early faculty career at Caltech? In what ways were some advances in computers or computational science relevant for you?

BRENNEN: As in the example I just gave you of granular material, we devised our own computational approaches. We just used whatever computers were available. I remember transitioning to various programming techniques and utilizing decks of cards, and huge decks of cards at one point, when we had an IBM computer at Caltech that required cards to be fed into it. We just evolved with the availability of those computers. We didn't really design computers in any sense.

ZIERLER: What did you find was the ideal number of graduate students and postdocs to have at any one time? The size of your group, did it fluctuate over the years? Did you want it to always remain steady?

BRENNEN: Yes, tried to keep it steady, because you have a responsibility to support the students. I always felt the best number was five graduate students. Some of my colleagues went significantly larger than that, and of course in areas like chemistry they have huge groups. I always felt that that was not doing a good service to those students, because part of the value of being a graduate student is interacting directly with the faculty member. I didn't want to go beyond the point at which that communication was limited.

ZIERLER: As a junior faculty member, even after you achieved tenure, did Ted remain something of a mentor to you, or does by definition the relationship change when you're both tenured professors?

BRENNEN: I'd say it changes. My interactions with Ted gradually faded away, not completely but they faded away. Allan was then more of a mentor to me. Then there were other faculty members who certainly helped me at the time, people like Tom Caughey for example, and Rolf Sabersky, and other people in the Engineering building. Also of course I came to have interactions with faculty from all over Caltech. That was one of the great values of the small size of a place like Caltech. I sat down the other night to think about all the faculty members that I interacted with or wrote paper with, or even just gave me advice on a topic of interest to me. Every one of the divisions, with the possible exception of Humanities—I can't think of who I may have interacted with there, except as friends—but in Geology; Biology; in Physics, Math, and Astronomy; and in Chemistry, I had interactions with all of them, and wrote papers with a lot of faculty from all over Caltech.

ZIERLER: What was it about your research that made it so amenable for what we now call interdisciplinary research, the fact that you could have collaborations with essentially professors all across the Institute? What was the transportability or the relevance of your work in all of these different areas and applications?

BRENNEN: Most of the good science is done at the interface between disciplines. You find yourself at one of those interfaces quite easily, I would say, whether it be with biology or geology or chemistry. Of course I made an enormous number of friends at Caltech during my time there. Especially as time went on, when I became involved in student affairs, I made friends in all of the divisions, including the humanities. Those friendships led to interactions, too. Some of them were very exciting and interesting to be with. I became very friendly, of course, as maybe you know already—for example in Math, I became very friendly with people like Gary Lorden and David Wales; in Chemistry with Bob Grubbs and Harry Gray; and in Physics—I think maybe I described to you already how I first got to know Dick Feynman, in an unusual way. Did I describe that to you before?

ZIERLER: No, please! I never tire of Feynman stories! Please tell me how you met him.

BRENNEN: That's great story. Here I am, fairly recently arrived from England as a young faculty member, and somehow I got to know Shirley Marneus, who was at the time the person who produced and directed the theatrical performances by Caltech students. At that time, they would put on a musical every year. Caltech students are not, in general, natural in the theater. The year after I arrived, they intended to put on this production, Shirley did, of Guys and Dolls, the Hollywood musical with which you're probably familiar. They needed an Irish policeman, and they somehow learnt that I had been involved in various theatrical productions in my homeland, so they asked me to play the part of Lieutenant Brannigan in Guys and Dolls.

ZIERLER: [laughs]

BRENNEN: There were four faculty that had notable speaking parts in that production. It was a remarkable group. I don't count myself at remarkable, at that time, but one of them was Richard Feynman, who was going to play the bongo drums in this nightclub scene and various other small speaking parts. He was to use his Brooklyn accent at one point, for some purpose that I now have forgotten. One of the other faculty involved was Jenijoy La Belle, who at the time was going through various difficulties at Caltech which I don't need to go into. The other was Harry Gray. Harry was Harry the Horse, one of the gamblers in Guys and Dolls. These were all small parts, and like all theatrical productions, you spend a great deal of time during rehearsals sitting around backstage, waiting to go on. It's not a very efficient process. So, I sat around backstage with Jenijoy and Harry and Dick Feynman, and I got to know them. It was truly a marvelous experience, because I got to see how Feynman's mind worked—he had never been in a theatrical production before, so he would ask me, "Chris, why do you do this? Why do you do that? Why do you do this?" Of course most of the things I couldn't answer, because I hadn't really thought about why you did it; it was just something that came naturally to an Irishman! That's how I got to know Dick Feynman, and Harry and Jenijoy. They remained friends throughout my time at Caltech.

Later on, of course, when I became dean of students, I asked Dick Feynman on quite a number of occasions to give talks to students and he loved to do that. He was excited to interact with students. He was like a great Irish storyteller. He loved to tell stories. He just absolutely loved it. He would sit on the wall at Freshman Camp telling students all about the decipherment of the Mayan hieroglyphics or a multitude of different subjects.

It was not long after Guys and Dolls that that Jenijoy went through her problems with tenure. I greatly sympathized with her and so did Feynman. Even though it's not often said, I know that Feynman was helpful in resolving that situation with Jenijoy.

ZIERLER: Oh, interesting. I did not know that.

BRENNEN: Yeah, and they got to know one another, I think in part, through Guys and Dolls.

ZIERLER: Interesting.

BRENNEN: I don't know the details, except that Jenijoy and I remained friends. I haven't seen her in a long time, but we remained friends for many years after that.

ZIERLER: Unavoidably, because gender played a role in this issue, some general questions. You came the year before women joined the Caltech undergraduate student body. 1970, of course, was the first year that Caltech went coed. You were a postdoc at that point. You didn't have much interaction with undergraduates. But did that register with you at the time, that Caltech was looking to be a more what we now call diverse place?

BRENNEN: I thought that was a necessary step for the Institute to take. It certainly registered with me.

ZIERLER: What about women faculty members? Were there any women faculty members in EAS when you joined the faculty?

BRENNEN: No, there were not, and I felt that was a singular deficiency, in Engineering. I don't even know that there were many in the Institute as a whole. Olga Todd, interestingly enough, married the Jack Todd that I told you about earlier, but I didn't really know her at all. I'm trying to think of who was the first that might have been hired after that but Melany Hunt came shortly after.

ZIERLER: Last time we talked about the duality of your more theoretical graduate work and your more experimental first postgraduate appointment. How did you weigh experiment and theory as a faculty member at Caltech? Was it a balance? Would you have focused more on one or the other, or was it really dependent on whatever given project you were working on?

BRENNEN: I'd say the latter is a better description. I loved doing experiments. I always had. Even though I may not have started out as an experimentalist, I felt I had. Because of my interests as a young kid and my involvement with various machines and so on—my father's lawnmower and so on—I felt I had a real interest in devices, in things, in experiments, so I was very interested in that. Some of the experimental facilities that I built, I still feel very proud of, when I look back.

ZIERLER: What are some of the experimental facilities that you built?

BRENNEN: Perhaps the most famous one is a facility to measure the dynamic response of a cavitating pump. This came from the NASA contract. NASA wanted us to try to reproduce the dynamics of an oscillating flow into a pump on a small scale. Obviously it had to be done on a small scale; couldn't do it in a full rocket engine. And, you couldn't do it with liquid oxygen or liquid hydrogen; you had to do it with water. So, there were some real scaling issues and problems. I, along with Allan Acosta, built a facility to measure the dynamic transfer function of a cavitating pump. In other words, we built a facility in which there was a pump that was cavitating. We were able to observe the cavitation and then we fluctuated the flow going in and out, at a whole range of frequencies, and examined how the pump responded to those frequencies. We constructed what's called a transfer function, a dynamic transfer function, for that pump, using these experimental methods. Then we compared it with the various theories that I had as to how it would behave. That experiment won a number of prizes with ASME and was, I think very much a part of solving that rocket engine problem, because they could take my experimental results, perhaps more reliably than the theory, because the theory had some big holes in it that you couldn't really nail down, and required the experiments in order to nail it down.

That was perhaps the most sophisticated and important experiment that I did, but there were other experiments. I haven't told you about the experiments I did in the Vomit Comet [laughs]. That was another adventure, to say the least. This had to do with studies with Melany Hunt, studies of the fluid mechanics of particles in liquids. You could do a lot of experiments, of course, on the tabletop bench in the lab, but there were certain experiments you couldn't do because of gravity, because the particles would settle out and so on. At some point, we convinced NASA, the people who ran the Vomit Comet, which is an airplane, an experimental research airplane that NASA, I think, still uses. The plane does up and down, like this. Let me see if I can get it on the camera here. It goes up and down, and when it's going over the top, you get 25 seconds of zero-g, and then 25 seconds of zero-g as it's going under the bottom. The plane would fly along at some altitude, flying this sinusoidal trajectory. During one flight, you'd get 40 periods of 25 seconds during which you could have zero-g. We designed this experiment to measure what these fluid particles would do under these conditions. I actually flew seven flights on the Vomit Comet. That's seven flights of 40 parabolas—their name for going over the top "parabolas"—so, if you like, 280 periods of zero-g. For one set of flights, we went down to Houston. For another set of flights, we went up to Ohio, to fly on this plane. I have video of me floating in space in between these experiments and projecting myself flying up and down the cabin.

ZIERLER: Oh, if you're able to share it, I would love to see it!

BRENNEN: Sure, I can give you the pieces of video for that.

ZIERLER: What's it like? What's the sensation like when you're up there?

BRENNEN: First, there's always a doctor on the flights, so they give you some medication so you don't vomit over the whole plane of course, over the experiment. That's the first thing to mention. But nevertheless, the first one or two of these parabolas, your stomach is coming up and down. You have to learn to suppress things. But after a while it doesn't matter. The most interesting part is how you handle yourself. It's amazing, it's not quite like swimming underwater, which I've done a lot of also, because there's no resistance to your tumbling motion in an airplane like that. See, underwater, there's a lot of resistance to your rotation, to your tumbling. In space, there's not that resistance to tumbling, so you have to be very careful the way you push yourself off from the side of the interior of the plane, otherwise you end up tumbling out of control. That was the first thing to learn, how not to tumble. But it was a lot of fun. I have to confess, despite all that effort, 280 parabolas, the experiments never worked. We could never get the thing to settle down within 25 seconds in order to take decent measurements.

ZIERLER: What was the actual research question? What were you looking to find?

BRENNEN: The question was to figure out what the effect of viscosity, what the effect of rheology is, in a mixture of liquids and solids. That was the objective. This was done in collaboration with Melany Hunt, who was another of my collaborators down through the years. She was very interested in that but not very interested in going up in this airplane and being tossed around in the middle of the air, so I, in some sense, substituted for her on those experiments.

ZIERLER: What was so difficult? Why couldn't you get it to work?

BRENNEN: We couldn't get it to settle down in time. You would start with this mixture, it was supposed to kind of mix out and come to a steady state before the end of this zero-g period, and it just did not. We tried a number of things to try to get it into a steady state, but it never got into a steady state, and so the results were not very useful.

ZIERLER: You mentioned all of the collaborations across campus. What sticks out in your memory that was most scientifically significant?

BRENNEN: I don't think I can answer that, David. That's one of those questions where others judge what's significant and what's not. Only time will tell, in many instances. To this day I'm surprised by what papers of mine—and I wrote, after all, over 300 papers, and I sole-authored four books, and a bunch of other stuff—I'm still surprised at what gets referenced and what doesn't. Some of the things that didn't seem to me to be terribly significant seem to get referenced all the time. Other things that I thought were very exciting and novel don't seem to get any reference. It's a puzzle, that. I think, of my books, the cavitation book seems to get the most references. I think it's a good book. I think it still has relevance even 30 years later.

ZIERLER: I'll reframe the question. If not on significance, what was most personally meaningful to you? What was the collaboration where either you learned the most and improved your skills as a scientist, or perhaps simply you had the most fun doing it?

BRENNEN: I had a lot of fun with the facility that I built to measure pump transfer functions. It it was a very challenging experiment. We had to design new equipment and devise instrumentation to make the measurements. For example, how do you measure unsteady flowrates into and out of a pump at frequencies up to 30, 40 hertz? No one knew how to do that. It wasn't until I realized that I could adapt an electromagnetic flowmeter to do that, that we accomplished the measurement. That was essential in getting the experiment to work. In addition there were other instrumentation efforts. Eventually that facility was copied by quite a number of investigators around the world—in Japan, in Italy, in France. In the end, when we were done using it, NASA came and dismantled it and took it all back to Huntsville, Alabama, where they were intending to reconstruct it. It was a unique facility. Others did try to copy it but didn't really understand exactly what they were doing in my opinion. They didn't get the value out of it that we got out of the one we built in the basement of the Thomas Building. That facility I look back on as a real achievement.

ZIERLER: Was JPL an asset for any of this? Did you work up on Lab? Did you have collaborators there?

BRENNEN: I did, but not in this area. By the time we started that project, JPL wasn't doing any work on conventional rocket propulsion. But I did have significant interactions with JPL on the sand business, because one of the real issues for the rovers was their ability to maneuver on the surface of the Moon or on Mars. I remember getting involved in various problems. When one of the rovers got stuck in the sand, heading for a crater, they called me and a bunch of others in to try to figure out what the best way to get this rover out of the sand dune. That was a fairly easy question to answer; you just put your foot on the gas and back out like crazy! [laughs] That's what they ended up doing. I have a picture—there's a movie on that subject. What's the movie called? It's quite a good movie, actually. Goodnight Oppy. There's a shot of me actually sitting up at JPL in this meeting, trying to figure out how to get it out of the sand dune.

ZIERLER: The last topic I want to cover today which will serve as a basis for our next discussion is the prelude to you becoming dean of students. Before you were named to that position, did you already display an interest in the undergraduate student body? Were you close with undergraduates? What might have explained how you ultimately were named to this?

BRENNEN: The first position in Student Affairs that I officially had was not dean of students. It was master of student houses. The question is still relevant. Allan Acosta had been going to Frosh Camp, which at that time was the freshman orientation that took place on Catalina Island. He would sail his boat out each fall in order to participate in freshman orientation. Because I sailed with him, he asked me on a number of occasions to go out there with him to help sail his boat over to Catalina and to attend the frosh orientation. Which I did, and so I got to know something of the undergraduate business. I got to know David Wales, for example, during one of those early frosh orientation sessions, because he was the associate dean of students. That's how I first learnt many of the issues and programs in student affairs.

ZIERLER: What were some of those issues?

BRENNEN: You mentioned earlier the Vietnam War; the racial issues; the problems at Caltech of attracting minority students, so as to provide an appropriately mixed student body at Caltech. All these issues were important and required thought and conversation. But I had fun, too. I enjoyed Frosh Camp. I enjoyed sailing over there, enjoyed meeting all the students. I guess they got to know me somewhat. It wasn't too much later that Sunney Chan, who had been the master prior to me, decided he had had enough. The students and the faculty committee involved with student affairs were to look for a new master of student houses. Doreen, my first wife, and I gave that considerable thought and discussion. I realized it would impact the time I had available for my family, the time I had available for the science, but I nevertheless felt it would be something that I would really like to do.

ZIERLER: Meaning you recognized it was a significant commitment of time.

BRENNEN: Yes, absolutely. Not just time, but energy, especially dealing with students with serious problems.

ZIERLER: The idea is that when students have those problems, you're the first person they go to?

BRENNEN: That was not exactly true, because the first line of defense was always the graduate students or postdocs who were the resident associates in the undergraduate student houses. I supervised and guided them and got to know them all very well. They would most often be the line of communication to me to let me know of difficult problems. I suspect we're going to deal with that in more detail later.

ZIERLER: We will. Last question for today—on that basis, Chris, when you first got involved in this work, what level of appreciation did you gain for Caltech in seeing the students in this context? What did you know institutionally about Caltech through the undergraduate perspective?

BRENNEN: That's an interesting question. I realized that it was very difficult for many of them. Many students came to Caltech—undergraduates now, we're talking about—having been highly successful at their high school and had to face the difficulty of finding their own initiative, their own determination, rather than gaining that from being better than the other students around them. I think I had some awareness of those issues from my interaction with my fellow students at Oxford and recognizing some of the difficulties that they went through as undergraduates, so there was some carryover there from my days as a student in Oxford.

ZIERLER: On that note, we'll pick up with your ongoing work with undergraduates, your research, the cavitation book—we need to get to that—and of course dean of students. So much more to cover for next time.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Tuesday, October 17th, 2023. It is great to be back once again with Professor Christopher Brennen. Chris, as always, wonderful to be with you. I look forward to continuing our conversation.

BRENNEN: Thank you, David, and it's fun to see you again.

ZIERLER: Today I want to take a brief interlude from all of your work on behalf of undergraduates at Caltech, and I'd like to ask a few general questions about a topic we touched on briefly but I think requires a little bit more explication, and that is how you got involved in consulting in the framework of national security work and classified matters. Before we get into any specifics that you might remember, I wonder if you can explain generally what kinds of areas of expertise you gained that were relevant to the national defense of the United States.

BRENNEN: I think knowledge of the phenomenon of cavitation is the simple answer to that. There are many aspects to that, but they have to do with the noise generated by cavitation, by the instabilities generated by cavitation. That's the most simple answer to your question.

ZIERLER: Without getting into specifics, obviously without divulging anything sensitive, is cavitation relevant for everything from weapons systems to stealth technology? Where might we see the application of cavitation expertise?

BRENNEN: Specifically on submarines and other high-speed vessels, and then with torpedoes, if you like, and other fast-moving underwater bodies. Then listening for the same, with our own microphones or hydrophones, at ocean depths.

ZIERLER: As an immigrant to the United States, what did it feel like to get a security clearance, which is really a symbol of your loyalty to the United States?

BRENNEN: I was proud of getting that, but most of all, I looked forward to the technical challenges that that allowed me to address. I think those are the simple answers to that.

ZIERLER: Would you go to Washington, or was all of this work done locally in California?

BRENNEN: Some of it was in Washington, yes, with the Navy there. Some of it was in a large Navy lab in Memphis, Tennessee. Some of it, of course, was also associated with NASA, and with the rocket engine turbo pumps that cavitated, as we discussed before, with some detriment to the performance of the rocket engines. Those are all pieces of that, and they stemmed from basic knowledge of cavitation, cavitation noise, cavitation dynamics, and the performance of devices like high-speed pumps and propellers.

ZIERLER: I wonder if this opportunity was a two-way street for you. In other words, your interface with the military and national security, did this push your research in new directions? Did it influence your own scholarship on cavitation?

BRENNEN: Yeah, you always pick up little strands of information through contacts like that, and you recognize what people think is important, and are therefore able to factor that into what you consider to be the most crucial parts of your research.

ZIERLER: We talked a little bit about the kinds of careers that your students went into. When you got involved in national security work, did you realize that government service, working for the U.S. government or the military, was a viable career path for some of your students?

BRENNEN: Yes, indeed, but mostly at big Navy or NASA labs. Several of my students, several graduate students that I advised and helped, went on to work particularly at the Navy labs in Washington, D.C., though a couple of them went to work for NASA also, in Huntsville, Alabama.

ZIERLER: Let's now return to all of the work that you did on behalf of undergraduates at Caltech. Tell me a little bit about the position, dean of students, and your awareness of its history. How far back does that go, the dean of students, at Caltech?

BRENNEN: Oh, it goes way back. I have a list of the—in fact I made a number of lists, out of curiosity, of people who had served in all of those positions. I can look that up for you, David. I have it in my files. I think the dean of students goes right back to the beginning of the Throop Institute of Technology, perhaps goes back to the 1900s, somewhere in the turn of the century to the 1910s.

ZIERLER: Is your sense that it's a very natural progression from master of student houses to dean of students? Is that a common trajectory at Caltech?

BRENNEN: I think so, though the master of student houses position no longer exists, regrettably I think. I think it was a mistake for the Institute to abolish that position. I understand there were reasons why, but I still think that that direct contact between someone in authority in the administration and the students in their living environment was a very valuable contact. There were a number of circumstances, which we can get into, where I was able to act in a way that an ordinary staff member would not necessarily be able to act. I felt a freedom. In fact I think at one point Murph Goldberger said to me, "You know, Chris, we want you to take care of the problems. Don't necessarily bring them to me."

ZIERLER: [laughs]

BRENNEN: Murph was the president most likely to say that kind of thing.

ZIERLER: Who asks you to become dean of students? Is it the provost?

BRENNEN: We need to go back to the master, because when I first got involved was as master. It was kind of a natural progression to become the dean of students, because by then I had learnt a lot about student affairs and about what was important and what was not important. And, I had learnt a lot about how I could serve the students, as dean. So I think it's much more important to maybe focus on, or ask, how I got involved to be master of student houses. That's got a fairly simple answer, actually. I was a young faculty member, pretty much unknown to most of the undergraduates, but I did have an advisee by the name of Barbara Turpin. Barbara is now a professor at the University of North Carolina. She was my advisee, and the president of Dabney House. Often she came to see me about academic matters, her own program. On one occasion, she asked me—because we got along quite well—"Chris, is there any chance you might be willing to become master of student houses?". I said, "Yeah, I might think about that." I knew several of the previous masters, in particular Sunney Chan, and before him Jim Meyer. So I said, "Yeah, I might be interested."

Then, at some point, I had the most extraordinary interview with the students and the faculty committee on student housing. They all gathered in the master's office. It was the one and only time when I've been interviewed by roughly 25 people all at once, students and faculty. I hadn't made any great determination at that point whether I would accept it, but they wanted to interview me for it. I think the interview went quite well. I think it was Jack Richards who called me a little bit later and said, "We'd like you to become master of student houses." Jack was the chairman of the student housing committee at that time.

ZIERLER: What was the impact of this on your family, becoming master of student houses?

BRENNEN: Good question. I tried to project it forward to see how it would affect my family. It did have a significant effect on my family, not all good, I will admit. When I look back, I have some regrets about the fact that it had some negative impacts on my family. I didn't get the time to spend with my children or my wife that I had had prior to that commitment. I look back on that with some regrets, I must admit.

ZIERLER: This is because it was such a large time and energy commitment?

BRENNEN: Energy and time, yeah, and it was very difficult to avoid that because, first of all, most of the students lived at night, and so in order to meet with them, I would go on my walk around of the seven houses. I usually set off for my walk around the student houses around 11:30 at night and got back about 1:00 or so. I did that virtually every night that I was master of student houses. I would start off by going through Page, and then down through Fleming, through Dabney, and around the back to Blacker and to Ricketts, over to Lloyd, and then to Ruddock. The presence I created in the houses at that time of night was very important in terms of keeping my finger on the pulse of student matters, giving them a chance to talk to me if they wished to talk to me, and of supporting the resident associates, because they were for me the main first step in counseling students. The students would often come to see me at those late hours, but it meant that it impacted my family. I do regret that impact on my family.

ZIERLER: Did you become a known entity in making the rounds on such a set route? Did students know that's where they could interact with Professor Brennen?

BRENNEN: I think so, absolutely. I got to know them well, individual students who were in particular able to tell me what the mood of the house was or give me the inside scoop on some of the problems that had arisen, tell me about students who were deeply troubled. Those were all things that were important to me. When I look back, I think it was a job well done, but at the sacrifice of my family's time.

ZIERLER: What was an example of an issue that you could resolve on your own, and what were issues where you needed to either kick it up the chain of command or bring in others who had different expertise than you?

BRENNEN: There were a lot of individual student problems that I dealt with on my own. Many students came to have confidence in my ability not to take the matter any higher if it wasn't threatening to other students. I often counseled students and student groups, quite extensively. Aside from those walkarounds, I would often go to dinner in each of the student houses. In particular, I had a relationship with Dabney House that had preceded my time as master of student houses. Dabney had had some real issues with the drug culture in its time, and that was an issue that I needed to deal with, but I needed to deal with it in a way that helped the problem rather than hindering it.

ZIERLER: Why would students turn to drugs, do you think? Was it high pressure? Was it peer pressure? What was it?

BRENNEN: It was their own pressure. The main problem was speed. Speed in order to complete assignments, speed in order to complete their assignments on time. It would just get worse and worse and worse. A student would get into serious problems with the speed that they took. Marijuana didn't bother me, especially. It made them sleepy. But then there were other drugs around, LSD and so on, that were very dangerous. Those other drugs were individual student problems. They weren't a big group problem.

ZIERLER: Were there ever instances where you needed to talk to parents? Was that permissible?

BRENNEN: That was very tricky. Very tricky. There were times I had to talk to parents, of course, but it had to be done very carefully to avoid making the problem worse. The issue of parents is something worth mentioning. One of the great surprises to me when I became master was not that the students were bright—we knew they were bright. As a regular faculty member, you imagine that they must have come from good homes, and been well treated as kids. The shock to me—and I don't want to overstate this problem, but the shock to me was how many of them had been abused, physically, even sexually, but certainly psychologically, by their home upbringing. That was a real shock to me! It was hard to imagine that these high-performing kids would have such problems. I have to say that most of the substantial problems arose from that upbringing, from their childhood abuse, if you like. There were certainly problems when I had to call the parents, but the first stop in dealing with many of those problems was to get them into some psychiatric care. There were quite a large number of cases where I would call the Institute psychiatrist, and he and I would come up with some way to get them to the health center or psychiatric care, or even at the worst, getting them to the Huntington. I remember several instances driving a student to the Huntington Hospital so they could be seen and committed to one of the local psychiatric clinics. That was a pretty eye-opening experience.

ZIERLER: Did your find your fellow professors to be generally knowledgeable of when students were experiencing such troubles? Would you talk to them about it?

BRENNEN: No, I didn't. The only ones I talked to were really my two student affairs comrades, Gary Lorden and David Wales, who were familiar with the problems and could advise me. I consulted with them on almost all these cases, and I consulted with them privately, of course. We would together often come up with a strategy for helping the student deal with the problems.

ZIERLER: Did any of these issues become things that you wanted to put into a report, to share either with the provost or the president or the Board of Trustees, talking about the overall health of the student body?

BRENNEN: The honest answer is no. I didn't want to make the problems worse, and there was, it seemed to me, very little chance that anyone other than my close colleagues, whom I've just mentioned, would even begin to understand the problem. I think most of the faculty were of the same opinion that I had prior to my involvement, namely that these were all good kids, high-performing kids, so they must be high-performing not only academically but also personally. That wasn't the case.

ZIERLER: Would you have a sense of, during your time with such awareness of this, have these issues always been a challenge for Caltech? Do you think that they were particularly acute just by virtue of when you happened to be master?

BRENNEN: Hmm, that's a good question. First let me comment that I don't think Caltech was unique at all. In fact I was very proud of the support system that I created with the resident associates and myself and the deans and so on. We were proud of the support system we generated, and we doubted that other places had that kind of support system. We didn't doubt that every other university had the same kinds of issues at that time, for example when LSD was doing the rounds of student communities. I mentioned it, of course, to the higher administration, but I also didn't want to overstate it, because then the faculty would say, "Well, we've got to close down the student houses." There was not much sympathy for the students, if you like, among either the administration, the trustees, or the faculty.

ZIERLER: What do you think accounts for that, culturally? The lack of sympathy, as you explained it.

BRENNEN: Lack of sympathy is probably putting it too strongly. They just weren't aware of the problems. They weren't aware of the student culture, the youth culture, and they didn't really want to know much about it. They felt uncomfortable with it. Going back to my upbringing, I had seen community problems particularly in Northern Ireland with all the violence and with the problems within the society there. I didn't feel intimidated by these problems the way other faculty seemed to be.

ZIERLER: When the opportunity to become dean of students arose, what experiences from being master of students informed your decision to take on this new role?

BRENNEN: I knew what I was getting into when I was asked to be dean. I also realized that it was less trying to be dean, because as dean, you get home at 5:00, and you didn't have the same kind of demands on your time in the evening. When I was master, I lived on campus, in Steele House, so I was right there. I'll tell you a little bit about what happened there, too, a little later, and it involved my wife. We would provide special dinners for groups of students almost every Sunday. My wife would arrange for a Chinese meal, or an Indian meal, to be delivered to the house, and we would entertain usually as many as 20 or 30 students to dinner each Sunday night. Or Saturday night; I can't remember which it was now. It really was a complete family involvement in the affairs of students. Being dean, I lived in my old house back in Sierra Madre. It didn't have the same impact on my life at all, or my kids. The schedule was much more a common work schedule. It was much less demanding on my time and much less demanding on my family. There was a significant difference. I thought I could do four years as dean without the same kind of impact on my family that there was when I was master.

ZIERLER: When you lived on campus, did your family live with you?

BRENNEN: Yes, my family lived with me, in that house. It's called the Steele House, and it's now where the Applied Math Department is housed. A nice, big house. We enjoyed the house. It used to have a swimming pool in the backyard, so we enjoyed that, too. But that didn't really make up for the negative impacts. I have to make the picture a little clearer by indicating that there were a number of occasions in which there were physical threats to myself, and therefore inevitably to my family, by living there in the Steele House. On one occasion—and obviously this is all nameless—a very deeply disturbed student crashed through my front door and attacked me. In fact, it was only with some difficulty, and because of my background as a rugby player, that I was able to subdue him and hold him on the floor while my wife called the police and campus security, who eventually came and took him away.

ZIERLER: Oh, my goodness. What was this about? Was there some misunderstanding?

BRENNEN: No, he was just crazy. Just crazy! He had imagined me as the devil incarnate, if you like, for reasons that are almost irrelevant to relate. He was one of the more deeply disturbed psychiatric cases that I had to deal with. It wasn't just me, because my wife was terrified by that. My daughter and my son were both there. My son fortunately stayed in his room upstairs, didn't really see this. My eldest daughter climbed the fence and ripped a great gash in her leg in trying to get away from the house on that occasion. One of the things I want to say, since I have mentioned that incident without any names of course—the person who first got to the site was Gary Lorden. I've always been intensely grateful for Gary for the way he dealt with the situation, came to the place without really knowing what was going on, and managed to help me resolve the situation that night. That took guts on his part, and it took compassion on his part, for both of which I remain and have always been incredibly grateful.

ZIERLER: Was Gary coming simply as a friend and a colleague or did he have an official role to play here?

BRENNEN: Gary was the dean at that time.

ZIERLER: Oh, I see. You succeeded Gary as dean.

BRENNEN: That's right. Yes, I did.

ZIERLER: How does this work? Does Gary ask you, or does he recommend you to succeed him? Are you chosen by the president or the provost?

BRENNEN: The choice was made by a special committee set up to choose the dean, just as there was a special committee of students and faculty set up to choose the vice president for Student Affairs, or even at that time the master of student houses.

ZIERLER: The vice president for Student Affairs and dean of students, obviously those are two separate positions?


ZIERLER: What are the differences in their respective portfolios?

BRENNEN: The dean dealt with academic affairs pertaining to undergraduates. The vice president for Student Affairs had charge of all of the student offices, from the Registrar to the Athletic Department to the Music Department, et cetera. I think it was something of the order of 150 people. He was really the person in charge of the personnel who serve students.

ZIERLER: When you accepted the position as dean, what were the most important issues for you to focus on?

BRENNEN: I need to break that down a little bit. Of course I continued to deal with student problems. I knew by the time I finished as master that there were some problems I had to continue to address, along with whoever was master or beyond. One was that in the area of academic affairs, it was the tendency of students to overload themselves, which in turn would lead to some of the drug problems, which would in turn lead to some of the antisocial behaviors. Students had a remarkable ability to think they could do more than they really could. There were exceptions, but many students would consistently overload themselves instead of focusing in on some basic subjects and learning the stuff thoroughly. That was one particular issue. Coupled with that was the fact that in certain departments, the requirements for graduation were, in my mind excessive, and I did work to try to make those more reasonable and allow the students more flexibility to pursue things like research with a faculty member. I was a great supporter, and still am, of the student summer research program. That led students to many opportunities after their time as students that they wouldn't have had otherwise. Those are just some of the problems that occur to me, in that domain.

ZIERLER: I want to ask a few questions—maybe they happened when you were dean or elsewhere, but just the general theme of admissions policies at Caltech. If you can give an overall primer, from your perspective, for admission to Caltech, what is it that Caltech is looking for?

BRENNEN: That has multiple answers depending on who you ask, obviously. I think most of the faculty are looking for someone with a genuine interest in science, and ability in math and physics and chemistry, to pursue that academic program. Obviously we are looking for ability in basic science and math. We also look for some sense of breadth and curiosity. Curiosity, and interest in what they are doing. That was also something you tried to measure, tried to evaluate. Incidentally, I was a member of the admissions committee before I became master. So I already had some insights into that whole issue, and felt that we needed to be careful, too, during admissions, that a student wasn't being driven by his parents. Again that comes back to another form of abuse that our incoming students might have suffered from, parental pressure. Parental pressure to go to Caltech. My goodness! When I was interviewing students prior to their admission, I would sometimes ask them, "Do your parents want you to go to Caltech?" The answer would be very interesting. For me, the most important answer that they could give was, "My parents don't know anything about Caltech." That was a plus for me! Parental pressure was an issue that I dealt with both as master of student houses and as dean.

ZIERLER: What about the ability to assess students' likelihood to become future leaders in their field? Could you get a sense from a high school student filling out an application who would go on to positions of leadership?

BRENNEN: Not really, no. Many students have only begun to understand dimly their own interest in science, or even begin to understand what area of science might be of greatest interest to them. That evolves when they are undergraduates. No, we didn't see much of that. I would always look for students with real initiative, in whatever areas, whether they were in the Boy Scouts, or Girl Scouts, or they were interested in and very accomplished in sports. Not that we got too many of those, but—when a student was multifaceted, I felt that their psychological well-being was more able to deal with Caltech.

ZIERLER: For your service on the admissions committee, as master, as dean, when did Caltech start to think about the importance of—and I'm not even sure what the right term is at the time—minority admissions, or diversity, or affirmative action? Whatever the term of art at the time was, when did Caltech really start to embrace the importance of diversifying the undergraduate student body?

BRENNEN: Caltech embracing it? I don't know that I can say that. I know that there were many of us right from the beginning who were very anxious to improve the diversity, improve the percentage of women in the undergraduate class. Those numbers were very dismal when I first got involved as master and of course have radically changed since then. I think we were all anxious. But Caltech had such a reputation as an all-male school that it was very difficult to increase those numbers, particularly among minority students. As you may not know, I chaired a committee on the admission of minority students. We wrote a report as to ways that Caltech could improve minority admissions. We had an old system that was very inefficient of sending faculty members out to high schools to interview. I was a part of that when I was on the admissions committee. I would go out to high schools in the Bay Area, and in Hawaii and in Southern California to talk to students. That was very effective, I think, in a couple of ways. It was effective in identifying students that would be successful at Caltech and would improve the student diversity at Caltech. It was also impressive to high school physics and math teachers when a professor from Caltech would show up to interview them and interview their best students. But that was such an inefficient process that it got discontinued somewhere in the middle of my time in student affairs. I still regret that, because it was in some ways a very effective way of directly improving diversity.

ZIERLER: Maybe it's an obvious answer, but it should be answered regardless. Why is it self-evident that it's good for Caltech to diversify its student body? Why make the emphasis on improving numbers as they relate both to gender and racial diversity?

BRENNEN: Because we play such a large part in the science policy and science of the country, and there's such a dearth of minority, and at that time women, scientists, that it was very important, I thought, for Caltech to play its part in rectifying and resolving that situation.

ZIERLER: You said it was difficult particularly for minority admissions. When you did make a successful admission, what did you find was the winning formula to get a minority student successfully onboarded at Caltech?

BRENNEN: Personal contact—always personal contact—and much more important for minority students, who felt they were coming into a strange, foreign land at Caltech, so having someone that they actually had talked to about their personal objectives was very important. That became clear to me. That's one of the reasons why I think when we stopped sending faculty out to high schools that that had negative effect on minority admissions.

ZIERLER: Of course that's just one half of the battle, getting minority students to Caltech. Then of course you have to support them for a successful undergraduate experience. What did you learn in that regard?

BRENNEN: Again, same thing, understanding of their feelings of finding themselves in a minority situation at Caltech. I felt with some of those students it was very important for me to point out that I had been myself discriminated against and felt to be in a minority. A Northern Irishman at Oxford was certainly a minority. There was an aura of negativity associated with being from Northern Ireland. And at that time, I could not disguise my accent.

ZIERLER: Tell me about the Brennen Report on Minority Admissions. How did that come about?

BRENNEN: I can't remember which president set that up, whether it was Tom Everhart or David Baltimore. Whichever it was, they asked me to chair a special committee to look into minority admissions, and I was very glad to have that opportunity. I thought it was a very important thing to do. We had good representation of minority students, graduate students and undergraduates, on that committee. We had some tough conversations in that, and that was good. Conversations about how they felt, and what it felt like when they came to Caltech, what it felt like for them to experience discrimination at Caltech. I can't really point to examples. There were, however, some cases in which their presence was regarded as suspicious by some of our security staff, for example. That was a problem that arose a number of times. They were usually quite reasonable men and women on the security force, but their expectation that any Black young man on campus was there for no good purpose, I think that was a real problem.

ZIERLER: Did the report issue recommendations? Who was it directed to?

BRENNEN: To the president. The president set up that special committee. I presented the results at a faculty meeting also. It was David Baltimore, I believe, who decided to try to enact some of the recommendations that we made in our report.

ZIERLER: Do you remember what was enacted or what policy changes occurred as a result of the report?

BRENNEN: It's becoming a distant memory to me now, so the specifics are hard for me to point to. We made it very clear that improving the number of minority students on campus was essential. It had to reach a number where individual minority students felt they had friends and companions around them who could sympathize with them and to whom they could turn for help if needed. So, improving the admissions was the most important thing.

ZIERLER: When it was time for you to step down as dean, what were you most proud of? What had you implemented or even changed culturally for the better at Caltech?

BRENNEN: That was one area that I felt I had been able to contribute. But it is very hard to find specifics in other areas. You get so involved with individual problems. Of course, what I remember most as master and as dean are the number of students whose lives I saved, I think, by intervention, in various ways, and at various times. There were other lives that were lost, regrettably. That's my biggest regret, when I think of the short list of students who died while I was in those positions. That's a great regret.

ZIERLER: It really underscores just how important and serious the position is, how high the stakes can be to do it right.

BRENNEN: Absolutely right. Perhaps I'm proudest of that—every time I would go to graduation ceremonies and one of those young people, whatever their racial background or sex, happened to go up, pass by on their way to get their diploma, and I realized that I had perhaps saved their lives.

ZIERLER: Have you kept in touch with any students over the years?

BRENNEN: Oh, yeah. There are a number of them on Facebook, for example. Not the ones that were in trouble, really, but mostly ones whose company I very much enjoyed. Of course I would take them on hikes in the San Gabriel Mountains, particularly Dabney House, because of my special relationship with Dabney House. Every summer, we would have a Dabney hike where they'd climb down a canyon and swim through pools and so on. That was great fun, to be with them.

ZIERLER: A great bonding experience and probably a great way for them to blow off some steam, too.

BRENNEN: Absolutely. Yes, indeed.

ZIERLER: I want to round out today's conversation by focusing on your next position, when you were EO, executive officer, for Mechanical Engineering. The first question there is, after eight solid years of all of this administrative responsibility and all of the administrative stress—of being master, of being dean—didn't you kind of want to just go back to being a regular faculty member at that point?

BRENNEN: I did, essentially. This was easy stuff compared to the others. There were some faculty hires that took place under my auspices. Whether it was as executive officer or just before, I can't quite remember. I'm very proud of the young faculty whom I helped to hire to Caltech and did change the makeup of the faculty a little bit. I'm thinking of people like Melany Hunt and Tim Colonius and other junior faculty whom I helped to hire.

ZIERLER: You've alluded to the position, what's required of an executive officer, but let me ask more directly, what does it mean to be an executive officer? At the time, of course, EAS did not have departments; it had options. Was executive officer kind of like a department chair, or how did that work?

BRENNEN: It was very easy compared with administering the whole of Student Affairs. I was back with my friends in the faculty. I had a large number of contacts within Mechanical Engineering to help deal with it. It was just arranging the courses, making sure that the course schedules were appropriately taken care of, dealing with other minor problems. About that time I started to realize that we needed to renovate the Thomas Building, so in very early times I got involved in planning that renovation, even drawing up the plans myself of what the Thomas Building might look like. That was fun, because I got to meet one of my boyhood heroes. Maybe I've told this story before?

ZIERLER: No, I don't think so.

BRENNEN: When I was a kid, I just loved following Grand Prix racing. I loved cars, and them racing around a circuit. At some point, I realized that one of my boyhood heroes, one of the drivers that I followed when I was a 10-, 11-, 12-year-old kid, was Jim Hall. Jim had been a student at Caltech. He was a graduate of Caltech! Much to my delight, I was given the assignment by one of the fundraisers of getting to know Jim Hall. I played golf with him out in Palm Springs and so on. That was tremendously exciting. In fact, I was able to bring to him this boyhood autograph album that I had collected when I was a kid to show him that I had diagrams of his invention of foils, and also his invention of the vacuum cleaner that would suck the car down on the road. That was banned after a very short time, incidentally. Jim learned his fluid mechanics at Caltech and applied them to worldwide motor racing objectives. It was real fun to meet and get to know Jim Hall. Later, when Jim was inducted into the Motor Racing Hall of Fame, he invited me to go along as a guest of honor of his, at that Motor Racing Hall of Fame ceremony, where I got to meet a whole bunch of other drivers, people like Carroll Shelby, and Roger Penske, and other famous motor racing drivers of the United States. That was a pretty awesome experience, I must admit.

ZIERLER: You mentioned the importance of renovating Gates. Was it essentially original from the time it was constructed?

BRENNEN: Yes, renovating the Thomas Building. It's now called Thomas-Gates, isn't it, but in my time, it was the Thomas Building. Yes, it was one of the original buildings on the current campus and really was long overdue for renovation. They did a marvelous job of it.

ZIERLER: These were renovations of lab space, office, and classroom? The whole building?

BRENNEN: The whole thing. They just emptied it out and started again.

ZIERLER: Was there a building campaign? Was there a funder who made this all possible?

BRENNEN: There were several of them, and Jim was one of the ones. If you go to the back of the Thomas Building, the new auditorium sticks out from the back of Thomas Building. It's a lovely auditorium and Jim Hall funded that. There were a number of other donors who funded that renovation. I've got to tell you, though, from my point of view, the other neat thing about the Jim Hall Auditorium. If you look at it from the outside, at the glass surrounding it, you'll see that there's a picture of a cavitating foil, etched in the glass. If you haven't seen that, you should. It's etched on the exterior glass of the auditorium, so that's very neat.

ZIERLER: Oh, wow, I'll check that out! That's great. Going back to the faculty after all of those years, how much catch-up did you need to play in terms of the material, in terms of teaching? Were you able to keep up your research program or did that really have to take a back burner?

BRENNEN: I really was able to keep it up, but only because of the generosity of time and effort of my colleagues, specifically Allan Acosta, Rolf Sabersky, Melany Hunt. All of them contributed, as colleagues, to maintaining my research program. I had also gotten better by that time at knowing how to advise graduate students. That was something that to begin with was a bit of a puzzle to me, how you taught graduate students, what was the best way to improve their functionality as a researcher. It wasn't like teaching undergraduates; you had to teach graduate students to think about new things, and to have new thoughts, not old thoughts they could look up in a book.

ZIERLER: I mentioned earlier that Caltech has options and not majors. In EAS, were you part of the conversations to transfer to a department structure, or that came after your time?

BRENNEN: It kind of came after my time, but we all recognized that we needed a more coherent structure in the part of Engineering that was housed in Thomas. Previously there had been these little groups that were seemingly independent, didn't have much influence with the larger administration, didn't have a very coherent program of improving the faculty, improving our teaching efforts. So that consolidation, reorganization, I thought was critical. It had been in the works for quite some years. I had talked to people like Paul Jennings about it many times in the years past.

ZIERLER: The fact that EAS does have departments now and other divisions do not, is that simply in recognition of how large EAS is, how it's such a complicated division relative to the others?

BRENNEN: Yes, it's such a diverse division and such a large division. It reflects that, I think.

ZIERLER: Another administrative question, unrelated—nowadays Caltech does not have the associate professor designation. When you get tenured, you go from assistant all the way to full professor. Were you part of those conversations as well, or do you have any commentary as to why that decision was made?

BRENNEN: No, I think it was after my time. I was a bit surprised by that, but it didn't seem to be inappropriate. We knew at the time that Physics, for example, had that new structure in effect, but Engineering did not. I don't know that it mattered a whole lot. The important thing was whether you got tenure or not.

ZIERLER: The last thing I want to focus on today, of course, is let's get back to the research. It's great to hear that you were able to keep up your research during your time as both master and dean. When you went back to the faculty and you had more bandwidth, what was important for you to focus on at that point? This would have been in the early, mid 1990s. What were the things that were going on that you could devote more attention to now?

BRENNEN: First and foremost, I had to recover from all those years. I had to get my own foundation back. I had to spend more time with my family. My wife and I went on sabbatical. We spent a very nice time in Oxford. Then I went on a special extended visit to Japan. My wife chose not to go with me at that time because of other family issues. I think getting my balance back and trying to figure out where I was going to go, it took me that year to really get to that. Then of course I was asked to be vice president for Student Affairs, and that's what David Baltimore wanted, and so I said, "Okay, I'll do it again."

ZIERLER: Tell me about returning to Oxford. What was that like for you?

BRENNEN: That was lovely. We took time to go to concerts. We went on walks. We visited our family, of course, which was not far away in Northern Ireland. Both of Doreen's sisters at that time lived in England, so we were visiting family, and having time together, Doreen and I. That was very important. When I look back, of course it's doubly important given Doreen's early death, which was the second of my great tragedies, which we haven't really touched much on, but were then not too far away.

ZIERLER: I wonder if you noticed any cultural changes at Oxford, when you related your own personal difficulties from Northern Ireland. Had things changed at all since the time you were an undergraduate? Did you have any sense of that?

BRENNEN: No, not much, really. [laughs] To be honest—see, way back—jumping way back now, I had interviewed for jobs at Oxford. I had failed to get those jobs. More than that—this is much earlier—not only had I failed, but I recognized not too long after that that the individuals who got those jobs instead of me were quite second-class. It really seems very arrogant to say that, but they didn't have the kind of research portfolio that I had by any means. I did feel that that was another occasion when my Northern Irish accent was a factor in their selection process.

ZIERLER: Tell me about your time in Japan. What was the invitation?

BRENNEN: The invitation was to tour Japan. I visited many universities and colleges all over Japan. I greatly enjoyed that. It is one of the friendliest countries in the world, the most hospitable. I greatly enjoyed my Japanese hosts there, in particular Yoichiro Matsumoto at the University of Tokyo, and Yoshi Tsujimoto at the University of Osaka. That was quite an exhausting trip they set up for me, where I gave a talk just just every other day at a different university.

ZIERLER: Who was your host? Who sponsored the trip?

BRENNEN: An academic organization called the Japan Society for the Promotion of Science., They elected me a fellow of that organization. One of the responsibilities—and they paid me quite nicely—to go to Japan to give this series of talks. I can't remember how many. It must have been, oh gosh, how many lectures did I give? At each of the places I visited, they were very hospitable.

ZIERLER: Were the talks more focused on your scholarly expertise in cavitation, or did they want to hear more about your administrative expertise from all of your time at Caltech?

BRENNEN: I think I gave maybe one or two of those administrative ones. The rest were all about the various research areas that I was involved in. Most of them were on cavitation.

ZIERLER: What were some of your overall takeaways about the Japanese approach to higher education?

BRENNEN: It was very structured—again, almost too structured—and very effort-intense. The Japanese, whether in education or in their jobs, work intensely hard, to the point where their initiative is squeezed out of them, if I can use that analogy. They aren't given an opportunity to think for themselves, really. Again, there was almost no diversity. I later became an advisor to the University of Tohoku in Sendai, and I tried to impress on them that they needed to hire some women faculty. There were women graduate students whom I encountered who were very good. I don't know that any of them got on the faculty. That was an issue that I didn't hesitate to pursue with them and to talk to them about. I was never quite sure whether they were listening or not.

ZIERLER: When you returned from sabbatical, did you take David Baltimore's invitation immediately?

BRENNEN: Yes, I did, really. I should have given myself a little more time than I did.

ZIERLER: We'll pick up on becoming vice president for Student Affairs next time, but my last question for today, just in the chronology, I'd like to ask about two of the most significant books that you published, in the mid-1990s—in 1994, Hydrodynamics of Pumps, and a year later, 1995, Cavitation and Bubble Dynamics. When you were master and dean, how did you find the time, with all of your other responsibilities, to get these books done?

BRENNEN: First of all, you should recognize that the books are accumulated over many, many years, so many of the chapters, if you like, and sections, had been prepared, sometimes in preparation for a class I was giving at Caltech, or a lecture I was giving. Each of those lectures or classes would form a unit that I would put in a framework of the book. There was of course other stuff you had to put in as filler to connect all these pieces together, but that process of collecting must have taken me—for the book on cavitation, it probably took 15 years of those notes that were put together for that. That's probably the book that I'm proudest of in some ways.

The book on pumps had a slightly different origin. I had been asked as a consultant to give talks for a friend of mine who had a pump company up in New England. I had prepared notes for those. I had also been to India where I prepared notes on pumps and turbomachines for my stint in India at the Central Water and Power Research Institute, in Khadakwasla, outside of Pune, where I spent a month or so. All of these lecture notes fitted particularly into the pump book. At some point, David Japikse, who was head of that company in New England that I gave these talks to, said, "Why don't you write up these notes?" No, he was smarter than that. He said to me, "Chris, I'd like to record your lectures the next time you're up here giving these lectures." I said, "Oh, all right, okay." He continued, "I will have someone write down what you said." A few months later, I get this collection of garbage from him, which were the things I said in the lectures, only barely making sense at any point, because anytime you transcribe someone's lecture, it really does look pretty much like garbage. So, I felt absolutely obliged to go through and correct the language. That's what began this book. He then said, "All right, we're going to publish it in a book." That's how the pump book began. Actually it came out earlier because of all of the pressure from my friend David Japikse to get that project finished. The origins of the cavitation book came much earlier.

ZIERLER: What's the thinking behind publishing a book? Is there a gap in the literature? Is this an opportunity as a teaching tool to provide a textbook where everything is in one convenient place?

BRENNEN: Yes, I think the latter is certainly the case. My books have always been essentially academically oriented though they've been widely used in industry—both the cavitation book, the pump book, and these days to a great much greater extent, the Fundamentals of Multiphase Flow, which was a book that took quite significantly longer to put together and contained a much wider set of subjects. Once I got started on those books, it was natural to continue on. Pieces of the cavitation book are in the book on multiphase flow. Pieces of the pump book are also in Fundamentals of Multiphase Flow. There was a lot of overlap between all those three books.

ZIERLER: You mentioned how proud you are specifically of the cavitation book. Is that because just of how widely it has been used both in academia and industry, just the impact that it has had?

BRENNEN: Yeah, I suppose, but more importantly, I'm proud of it because I spent a lot of time and effort on it, and I think I contributed significantly to improved presentation of the subject of cavitation in that book. The pump book was a more practical book that doesn't have quite the same impact, I think.

ZIERLER: Have you ever considered updating the books, or have they more or less stood the test of time?

BRENNEN: No, I'm not interested in updating them. That's a huge task that just would be impossible given how much has been done since the books were published.

ZIERLER: Last question for today. I know it was too soon—you would have given yourself a little more time if you had the option—but when you were asked to become vice president for Student Affairs and you said yes, to what extent is that simply a statement of loyalty to Caltech, that when you're asked to do something, you step up and serve? I wonder how you see it in those terms.

BRENNEN: Good question. I really hesitated before I became vice-president of student affairs, because I had already impacted my family significantly by that point. I probably shouldn't have taken on that job, because I think it continued, to some extent, to impact my family. Now we get into serious business associated with my son's death, my first wife's subsequent death, and, as I mentioned to you before, my feeling of guilt of maybe I could have done more, to take care of them, while they were alive. It's a terrible thing to say, but I have to be honest. My current wife Barbara would say, "No, you did the best you could." But I'm not sure that I did.

ZIERLER: All I can say is thank you for sharing honestly how you reflect on such difficult times.

BRENNEN: I certainly think about them both all the time. My son, of course, we haven't talked in detail about my son, but he was a unique individual. It's only after his death that I look back and realize what he was able to do in the very short time he lived. He became a world-class skateboarder, someone who contributed to the sport of skateboarding in a way that I never imagined was possible. Now, when I look at the Olympic competitions, skateboarding competitions, I recognize what he was able to do, and what these young people now are able to emulate. If you look up Pat Brennen on Google—Pat Brennen, the skateboarder—you will get an impression of his impact. On one of my much later visits to Australia, Barbara and I went into a surfing shop in Perth, in Western Australia, just to see what they had. I saw some skateboards, and I asked one of the attendants in the shop, "Did you ever hear of Pat Brennen?" And he knew all about Patrick.

ZIERLER: What were his contributions that they were felt all the way in Australia?

BRENNEN: Oh, just the uniqueness of his skill in manipulating the skateboard, and performing tricks that no one else did. Then he made these videos with Powell Peralta, which was the company that he skateboarded for, a company down in Santa Barbara. The videos went over the world, where people would see him perform these tricks and try to copy them. That's obviously how this individual in Western Australia had known of him. At the age of 23, that was quite an accomplishment. I did not give him credit for it while he was alive. I didn't really know what he was doing. I regret that.

ZIERLER: The fact that he was able to have this influence, before YouTube or social media, is even more incredible.

BRENNEN: Yeah, it was the distribution of the videos that Stacy Peralta put together. That was one of the co-owners of that company, Powell Peralta. He and Patrick were friends, and he and Patrick would go off at all times of the day or night to make videos in downtown L.A. and elsewhere. Prior to doing the skateboarding videos, Stacy became well-known for taking videos of rock climbers.

ZIERLER: Thank you for sharing your son's legacy with me. I really appreciate it.

BRENNEN: It's a remarkable legacy—we still see, on YouTube, tributes to Pat Brennen.

ZIERLER: That's great. Chris, next time we'll pick up in 1998, when you become vice president for Student Affairs. We'll continue the story there.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Tuesday, October 24th, 2023. It is wonderful to be back once again with Professor Christopher Brennen. Chris, as always, it is a great pleasure to be with you. I'd like to thank you so much.

BRENNEN: Thank you, David.

ZIERLER: The year is 1998. You come back. Now, do you know you're going to take on this new position as vice president for Student Affairs after your sabbatical?

BRENNEN: No, I did not. I didn't know until the last minute, I think, when David Baltimore called me in and asked me to take the job.

ZIERLER: Did you have a relationship with David? Did you know him well? Did he appreciate all of the concern and expertise you had for the student experience?

BRENNEN: I would say no to that, all of those questions.

ZIERLER: Basically you must have been recommended to him?

BRENNEN: Yes, obviously, I think that was the case.

ZIERLER: Any idea who would have nominated you?

BRENNEN: I don't know, but my guess is it would have been some combination of Gary Lorden, David Wales, Jim Morgan, as well as my other faculty friends and colleagues.

ZIERLER: Obviously, it's a question I'm sure that you've reflected on. It's one about loyalty to the institution. It's about giving the best of yourself. Why not just fight the impulse and say no? After all that you had gone through, all that you had experienced, at this stage in your career, did you consider saying no, or was it just sort of not in your constitution?

BRENNEN: I did consider saying no, and I talked it over at some length with my wife at the time, Doreen. I don't think she was very keen on it at all. She had had enough of me heading off in the middle of the night to go to meetings or deal with individual students. I don't think she was keen on it. When I look back, it was not a particularly satisfying position to have, really, just administering a staff of 150 staff members in Student Affairs, and also dealing with some student problems that were brought to me by the dean or the master. If I was to go back again, I would probably say no. I will admit to that.

ZIERLER: It does beg the question, then, why you said yes.

BRENNEN: I had so enjoyed the contact with the students. The most difficult of the positions I had was being master of student houses. I dealt with some crazy situations! But I got a certain pleasure from that. I've always been a rock climber, a person who took risks, and I would get self-satisfaction from taking and overcoming those risks. Also when I look back at the students that I helped as master or as dean, I took great self-satisfaction at what I was able to do for them. None of those things really were true of being vice president for Student Affairs. If I was to do it again, I probably would say no. Unless someone said, "We really need you to do it," in which case I would have been tempted. I think that's what David Baltimore said— "I really want you to do it, Chris. You're the person with the most experience in this job." That sums it up, really.

ZIERLER: Administratively, Chris, what organizations, what offices, fall under vice president for Student Affairs?

BRENNEN: It may have changed since my day, but there was the Music Department, the Drama Department, the Athletic Department—a very large athletic staff—Student Aid, the Dean's Office of course, the Master's Office, the Registrar's Office. The job opportunities office; I forget the name of it now. All of them were under the auspices of the vice president for Student Affairs. I had a good staff who for most of my time there—well, for all of my time there—were really very knowledgeable about administering that office. I don't see how I could have done that job without that staff. Stan Borodinsky knew everything about the Institute. If I needed to know who was where, Stan would know! Stan was the man! I enjoyed him. He had a wry sense of humor. He didn't take himself too seriously. So, I got along well with Stan Borodinsky. And Sharon—what was Sharon's last name? I forget their last names, of course. Then later on, Barbara Green was a great person to work with. I still communicate with Barbara Green from time to time. Lots of very nice and dedicated people.

ZIERLER: The extracurricular activities for Caltech students—the arts, the music program, the drama program—as dean of students, did you recognize how important these were as a pressure release, as an outlet for students?

BRENNEN: Absolutely! I tried my best to improve those opportunities. When I became vice president for Student Affairs, I formed a committee to study the structure of those components of Student Affairs. That was quite a very valuable effort. I asked Steve Frautschi, an old faculty friend, to chair a special committee, and he made certain recommendations to me about the structure of the art programs and the drama programs and the music programs. I took all of those. I made all of the chiefs of those activities adjunct faculty members. They were so pleased just by knowing that they were called now a faculty member. That was a great boost, I think, to their morale and their activities.

ZIERLER: Tell me what was most important for you in terms of the overall responsibility as vice president for Student Affairs. Did you have a mission, were you mostly responding to external events, or both?

BRENNEN: No, I don't think I was responding so much to external events, though they obviously affected me. No, my mission was to improve the quality of life for students and the academic experience for students. Those two aspects of student life were what I felt I was charged with improving, enhancing, and adding to, in some ways.

ZIERLER: How do you work that out from a budgetary perspective? Are you always advocating for more funds for certain programs?

BRENNEN: Not always, and not just that. I also advocated for more faculty involvement. I learnt in my early days at Caltech, my interactions with Richard Feynman and other notable faculty members, that interacting with them was a great boost to one's intellectual achievements and desires.

ZIERLER: What was most important for the extracurricular activities? What did you need to do to enhance, as we were just discussing, that students knew about these programs, that it was important for them, that if they wanted this outlet it was available to them?

BRENNEN: I was always advocating for their involvement in those activities. I didn't mention one of my other prime responsibilities was the health center, both the medical side and the counseling side. I felt very strongly from my earliest days that that was very important. Of course I had already by then had significant experience dealing with the health center and with some of the members there that were really truly dedicated to the students. I remember with great sadness Bruce Kahl, who died in my early days of being involved with Student Affairs. He was a great counselor. So were the other counselors. And my great friend, Stuart Miller was the head of the medical side and was very dedicated and very responsive to anything that I would ask of him. My personal relations with all of these people were really crucial in making things move forward and in finding out about problems before they became critical.

ZIERLER: Do you think from your previous appointment as dean of students that that was an asset as vice president?

BRENNEN: Oh, yes, of course! It meant that I knew a good deal about student affairs. I knew where all the weaknesses lay, I knew where all the strengths were, and I needed to do my best to address both of those.

ZIERLER: We talked in a previous conversation about your involvement, your efforts to make the undergraduate student body more diverse and more inclusive. Did you continue in that role as vice president for Student Affairs?

BRENNEN: Absolutely. That was another very important objective, to broaden the experience for the average Caltech student by having a diverse undergraduate and graduate body. Of course the graduate body was always more diverse, but the undergraduate body was far from diverse. I tried to do my best to both attract and retain minority students among the undergraduates.

ZIERLER: How did you translate those goals within the admissions committee? Ultimately, of course, the admissions committee are the gatekeepers for who is admitted. Do they also play a role in terms of attracting a more diverse student body?

BRENNEN: Yes. There were also certain individual staff members who would go out and interview some of the prospective minority students. That was a crucial part. I think in general, the faculty were all quite committed to this objective, to increasing the number of female students, to increasing the number of minority students, and to ensure some kind of balance of the American population within Caltech.

ZIERLER: Does the SURF program fall within the vice president for Student Affairs portfolio?

BRENNEN: That's a good question, and I don't know that it ever did, really. It seemed to be separately administrated by a SURF committee, a faculty committee, whose job it was. I was still involved with the SURF program. I addressed the SURF students almost every summer at the start of their stay at Caltech. Sometimes these administrative connections don't need to be as set in concrete as they—you could influence things even though you didn't have administrative responsibility for them.

ZIERLER: The broader question is if you had opportunity to foster student opportunities at JPL. Was this something that was available to undergraduates? Did you work to enhance those opportunities?

BRENNEN: Certainly through the SURF program and extensions of the SURF program, yes, that's right. But there were other faculty who addressed that kind of connection. It was among my priorities, but it didn't have to be a priority because there were so many other faculty who had a direct interest in creating research opportunities for undergraduates, both on the campus and at JPL.

ZIERLER: You conveyed well in a previous conversation just how all-encompassing your responsibilities were as dean of students, of course the impact that this had on your family but also on your research agenda. What about as VP for Student Affairs? Were you able to keep an active research group?

BRENNEN: Oh, yes.

ZIERLER: Were you able to publish?

BRENNEN: Oh, yes. If you look at my publication list, you can see that it didn't ever really dip during any of these times. It continued to grow and I continued to be asked to give talks at places all around the world.

ZIERLER: This was still your main interest where you were still working on cavitation?

BRENNEN: Well, cavitation, yes, but also I worked in a number of other research areas which really weren't connected. The one thread that connects them is I dealt a lot with small things in fluid environments, whether it be the swimming of microorganisms, the flying of birds, the swimming of fish. All of those were things that interested me. I was also interested in sand particles, and how huge groups of sand particles would all collide with one another as the sand flowed. Numerous small things were part of my interest during my career.

ZIERLER: One service appointment I'm curious about is when you served as editor of the Physics of Fluids component for the American Physical Society. Tell me about that, what that involved.

BRENNEN: There were a number of editorial jobs that I took on, some very temporary. I didn't much enjoy that. I enjoyed reading the papers. I didn't enjoy the hassle of telling authors that we couldn't publish it, or that they had to modify most of their text. I could see that others did that better than I did, and it really wasn't my kind of thing, so I didn't really do as good a job in those positions as I might have.

ZIERLER: A historic day, a tragic day, that occurred during your time as VP for Student Affairs of course was September 11th, the terrorist attacks on the United States. What was that day like for you? What was happening on campus that day?

BRENNEN: The whole campus was really in a state of tremendous shock, of course, and there was a real danger that there would be repercussions that would be overreaction—and that's a situation that worries me now, with the issue of what's happening in Israel and Palestine. The overreaction, the desire to "go get ‘em," which didn't do us any good in the aftermath of 9/11 and won't do us any good today. I remember in particular there was a student rally at which a number of us made talks—Marianne Bronner-Fraser was one of the faculty members that was involved in that, and I was—in which we tried to urge caution, tried to urge the students—I remember the meeting outside the bookstore in the middle of campus—we tried to urge students to try to not overreact to this situation, overreact by punishing Arab citizens of the United States or anywhere else. That's what I feared, a real vicious reaction to 9/11. 9/11 of course was awful, nothing could ever excuse that, but the reaction can be almost as bad if one is not careful. What was interesting is I felt that I had connected with the whole group of students who gathered there that day, and I still have the video that someone took of my presentation there. What happened after that talk, in the next few days, was I got several awful hate messages, not from anyone on campus that I remember, but of members of the community, and in particular one man whom I knew was a Pasadena police officer, which was really horrendous, I thought. I didn't do anything about those letters or messages. I laid them aside, recognizing that some people will react in that way.

ZIERLER: International students, in the wake of 9/11, were some of them in crisis, particularly those who came from the Middle East?

BRENNEN: You bet. You bet. I can't remember specifics. There were certainly students, both undergraduate and graduate students, who were in a crisis then, as is the case in almost every great tragic event that occurs. That's where the counseling center was very helpful. They would send out messages to the resident associates, to the students, telling the students that if they wanted to talk about what they were feeling, they should feel free to talk to anyone in Student Affairs and to the RAs. I haven't mentioned the RAs enough in this discussion. I just felt they were the first line of defense in dealing with these kinds of issues, student issues. There were some marvelous graduate students—they were almost all marvelous—who dealt on the front line with student problems, people like Andy Dowsett in Dabney House. I am a great fan of them, and of other people who served. My own graduate student, Mark Duttweiler, who was a resident associate in what used to be called Ruddock House. I've forgotten what it's called now. So, yes, there was an unofficial web of support for students, both graduate and undergraduate, though I think more for undergraduates. Actually one of the things that worried me was that there wasn't the same integrated network of support system for the graduate students as there was for the undergraduates. The network for undergraduates consisted of the RAs, the dean, the master, and some other concerned faculty members. That was a very effective network in dealing with undergraduate problems. There was nothing quite like that for graduate students. That's one thing that did concern me and gave me thought as to how to improve that. There were of course advisors for all the graduate students, but the advisors were in many cases just for academic purposes.

ZIERLER: The idea that administration leaders in times like this feel a need to speak out—you mentioned, of course, the current crisis in Israel and Palestine right now, and university presidents across the country, including our own, put out statements where they expressed what they felt that they needed to express. Is that a modern phenomenon? In your time as an undergraduate or in your early career, would university presidents have felt compelled to do things like that?

BRENNEN: The answer is no. That is a modern development. I think what our current president does is most admirable. He's very thoughtful on these issues. In the past, there have been some presidents who haven't reacted quite so constructively as Tom has. I applaud him for his letters to the community, which are also letters to the undergraduates. I find those most helpful, and appropriate.

ZIERLER: What has changed societally where now intellectual leaders like university presidents feel compelled, or that it's in their lane, as we say, to make statements like this, where that wasn't true in the past? What has changed?

BRENNEN: First of all, the lines of communication are radically changed, with the internet and with all the electronic means of communication. That has radically changed and made it much easier to reach out to the students. In my early days, it wasn't easy to reach the students. As I described to you before, the easiest way to reach the students, for me, was to walk around at 11:00 at night and talk to them in groups and as individuals. Much harder to do it any other way back then.

ZIERLER: Tell me about your decision to step down as vice president for Student Affairs in 2002. Is a four-year term a standard period?

BRENNEN: I think so. I was exhausted by that point. I really had gotten to the point where I was suffering from mental exhaustion, really. I simply wanted to find a different way of contributing, which I hope I did, in the years that followed.

ZIERLER: Were you able to take another sabbatical?

BRENNEN: No, not then, because—but it wasn't too long after that, remember, that my son was killed in an automobile accident. That was soul-destroying. That was absolutely one of the two worst things that happened to me in my life. My first wife Doreen never really recovered from that. She neglected herself, and whatever I did, I couldn't counteract that self-destructiveness that she felt in the aftermath of our son's death. She died some years later.

ZIERLER: This unspeakable tragedy of losing your son, did you take a leave of absence from Caltech? Did you want to stay on because it was a respite for you?

BRENNEN: The funny thing is, and maybe it's just self-preservation, that my memories of those days are very dim. I'm not sure whether that's part of my self-defense mechanism, but my memories of the specifics of those days are very dim. Of course I took time off. I took a significant period of months off, thanks to my colleagues again who filled in for me in classes and other things at that time. I went and I stayed with each of my daughters for an extended period. But there's no doubt, when I look back, that the death of my son was soul-destroying. It took a long time for me to somehow reconstruct myself after that, after my son's death and then my wife's death. When I look back now, my current wife Barbara had a lot to do with that process of reconstruction. She was someone that I knew as a young kid and knew all about me. Somehow that helped. It helped me find an emotional home again.

ZIERLER: I'm sure it's a painful question, and it's one that you've considered—what was your son's trajectory? Had he not died tragically that night, where was he headed? What was his life to look like?

BRENNEN: Well, he certainly wasn't an academic, I can tell you that! But he was someone—I see other kids like this—who gets a passion and just pursues that passion regardless of everything else they might be supposed to do. He wasn't interested in academics. He was interested first in racing his bicycle, which he did, and did very well, and then he transitioned to skateboarding and became a world-class skateboarder. When I now look back at the videos of him—and I don't know whether you've had a chance to look at the videos—


BRENNEN: —what he did, he invented all these tricks that were quite remarkable. At the time I didn't really adequately evaluate what he had been able to do. In retrospect, I could have been a lot more helpful to him, I think. Though I did—I remember on one occasion appearing before the Sierra Madre City Council urging them to create a skateboard park in Sierra Madre, because—I said at the time—and I didn't really believe it at the time, completely—but I said to them, in the council meeting, "Someday, one of these kids is going to appear as a skateboarder in the Olympics, and that's what you need this park for." Of course I didn't really think that was going to happen. But now, if you look at the Olympics, my goodness! There's all of this skateboarding, and all these gold medals, all the applause that they get. People like Tony Hawk, whom Patrick knew well, you see him appearing in all kinds of commercials. So there was a real career path that he started to embark on, with his videos, and selling these videos all around the world. So, who knows? I didn't give him credit for it at the time, and I should have, and I regret that, when I look back.

ZIERLER: A happier topic—in these years, if you'll indulge me, there are some major awards and honors that you are given by your peers, by your admirers. I want to cover just a few. The physics and the cavitation community in Japan has really celebrated your career. What's the connection? What is the Japan angle to the kinds of things that you've worked on?

BRENNEN: Oh, I think it began with visitors. In addition to the 32 or 33 graduate students I had, I had always visitors from Japan. I only had one Japanese graduate student right at the end. Before that, it was a better career path for a very bright Japanese student to get his PhD in Japan and then come abroad as a postdoc, so I had a whole series of Japanese postdocs. They were really just like senior graduate students to me. People like Yoi Matsumoto, who became vice president of the University of Tokyo. Like Yoshi Tsugimoto, a brilliant young man who became a faculty member at the University of Osaka. And a number of others, some of whom went to work in the Japanese space business. In fact, one of them is now head of that launch facility at Tanegashima island off the south coast of Japan. There were a whole bunch, and they would feed on the—you'd get one or two to begin with and then others would come, they would all come. I found them all very dedicated as researchers, as students, and very pleasant to deal with, really. Then I started to go to Japan myself, of course, on various visits, when I gave talks all over Japan. I think I made a total of—I counted up once, for a Japanese friend—I said, "I've been to Japan 25 times"—25 times, to give talks, for either a short time, or a long time. That was a very worthwhile addendum to my graduate student research activities.

ZIERLER: These two major awards in 2002 and 2003, first the Fluids Engineering Award given by the Japan Society of Mechanical Engineers, and then the Fluid Science Award from the Fluid Science Foundation in Japan, what were you being recognized for? Was it a separate area of research for each award, or was it more of, all together, a body of research?

BRENNEN: They all overlapped, I think. I was very proud of getting that award from the Japan Society of Mechanical Engineers. I had been given the Fluids Engineering Award from the American Society of Mechanical Engineers, and then I think I was the first to win both awards. Those were the top awards in both the mechanical engineering societies in the United States and in Japan. I was very proud of that award. I don't know that I did anything specific for it. It was for a broad range of contributions to the field.

ZIERLER: What did you learn about the interplay in Japan between basic science and engineering and industrial applications? What did that pipeline look like in Japan?

BRENNEN: It was very much like the American system. I had a lot of contacts with Japanese industry as well—with the pump industry, with the space industry, and, interestingly itself, with Hitachi on the flow of toner in copying machines. That turned out to be a very interesting mini project within this list of things that I did in Japan. As well as hiking many mountains. Both of those friends that I mentioned were hikers!

ZIERLER: Ah! The hiking connection!

BRENNEN: I think Matsumoto and I climbed the highest mountain in Japan—Fuji, of course—the second highest, the third highest, and the fourth highest. Then we couldn't really figure out which was the fifth highest, so we never got around to that.

ZIERLER: [laughs] Of course in 2005, a very special award, the Richard Feynman Prize for Teaching. I want to return, just as backdrop, because you were lucky enough to have known Feynman, did you get a sense of his skills as a teacher, why this award was given in his honor?

BRENNEN: Oh, yes. Richard, to me, was like what I would call an Irish hedge schoolmaster. In ancient times, these bards would travel around from village to village, sitting on the bank on the edge of the road or edge of the lake, and they would give talks to any of the local population that would like to listen to them. They were great storytellers, the hedge schoolmasters. There were some of my ancestors who indeed were hedge schoolmasters. Richard reminded me of them. He would sit on the low wall at Camp Fox on Catalina Island and talk to the new freshman class. They would sit around, enthralled, by whatever he wanted to tell them about, whether it be Mayan hieroglyphics, or Einstein, or whatever. In his books—I always thought this was a little unfair—in the books that have been written about Richard, he comes across as a little bit of a smart aleck. You know, all this business about picking the locks and so on. Yet that's not the way I saw him, or what I felt about him. He just loved to talk and to teach. That vision, that feeling that he was being boastful, was inappropriate. It wasn't part of Richard's character. He loved to talk, loved to teach.

ZIERLER: Did he have, would you say, a teaching philosophy, or this just was a natural gift, that whatever he did just came from the heart?

BRENNEN: I think so. I think it definitely did. He was gifted, with a gift of the gab, like these Irish hedge schoolmasters. He loved to talk. He loved the dramatic, the theatrical, aspect of teaching. You've got to be careful not to act too much, but a little bit of theatre goes a long way in catching people's attention, and that's the important part of teaching—to get people's attention first, before you get across more difficult ideas.

ZIERLER: Of course I'd have to ask others who nominated you for this, but what was your teaching style, and why did it resonate so well? Why do you think you were honored with this great award?

BRENNEN: Oh, I tried to make things, even complicated things, as simple as possible. I didn't want to snow people with fancy mathematics. I wanted them to have a feeling that they understood within their brain what was happening without necessarily fancy mathematics. Then I'd give them a little mathematics to try to fill in the gaps or justify what I was trying to teach them. So, I think enthusiasm. I would always ask the students, "Does that make sense to you?" Some would say no, and then I would try to go back and fill in what they missed along the way. I would always talk directly to the students and never turn to the board and talk to the board. I tried to communicate with them. And, a little bit of theatrical Irishness was always helpful in doing that. As you may have learned from some students, I ended the year—the last class of the year in my fluid mechanics class, I would take them to the Caltech pool to demonstrate to them underwater bicycle racing. I would take my bicycle down to the pool, I'd do a few laps around to get the atmosphere up before I actually rode over the side of the pool into the pool, went to the bottom, and then rode down towards the deep end. At some point, as you could imagine, while in the shallow end, you could get some traction with the bottom by riding a bicycle, but as you went down the slope into the deep end, you would lose that traction, and it was very difficult to get to the far end. I tried very hard a few times to actually make it to the far end. I usually dressed up for the occasion. I would wear a suit and a tie, and one of my favorite hats while performing this clownish stunt. I think there is video of that.

ZIERLER: Oh, I was just going to ask—I'm going to have to track this down. That's amazing. Chris, what phenomenon or what were you trying to teach in this demonstration?

BRENNEN: Oh, we just had fun at the end.


BRENNEN: It was just craziness, yes. I don't think I was teaching anything at that point. But the students seemed to enjoy it. I think the very last time I did it, for which there is some video, there was a whole group of graduate students who showed up, and all of the Athletic Department showed up, for this craziness.

ZIERLER: I wonder if you can reflect on the unique challenges and joys of teaching Caltech undergraduates. Of course, these are students who knew nothing but success in high school, they graduated at the top of their class, they are extraordinarily smart. What are the challenges, what are the pleasures, of teaching students at that level?

BRENNEN: The pleasures are self-evident—their success and everything they did. Part of the challenge was in maintaining their perspective when they didn't end up as top of the class. That was a problem that repeated itself year after year. There would always be some students whose motivation really seemed to be primarily to end up best in the class, get an A, instead of focusing on what they were learning because what they were learning was the thing that was going to matter in the long run.

ZIERLER: This is more as a mentor, not necessarily as a teacher, but what kind of advice would you give students when they were thinking about next steps after college? When should they go on to industry, when they should go on to graduate school. What was the way for you to provide advice without necessarily telling them what to do?

BRENNEN: I think first and foremost, what are you most interested in? What do you like doing? If you choose what you like doing, whatever it is, it's going to be in your best interest in the long run. That's the subject that you'll probably be best at. So, figuring out what you like to do, what aspect of employment you like best, that's the first essential thing. And if you don't like it, you can always change it at some point, also. You don't need to feel that it's a decision which is going to lock you in for the rest of your life. Many of the students that I know of now are all doing very different things in industry, or in teaching, or sometimes way beyond that, in other areas of human activity. Especially I wanted them to feel that they enjoyed some part of what they're doing.

ZIERLER: Of course that same year, in 2005, you're named the Richard L. and Dorothy M. Hayman Professor. What was that like? How do you get that news? What does that mean for you?

BRENNEN: I don't really remember that. I remember getting tenure; that was important. I don't recall who told me I had gotten tenure, but I know that Doreen and the kids were at the pool that day, and I remember going down there, and I remember the embrace of my wife when she understood that we weren't destined to move somewhere else. She enjoyed Pasadena and she enjoyed the Caltech community, and it was a great relief to her to know that we were there for as long as we wanted to be there.

ZIERLER: A named professorship is really, of course, more of an honorific. It's more of an acknowledgement.

BRENNEN: It is, really. I recognized that my predecessors had that same title, and particularly my dear colleague Allan Acosta also had that title, prior to me, and that meant a lot to me.

ZIERLER: Oh, of course, given who Acosta was to you. One award that's sort of on the outside, beyond your scholarly expertise, the John Wesley Powell Award for American Canyoneering—first of all, tell me, who was John Wesley Powell? What did he represent for canyoneering?

BRENNEN: John Wesley Powell, of course, was this extraordinary one-armed adventurer, who lost his arm in the Civil War. He was the first to ride in a boat down the length of the Grand Canyon some 250 miles. He had other companions with him but he was a remarkable individual who was the first to find out what was in the bottom of the Grand Canyon. Of course many, many years later, I made the same trip myself through the entire length of the Grand Canyon, something that I did in much greater comfort than he had in his wooden boats. I sailed down in a great, big, rubber raft the whole way down the Canyon. What I did most appreciate about that award from the American Canyoneering Association was the recognition, I think, of my contributions to that sport, of initiating the canyoneering activities in the San Gabriel Mountains and elsewhere in the Southwest. There were a lot of my friends, of course, who recognized that award, too, and it's always fun to celebrate with them.

ZIERLER: What was that trip like down the Grand Canyon, at the bottom? How long did it take and what do you remember of it?

BRENNEN: That was an eight-day trip. We camped each night on the sand banks on the side of the river—in the open air. That was a lot of fun. There was a large group. I think it was about 25 people in the group who sailed down the Grand Canyon with me. It was a lot of fun. It was hair-raising in places, especially the bigger rapids, the Lava Falls Rapids right near the end of the trip through the Canyon. The waves there were humungous, and you thought for a moment that you were—it was hard to know how you were going to survive. I had had previous experience with very wild rivers and going down them in boats, and I had been thrown out on a number of occasions and had to swim—seemed to me—swim for my life, as it were, having been thrown out of the boat, once in Southern California down the Kern River. I actually have photographs of me in the boat just before I got thrown in the air, got tossed overboard, and just after. The same is true of my exploits on the Pacuare River in Costa Rica, where I also got tossed out. That was probably quite dangerous. I got tossed out in a big rapid in the Pacuare River. Fortunately I hung on to a rope that was hanging down from the boat, and my friends in this little boat hauled me back on board before I got into really serious trouble. So, I had had my adventures.

The Grand Canyon was gentler than that, because we went down in a big boat, a big, rubber raft. A lot of fun. I had read, of course, of John Wesley Powell's account of his descent in the years prior to these adventures and admired him for his courage and adventure. I think it's in my blood this desire to see places that are difficult to get to, where you—and it's kind of the same as in research. I was always drawn to places that people hadn't been before, whether those were intellectual ideas, as in research, or in the physical world. That's what drew me to canyoneering—the thought of standing in a canyon in the San Gabriel Mountains, in a place where no one had ever stood before. Pasadena was only maybe six miles away. That's an extraordinary feeling, to be somewhere where no one had ever been before.

ZIERLER: Is that the essence of canyoneering, the art of exploration? Is that what it's all about?

BRENNEN: Oh, yes, for me it was, always was. The actual ropes and so on were devices, skills you had to learn in order to get into these places that were so exciting, turning the corner in the canyon to see what comes next. I remember Garrett Reisman, who was one of my graduate students who went on to become an astronaut—I remember when he and I first descended Eaton Canyon, right above Pasadena. We didn't actually know what we were going to face. We had tried to find out what was in Eaton Canyon before we descended it. I have reason to believe that there, someone had gone before, many, many years ago, that miners had managed to get in there. But I remember we came to the top of this one drop down a narrow galley with a waterfall in it. It looked like a 100-foot drop but it wasn't. It turned out to be only about a 60-foot drop. But it was quite awesome to get to the top of that thing. "My goodness, I am not really prepared to get down this." But yet, with thinking it out, figuring out how we were going to do it, getting down safely—in that instance I ended up behind the waterfall standing on a rock shelf behind the waterfall. All enormously exciting, and fun to do, and fun to do with someone like Garrett who had a similar adventurous spirit.

ZIERLER: Back to the scholarship, in 2005 you published Fundamentals of Multiphase Flow, again with Cambridge University Press. What was the origins for a book idea? What was needed in the field of multiphase flow for a book?

BRENNEN: In that instance, it's fairly simple. There are components of both of my cavitation book that are in there. I think what I felt then was that there were books on all the special manifestations of multiphase flow. There were books on granular flow. There were books on mist flow. There were books on bubbly flow. There were books on sand flow. There didn't seem to be a book that really tried to unify these topics by creating a set of approaches that were common to all of them. That was my idea, to try to set up a basis for all of these flows involving particles, bubbles, drops, whatever, and then display the specifics of each of the kinds of flow in the later chapters of the book. That was my motive. I think that has been fairly successful, that book.

ZIERLER: What is the overlap with cavitation and multiphase flow? Where are they separate disciplines and where is the connecting point?

BRENNEN: Cavitation is one particular type of multiphase flow. There's no separation there. That's why parts of my cavitation book had to be embedded in the multiphase flow book as one specific application of this more overarching approach to flows with individual particles, bubbles, or drops.

ZIERLER: This is to say the multiphase flow must have been broader in its purview.

BRENNEN: Yes, that's what I meant to say.

ZIERLER: When did you start thinking about retiring, about going emeritus? Was that a gradual process for you? Was your wife's illness a part of the thinking?

BRENNEN: Of course it was. I thought about it in the immediate aftermath. I just about gave up on life at some point. I think the reason I was saved was in part due to my daughters. I couldn't inflict on my daughters more pain that had already been caused by the death of their brother and the death of their mother. So, I gritted my teeth and realized I had to somehow reconstruct myself, emotionally, in order to take care of my daughters. Then, very shortly thereafter, I got to know this woman that I had known as a child in kindergarten, and she continued that process of reconstructing my life.

ZIERLER: It saved you, in some ways.

BRENNEN: Oh, yes, certainly, it saved my life. I won't deny I thought about suicide during the tougher times then. But I couldn't inflict that on the people I loved.

ZIERLER: When you went emeritus, did you think about relocating from Pasadena? Did you want to stay nearby for a certain period?

BRENNEN: I loved Pasadena. I loved the Institute. I loved being able to go down to the Athenaeum for lunch. I loved the friends I had at Caltech. I would still be there. But I also had to be aware of the desires of my second wife, Barbara. We commuted back and forth between Connecticut and Pasadena for some years before I finally decided I had gotten tired of that commuting back and forth, and I would move to Connecticut. I moved to Connecticut, stayed there about a year. I didn't like the winter there one bit. Then we came down to South Carolina, to the Charleston area, to visit one of Barbara's daughters, and we liked it a lot, and we decided to buy a house down here. Now, two of Barbara's daughters, whom I regard as my daughters too—they have been incredibly kind to me, all of her four daughters—two of them live locally, one lives just up the state in North Carolina, and the fourth lives in Perth in Western Australia, which has become one of my very favorite places. It is a wild place. When you drive up the coast in Western Australia, you're in the middle of absolutely nowhere. It's just my kind of place! I loved Perth, for that reason. I enjoyed learning of the history of the Western Australians. I took a particular interest in the Aboriginal history, Aboriginal art, of which I still have many examples.

ZIERLER: Tell me about winding down your research group. How do you do it in an elegant way where you know not when to accept new students, you know not to leave anyone in the lurch when you retire, that you graduate everyone at the right time? How do you land all of that?

BRENNEN: That's a very good question. For me, it just dwindled down. I got so tired of begging for money from the various agencies and so on. Money-raising was one thing which I got tired of doing. If you have less money coming in, you take fewer graduate students. For me it wound down kind of naturally.

ZIERLER: How have you remained connected to Caltech, if not physically, being on the other side of the country? How do you retain and remain in contact with your colleagues? What are the kinds of things, of course pre-COVID, that have pulled you back to campus?

BRENNEN: Well, I kept coming back to see my colleagues. That's obvious. The Thomas Building, I retained an office there long after I retired. They were kind enough to allow me an office. I still actually have an office that I can use, but for a number of years I had an office to myself in the renovated Thomas Building. That's something else I was very proud of beginning, the renovation of the Thomas Building. You should go and see that engraved picture of cavitation on the window—

ZIERLER: Oh, I will!

BRENNEN: —of the auditorium there. You asked me how did I remain attached. Then of course going to the Athenaeum and seeing all my old friends again. I really enjoyed the lunches at the roundtables at the Athenaeum. Those were always fun. Over the many years that I was associated with Caltech, I had many, many friends, friends I wouldn't necessarily otherwise have had connection with. People like Ed Lewis, the biologist. Marvelous man. A lovely man, with a great sense of humor. I remember Ed played the flute in the Caltech Orchestra during a number of my performances for the Caltech Dramatic Club, and I would enjoy Ed listening at my jokes, my onstage jokes, in whatever part I was playing, so I focused on just him. But also people like Hans Hornung, and Steve Frautschi. Many of them now are gone, unfortunately.

ZIERLER: In 2011, the Fukushima nuclear disaster in Japan, were you involved at all in studying what went wrong?

BRENNEN: No, I wasn't. I wrote about it in my last book, as well as the other major accidents.

ZIERLER: In 2016, again with Cambridge University Press, you published Thermo-Hydraulics of Nuclear Reactors. What does that mean, thermo-hydraulics?

BRENNEN: It means all the science associated with how the heat is created in the nuclear reactor, how it is transmitted from the core out to the cooling fluid and from there into the turbines that create power. There are many fluid mechanical issues associated with the flow of the coolant, and of course the flows that occur in the event of any kind of accident. My book does deal with both Three Mile Island and then the big Russian accident and then Fukushima and exploring what can go wrong. In an earlier time in my career, I was a consultant to the Nuclear Regulatory Commission, and had studied many of those different kinds of multiphase flow. What would happen in the event of this kind of accident or that kind of accident. That was very important, I think, for the designers to have all of those potential accidents analyzed and hopefully avoided. Though in the case of those three big accidents, they weren't avoided.

ZIERLER: From the perspective of thermo-hydraulics, what were some of the commonalities between Three Mile Island, Chernobyl, and Fukushima, and what made each disaster unique?

BRENNEN: Each of them involved the escape, of course, of hot fluid, hot nuclear reactive fluid, some form or another, and those were commonalities to all of them. There were also great differences. Chernobyl was truly an explosion. That was the most dangerous of all, and of course the area around Chernobyl has been closed for decades, at least. Fukushima was unfortunate. It really was. I don't think anyone had thought about a tsunami infringing on the cooling system of this nuclear reactor and destroying the cooling system such that it heated up. All of these accidents involved the overheating of the core and the release of radioactive liquids and gases from the core.

ZIERLER: As you survey the current state of civilian nuclear energy worldwide, have we learned important lessons? Are you confident that the problems associated with these disasters have been effectively mitigated? Are you concerned that there is a failure of imagination, like with tsunamis in Fukushima, where we might not be sure what the next disaster might hold?

BRENNEN: That's a very good question, and I don't think anyone could claim that we've absolutely eliminated all of the possible accident trees. I do think that the modern trend towards small nuclear reactors may well be a way of limiting the potential disasters that might happen with nuclear reactors. In my book, I talk about the design of some of those very small reactors.

ZIERLER: These reactors, we're talking of course about fission. There's no thermo-hydraulics component for fusion?

BRENNEN: Not to my knowledge, but I'm very doubtful that fusion will ever occur.

ZIERLER: Have you remained active as a consultant at all in your retirement years?

BRENNEN: Just on a minor level, on things that I enjoy and am interested in. There are a number of companies that occasionally call me up. I've cut back on that too, really, because I don't need to do that. If someone came to me with a fairly unique problem, I might be interested in doing it, but I've cut all of that out, too.

ZIERLER: What about keeping up with the literature? What's simply interesting enough for you that you would want to read an article?

BRENNEN: Oh, boy. I'll read something about, for example, small reactors, or read something about novel aircraft designs, or about applications of cavitation. One of my most recent interests was an effort to use cavitation to inject, into living cells, stuff that you wanted to get into living cells. I think that has been successfully accomplished. It's remarkable. When this bubble collapses into a very tiny, intense point of light and force, it has a way of drilling a tiny hole in a cell wall in such a way that that cell wall will heal over after the process has injected something into the cell. Or removed it. I mean, there's tremendous possibilities. That interests me a lot, the use of cavitation and related phenomena to control what's in a cell and how it evolves.

ZIERLER: Is this a new development? In earlier points in your career would you have ever considered the biological component to cavitation or multiphase flow?

BRENNEN: Not to that extent, but I was very interested in using the intense force and heat that a collapsing cavitation bubble can have, and there's a wide variety of applications for that. The biological one I think is the one that is the most interesting and has the most promise, for improving the human condition.

ZIERLER: In your retired life, as the burdens of teaching and research recede, what kinds of hobbies have you picked up? What's fun for you to do, whether it's canyoneering, or perhaps woodworking, writing? What are the kinds of things that occupy your days, these years?

BRENNEN: All those three things you mentioned are certainly ways that I pass my time. I enjoy writing. I particularly enjoy writing up my adventures in canyons and other places around the world. I enjoy some woodwork. I enjoy the garden to the extent that I'm able to do it, with my current knees. I have lots of little interests that certainly pass my time. You can see the shelves behind me still have lots of books, though I must have given away 100 times more books in my life than you see in the shelves behind me. Only a very special book gets to stay in those shelves for very long. Usually they're somewhat esoteric.

ZIERLER: Of course I'm sure you still get to visit with your daughters and your new kids, from Barbara.

BRENNEN: Right, new kids. Barbara and I have a combined family of six daughters, each of whom is a great delight to me, each of whom contributes enormously to our life. And now we have 14, 15 grandchildren.

ZIERLER: Oh my goodness.

BRENNEN: And we have two great grandchildren—

ZIERLER: Oh, wow!

BRENNEN: —in Perth, in Western Australia. I know that Barbara is intent on getting to see these great grandchildren. Whether I can make it all that way to Perth now with my knees, I'm not sure.

ZIERLER: Well, look, between hiking your next canyon and getting to Australia, that's reason enough to get your knees fixed up.

BRENNEN: Yeah, I guess so. I guess they're good at that. I'm just apprehensive. Physically I've been very fortunate in that I've maintained my strength, my health, for my almost 82 years now. But my knees have clearly given out and need to be replaced. I hope I can resume some kind of walking or hiking ability after that.

ZIERLER: Chris, now that we've worked right up to the present, if I may, if we can close our wonderful series of discussions together, I'd like to ask a few overall retrospective questions about your life and career, and then we can end looking to the future. What would you say is the lesson, the great lesson, for readers of this transcript, in learning about your life? From Northern Ireland to Oxford to your extraordinary opportunity to come to Caltech, what are the things that you learned along the way that might serve as a guide for other people as they think about how to forge a career in science and engineering? What lessons might you share?

BRENNEN: I want to say something in general, not necessarily about science and engineering—to be kind. Kindness is something that's very important to me. [emotional] People have been very kind to me through all of my trauma. So I think being kind, and being generous, in your time. Contributions to humanity, I think is the most important thing of all. I look back on my time at Caltech—the things I really feel most moved by, were the students whom I managed to help, so that they survived whatever trauma they found themselves in, or whatever difficulties they found themselves in. There were a number of students whose lives I saved in various circumstances. I feel sad about some of them that I wasn't able to save. There weren't many of them, but there were some, and those are deep regrets, when I think back. You always think, "Couldn't I have done more? Couldn't I have done something?" That would have saved that individual. That's what I think of, when I think about all my time at Caltech.

I was privileged to spend my career at Caltech, really enormously privileged. I feel the opportunities I was given by my education, opportunity to get to Caltech and to work at Caltech for 40 years, it was just a delight. The people I worked with were a delight. I tried to give back some of that to the troubled students, to the troubled staff members too, sometimes. That's what I think of. And I think of the people—both of my wives, and my two daughters—who were most involved in maintaining me and allowing me to survive the tragedies that I experienced. I guess that's what I think of. I We talked about these awards and so on, and I'm enormously proud of the Feynman Award, and of the John Wesley Powell Award, but the rest don't mean a whole lot to me, to be honest. I still have them on the wall. If I turned around, you would see a number of plaques here from various teaching awards. But that's what I think of most. I've been very lucky, enormously grateful for the experiences, and for the help in overcoming the tragedies that we talked of.

ZIERLER: It's obvious you've achieved the right balance between working hard and playing hard. What is that balance? When do you know when to stop and enjoy yourself or just take a deep breath? Conversely, how do you use that as a way to recharge in your academic life?

BRENNEN: Very good question. I certainly feel that there were many times I was stuck on a problem or stuck on trying to figure out a piece of an instrument, when I would say, "I can't figure this out at all. I can't think of what to do." I would go out and I would be climbing some rock face somewhere, and suddenly because my mind was empty a thought would just come into my mind. What I might do differently, to solve that academic problem, whether it be an instrument or a piece of mathematics or whatever. They were complementary. I think people who do nothing but work cannot be inventive. I worried about my Japanese friends. There is this culture in Japan of working for ridiculously long hours. I mean, hours that reduce you to a sponge of lack of ambition, lack of incentive. So, I was very glad to have that, and people like Garrett Reisman, Mark Duttweiler, my other students who went on these hiking expeditions with me, they helped me to get into kind of a state in which advising them was something I really wanted to do. Doug Hart, I should have mentioned also, who is now a professor at MIT, he was another of those early companions.

ZIERLER: If you reflect on the major questions in cavitation, hydrodynamics, multiphase flow, if you compare the frontier of knowledge when you first got in this business 30 or 40 years ago compared to what is known now, what has been resolved and what really remains an open question?

BRENNEN: I think in terms of cavitation, some of the major leaps forward came from the development of exciting experiments, clever experiments, and clever instrumentation. One of the people who first photographed the details of a cavitation bubble collapse in particular was Albert Ellis. He was a Caltech associate professor, I think, way back. He devised very high-speed cameras, a million frames a second, that were able to capture these intensely violent, microsecond phenomena. People have now gone on from that to look at it even faster, in tenths and hundredths of microseconds. In order to understand what's going on, you need that kind of instrumentation, and it takes real genius sometimes to find ways to make those observations. To me, at least in the subject of cavitation, the real advances have been the development of that kind of instrumentation. For example, measuring the noise, something I did, as we already discussed, in my early days—you had to measure the noise but without interference from the reverberations in the water tunnel or whatever you were using to create the cavitation. That was hard. It may sound like something simple, but getting pure cavitation noise, that was something. Steve Ceccio, who is now a professor at the University of Michigan, made very significant advances, when he was a graduate student, in measuring the noise.

ZIERLER: For having spent your entire professional career at Caltech, for all of its strengths, all of the unique ways that Caltech does research, what do you think in your career was made possible only because you were at Caltech, and what do you think you would have accomplished no matter what university or institution you were attached to? I wonder if you've ever thought about it. I know it's an impossible question to answer.

BRENNEN: It is really impossible, because you can't really—sometimes I wonder, where do these ideas—for a new instrument, or a new approach to a particular mathematical problem, or a new device—where do those ideas come from? It's usually strands, connections from a whole different set of things you've seen and done that somehow connect up to suggest something new. There's not much new in the world, of research, but there are new connections, new things that come together, to make an advance possible. That's what I would say. I look back, and the people that preceded me at Caltech, people like Albert Ellis and Allan Acosta and Ted Wu, all of whom in their own way came up with some new way of doing things that led to new discoveries.

ZIERLER: As you survey the current faculty in EAS who are carrying this mantle, what are you most proud of in terms of your contributions building a foundation, just like your predecessors in the generation before you provided a foundation for you?

BRENNEN: That's also a good question. I had a role, I think, obviously, in hiring a number of very bright young faculty members in Mechanical Engineering, primarily I'd say Tim Colonius and Melany Hunt, who have both gone on to do some great things in terms of their research, different areas. There are many others, but they are two of the people that I look back on with most pleasure in having helped their careers.

ZIERLER: Finally, if I may, last question, looking to the future. If you survey all of the students whose lives you touched, either as postdocs or graduate students where you were serving in a mentor capacity, or all of the undergraduates that you interacted with as dean of students, as master of student houses, as vice president for Student Affairs—as you look at the ways they have forged their careers, their future, what gives you the most satisfaction in a composite since?

BRENNEN: Well, they've gone in all kinds of different directions. I hope I invested in them the drive to look at something new, to try something new, not to be afraid of failing. I think that's very important. Because if you're afraid to fail, you'll not do any of these things, or you'll do very much reduced objectives. That's what gives me the most pleasure, to see people like my graduate students—and many of the graduate students, of course, who did do canyoneering with me—Doug Hart, Garrett Reisman, Clancy Rowley, Mark Duttweiler, and so on—and they were great companions as well. I enjoyed their companionship as much as I enjoyed their scientific success. They all remain great friends, and I continue communication with all of them, all 33 or 34. I think there are one or two that I have lost track of, but I try to keep track of all of the former graduate students. Unfortunately several of them have died, of course, as is inevitable, and that's sad.

ZIERLER: But what a legacy to have built and to see continued from one generation to the next.

BRENNEN: I hope so, though I don't think of it that way, I must admit. When I'm gone, my legacy, obviously it doesn't mean anything to me, so I'm not sure I think that way. I think about, what can I do next that would be fun? What piece of woodwork can I do? What can I collect? What can I write about? I do enjoy writing a lot and I hope that I write in a decent way. I'll continue to write, just as I do right now, in this position, in this office—

ZIERLER: Wonderful.

BRENNEN: —the rest of my life.

ZIERLER: Chris, this has been an extraordinary series of discussions. I want to thank you so much for sharing all of your perspectives and insight, and for being so honest about just the triumphs of life but also the tragedies. It's very important, and I'm so appreciative that you shared that with me. I'd like to thank you so much.

BRENNEN: My pleasure, and thank you, David, especially for your kindness and your thoughtfulness in terms of the questions. Thank you.