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Marshall Rosenbluth’s Interview

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Marshall Rosenbluth was an American physicist who worked in the theoretical division at Los Alamos from 1950 to 1956. In this interview, Rosenbluth addresses the theoretical issues involved in designing both the atomic and hydrogen bombs. He discusses how the pressure to create a nuclear bomb before the Soviet Union affected work in the laboratory, especially in performing and checking calculations. Rosenbluth also recounts his experiences during the nuclear weapons tests at Los Alamos and Bikini Atoll. He recalls the roles of top scientists, like Edward Teller, Hans Bethe, Enrico Fermi, and Carson Mark, in the building of the hydrogen bomb. He also explains how funding and other external factors affected the hydrogen bomb’s design.

Date of Interview:
May 26, 1994
Location of the Interview:


Richard Rhodes: How did you get involved in the program?

Marshall Rosenbluth: Well, you can probably guess. I’ve already told you that I was a student of [Edward] Teller’s. I was in the Navy during the war and then went back to the University of Chicago where my parents were living, to graduate school, and became a student of Teller’s. I’m not quite sure exactly how. He was a professor in one of my courses.

He was a very permissive thesis advisor in the sense that he sort of never talked to me about it and I could do what I want, and that was fine with me. And then he offered me—he said, “Would you like to come work in Los Alamos in the summers?” So I went a couple of summers to Los Alamos.

Rhodes: Starting when?

Rosenbluth: I think the first is the summer of ’48 and ’49. Then I went off to Stanford. I had an instructorship at Stanford, starting the academic year ‘49/’50. A number of things happened during that year that Teller, of course, kept trying to urge me to come back to Los Alamos. One thing that actually weighed fairly heavily in my decision was the [Klaus] Fuchs business, when they arrested Fuchs.

Rhodes: Because?

Rosenbluth: Well, of course, I knew that they were working on, that we were working on the hydrogen bomb and I thought that would make a qualitative difference. It was clear that Fuchs knew at least about the early work on that, so he would’ve told the Russians that we working on the hydrogen bomb.

Rhodes: And in fact—

Rosenbluth: And he did.

Rhodes: Sure.

Rosenbluth: So, I assumed that they would be working on it and I thought [Joseph] Stalin was just a terrible son-of-a-bitch. If he ever got the bomb before we did, it could be very dangerous. So, that was basically my motivation. Then sort of when Stalin died, I got out of the business.

Rhodes: I understand that [J. Robert] Oppenheimer said something about Fuchs along these lines: If Fuchs told them about the early work on the hydrogen bomb, that’s great, because then they’ll be in the wrong direction.

Rosenbluth: Well, that was a little flip. I mean, it’s true, of course, it was kind of in the wrong direction, but the fact that we were working on it and I’m sure they got started much—in fact, that was another thing that I learned on this drunken—when I was being taking around by this drunken bureaucrat.

I sort of asked him whether, I said, “There was a lot of discussion in the United States in 1950 about whether we should work on the hydrogen bomb. Do you think that had any influence on what you were doing?”

He said, “Of course not. We’re working on it as hard as we could and it didn’t matter what you were doing.”

Of course, that also reads in [Andrei] Sakharov’s book.

Rhodes: Well, even Sakharov, actually, the first document that the Soviets put together on the thermonuclear was in ’46, and I think it was probably directly in response to Fuchs’ information.

Rosenbluth: I think it’s pretty clear that if we had decided not to work on it, it wouldn’t have made any difference as far as their—

Rhodes: They really got seriously going in ’48, which is when Sakharov was hired and so on, yeah.

Rosenbluth: So, anyway, that, I guess, is sort of why I went into it.

Rhodes: Was your thesis work, or your particular specialty related in any way to—

Rosenbluth: No, it was on energy physics.

Rhodes: Close enough.

Rosenbluth: What?

Rhodes: Close enough?

Rosenbluth: Well, not really. So, anyway, as I say, I went there for a couple of summers and then I went back in ’50 and stayed in Los Alamos until ’56 when I then came out here. I guess the first half of the time I was there, I was working mostly on the H-bomb and then the second half I got off into quantum physics and controlled fusion, which is mostly what I’ve been doing since. At that time, that was also a classified program.

Rhodes: The summers that you went, did you have a sense that this was, that the H-bomb was not being pursued as Teller has always felt?

Rosenbluth: No, I think it’s more a matter that, or again, I saw things mostly through the eyes of the theory division, which I was in. But, there were really very few people there. There were maybe, I don’t know, eight or ten people, eight or ten Ph.D.s. And the only one you would really consider a first-class senior, of course, this was Teller himself, at that time. I’m not sure when he came back fulltime, he was working on it. So, if you thought it was an important problem, you could say that the level of effort was pretty low.

Rhodes: Were those people also working on the fission bomb, too?

Rosenbluth: Yeah, they were, so actually only a fairly small part of that effort was H-bomb. But, I mean, for the number of people who were there, I wouldn’t say that certainly nobody was discouraged from working on H-bombs. It was part of the program.

Now, I don’t know what would’ve happened if the government decided they didn’t want to pursue it instead of that they did. But, I guess, I was actually at Stanford during the period when they made that decision. But, before then, people were certainly working on it.

Rhodes: You mean the decision to terminate at the end of ’49?

Rosenbluth: Yeah, right, right. So, that was the year I was at Stanford.

Rhodes: Oh, I see.

Rosenbluth: I don’t know what implications that actually had within the laboratory. Certainly, so the summers that I was working there were before that, and there were certainly a number of people working on it. It was clearly, from a science point of view, more interesting and also seemed potentially more important. I could never get very excited about small changes in the fission bombs.

Rhodes: When you came to Los Alamos full-time, what did you do?

Rosenbluth: Well, I worked essentially on the H-bomb theory.

Rhodes: Meaning, what part of?

Rosenbluth: Well, of course, part of the problem, as I say, is like, it’s forty-five years ago and recall isn’t so great. Part of the problem is that I really don’t know what’s still classified and what’s unclassified.

Rhodes: Well, I mean, the hydrodynamic calculations that seem to have been a very important of all this.

Rosenbluth: Well, there were hydrodynamic calculations, calculations of the properties of matter under these conditions. I guess those were the transport calculations, radiation transport, things like that, were part of the problem. I sort of worked on all of those. I think, of course, I was a junior person and a Ph.D., so I didn’t get consulted and wasn’t involved in any high management level discussions of what should be done or what was going on.

Rhodes: Were you working for Teller?

Rosenbluth: Not directly. I was working, I mean, I was a member of the theory division, which was supervised by Carson [Mark]. And, it was a small enough group that sort of everybody talked to everybody pretty much, including Teller, of course.

Rhodes: Well, let me ask, see if I can ask some specific questions. One of the things that puzzles me is that Teller says and others have said is that radiation implosion was discussed and thought about as early as the Super conference. But nobody could see—

Rosenbluth: Now, what do you, what are you calling the Super conference?

Rhodes: ’46, sorry, the one in April.

Rosenbluth: That was before my time.

Rhodes: Nobody could quite see how to make that work. And Teller, when we talked to him at Los Alamos last summer, talked a great a deal about the problem of energy being lost through various processes and not making it, until the idea of the secondary and the primary—

Rosenbluth: I hope that’s unclassified.

Rhodes: Oh, yeah, very much so, yeah. It just wasn’t clear that you wouldn’t lose as much energy as you were gaining along the way. That was his point.

Rosenbluth: Right.

Rhodes: And, yet, it’s not clear to me why there was that great gap between—if the idea was there in the first place, why it took so long for it to come out and be clear.

Rosenbluth: Well, again, here I’m worried about classification issues. It would be nice if there were some classification guide. So I don’t want to say too much about that. This must be frustrating, but there are obviously different approaches to the problem, geometrical approaches. I have my own philosophy of how the truth emerged out of all this, which is partly, I think, certainly, the person who was really responsible for most of the key insights was Teller, I think now.

Rhodes: Well, what’s been made public is something like this. Stan [Stanislaus] Ulam was working and trying to figure out a way to get a bigger fission bomb. And, realized that he could perhaps have two fission bombs staged using the blast from one to compress the other much more efficiently than simply high explosives could do. He took that idea—he then realized that this might also work for a hydrogen device. Took that idea of a two-stage energy-driven rather than, or a blast-driven, to Teller, who then saw the idea the idea of using the radiation—

Rosenbluth: Yeah, I think that’s right.

Rhodes: —to do the implosion. And, then later worked out the idea of a second spark plug.

Rosenbluth: Teller?

Rhodes: Teller.

Rosenbluth: Yeah, that’s right.

Rhodes: So, that if that’s sort of how it happened, Teller is reluctant to admit even that much these days, I will say.

Rosenbluth: Well, now, you know I couldn’t totally verify that because I knew what Teller was thinking much more than I knew what Ulam was thinking. So, it wouldn’t be totally fair to Ulam—I mean, I never heard this idea from Ulam at the time. On the other hand, that’s no reason to say he didn’t come up with it.

My opinion is Ulam, who was a very bright and charming guy, but not a physicist. He tended to kind of wander around with rather vague ideas. I mean, which, now, I can easily imagine him saying, “Well, we could use one bomb to ignite another,” on that level of vagueness. Whether he would go the next step further and say the blast, it seems very likely, but I never heard it.

On the other hand, Teller, when he came to you, would have thought things out in much more detail. But, Ulam was in the category that 95% of what he said, you could kind of dismiss as useless. Teller, maybe eventually 90% would be useless, but would take much more thought and calculation to realize it. Both very inventive people, but—

Rhodes: And, when they sat down to write this paper that they first wrote, that they wrote together, apparently Ulam did sit down and try to quantify his version versus Teller’s version. I haven’t seen the paper, the paper is classified, but the title is not.

Rosenbluth: Yeah, I’m not sure I’ve actually seen that paper either, to tell you the truth.

Rhodes: But, the two different kinds of transport, apparently they worked out to—

Rosenbluth: Right. Well, my version of what happened is a little different, which is, as you know, the sort of original Super approach was in deep trouble, as you say, the various energy losses and so on. And, this far, I think I’m on firm ground that partly as a result of being frustrated and not quite knowing what to do, rather than doing nothing, the thought was, well, what can we do with thermonuclear reactions, what experiments can we do?

One idea, and I’m not sure who, whether it was Teller’s or who it came from, was the idea of the booster and that actually was the first thing I got involved in—using the booster to release a flood of neutrons and enhance the fission bomb yield.

The second idea was to try to look at some burning thermonuclear fuel, DT, and in order to do it in a way where you could clearly diagnose it. And, it wasn’t sort of very obvious where this was going to get you, other than it was an experiment with the relevant material, which you could look in detail how the temperature was changing, the density was changing, all sorts of neutrons were being produced, and all sorts of detailed diagnostics.

The idea—and again, I’m not sure whose it was, may have been Teller, may have been somebody else—was that, well, how are we going to do this? We want to put this DT where we can see it, not in the middle of an explosion, so we’ll pipe some radiation out to it. And it’s sort of obvious that once you start doing detailed calculations on radiation flowing out from bomb to this little test experiment you’re doing, that your way of thinking, and a lot of people involved in this, may lead you to the thought of why not use a radiation implosion in the secondary and similarly on the booster?

Doing the calculations of how it was going to get imploded and how it would interact with the fissionable material around it was going to be very much related to what you would want to see in the secondary of a thermonuclear explosion.

At least my feeling was that this is kind of a paradigm of the way physics was done; you reach a certain point in your theoretical thinking and then you get stuck for one reason or another and can’t go any further. But you try to think of what experiments might you do that would shed some light on the situation, even if it’s not very obvious how you go from here to there, to actually where you’re trying to go, which in this case was the H-bomb, by these experiments. I can see a very clear path.

I mean doing these booster calculations, I discovered a couple of things which were not great physics, but they were interesting and unexpected. And, I talked to Teller about them and he would be excited, and then a number of things that I think were mostly as a result of the thinking and the planning of these experiments that, at least in my opinion, kind of lead Teller to have this idea of radiation implosion. And these insights, I mean, he came up with the radiation implosion before these experiments ever actually got done.

But they were done in ’51. It was George and Ivy [Mike]—George was the DT shot and Ivy was [inaudible]. They both worked as we calculated essentially and beautiful diagnostic experiments, you could really see details going on, so if nothing else, we had a firm level of confidence that what we knew how to calculate these things. But I think that was really kind of a logical train that lead up to it.

Rhodes: Which wouldn’t necessarily mean that Ulam wandering in with an idea of a secondary and a primary wouldn’t be helpful?

Rosenbluth: No, it could be.

Rhodes: It might put together these various things.

Rosenbluth: Well, as I say, I don’t really know.

Rhodes: Teller acknowledges that—

Rosenbluth: I never heard Ulam—

Rhodes: Ulam walked in the door with this primary/secondary two-stage—

Rosenbluth: This may well have been while I was off at Stanford, for example, was when he really talked about it.

Rhodes: It was April of ’51.

Rosenbluth: ’51? Well, that was when the idea was, or that was when the paper—

Rhodes: It was when the idea occurred, if I got my dates right.

Rosenbluth: Okay. Well, I was there then. I guess I just didn’t hear that.

Rhodes: Well, I guess, I am curious about this because I’d be interested in knowing how this discovery which everyone apparently, as soon as they heard of it, said, “Aha,” how it’s kind of propagated through the laboratory.

Rosenbluth: Well, it wasn’t—

Rhodes: Was it coming [inaudible]?

Rosenbluth: Well, the radiation implosion?

Rhodes: Uh-huh.

Rosenbluth: Well, yeah, I talked frequently to Teller and I think after he’d had this idea, we talked about it. And, I’m not sure that it is fair to say that everybody immediately said, “Aha.” Everybody realized that this was a new way of looking at the problem and of course a number of questions immediately arose and people did calculations.

I admit, after a couple of months the calculations looked pretty good, but they were still pretty crude, and it was probably another, oh, I don’t know, year before really detailed calculations had been done. Meanwhile, we had the experimental results from Greenhouse [Test], which gave us some confidence in the calculations and we were using some of the new computers to really do detailed calculations. I think by the time that Mike was actually shot, there was a pretty high degree of confidence that it was going to work.

Rhodes: Maybe with a higher yield than it had. Bill [William George] Van Dorn, the—

Rosenbluth: I’m trying to remember what—

Rhodes: The oceanographer down the road says Teller came in and said, “We may need to deal with tsunamis here, or we may be talking 100 megatons.”

Rosenbluth: I don’t, I don’t—

Rhodes: I find it hard to believe.

Rosenbluth: You know, I don’t even remember the details. I don’t think there was even enough material to do that.

Rhodes: I’ve been warned about Bill Van Dorn. He’s an oceanographer, not a physicist.

Rosenbluth: Right, right. Well, he told you he’d like to see a tsunami.

Rhodes: I know, exactly.

Rosenbluth: Well, of course, I suppose there was always, could’ve been some residual uncertainty about, well, even for a given yield of that magnitude, what it might, how it might couple with the oceans.

Rhodes: Oh, yeah.

Rosenbluth: I’m sure people’s calculations wouldn’t predict any tsunami, but it had never been tried before. You know, there were scares about igniting the atmosphere.

Rhodes: Yes, right. Teller was very much involved in working on all through.

Rosenbluth: That was something, I guess, it sort of kept cropping up and people would show up at the lab and suddenly start worrying about this. And I guess we did have a period where we all sort of rushed through and redid it independently just to make sure we came up with the same answers we had during the war.

Rhodes: The fact that radiation could exert that kind of pressure was known as far back as the Los Alamos Primer, right? It seems to me there’s a diagram—

Rosenbluth: Well, depends what you mean by—I mean, the basic physics that you could transport energy by radiation and then you could’ve given a suitably sanitized version to a graduate student in the physics department in those days. And, he would’ve kind of tell you that that would happen, that radiation would get absorbed and you would blow off the material and you get a rocket pressure during implosion. So, that wasn’t a new discovery in physics.

On the other hand, the sort of details of just how much it would penetrate and the interaction between the hydrodynamics and the radiation, that was something which I don’t think had been worked out before anywhere. That was one of the things they did when I was there. So, the quantitative details were new, and new theories and using new computers. But the basic physics was really not new, and of course. The basic invention was new. After you do it experimentally, clearly was no—

Rhodes: Were you involved at all in the Alarm Clock?

Rosenbluth: Not very heavily. I mean, I did do some on that.

Rhodes: Because, the first—you probably know this—the first Soviet bomb test, they call it a layer cake.

Rosenbluth: Right.

Rhodes: I’ve been corresponding with one of the men who designed that, Yuri Smirnov, Sakharov, Smirnov and a couple other guys worked on that design. It was primarily Sakharov’s, I guess. And, they were all very concerned to argue that that was justifiably called a hydrogen bomb. They pointed out that it had a fusion yield of 15 to 20%, which was comparable to many of our bombs. That much we do know. And, that they could have run it up to as much as one megaton. In fact, I think they tested a megaton, a later design.

And, that they did test one without any tritium, with lithium, later on also. This doesn’t satisfy Herb [Herbert Frank] York at all when I tell him these things. That the Russians are very concerned to argue that this thing was a working bomb, that really was a major fusion explosion.

Rosenbluth: Well, he had what, a 200-kiloton yield.

Rhodes: They say 400. What size it was, these things I don’t know. A bigger would have been if they’d gone up to a megaton.

Rosenbluth: Yeah, I think we figured pretty much, shortly after collecting the debris that that’s what it must have been.

Rhodes: Well, we talked to George Cowan when we were down at Los Alamos, and George is very skeptical. He says, “Ah, they’ve put a bunch of tritium in the core and—

Rosenbluth: Well, that’s right. What we didn’t know was how much tritium—

Rhodes: And it did have tritium, but Smirnov says it was a design that would’ve worked without tritium. 

Rosenbluth: I’m not really sure why, I mean, we had the Alarm Clock, of course, sitting around with the possibility long before the radiation implosion.

Rhodes: Yeah, ‘46, ’47, ’48.

Rosenbluth: I’m not quite sure why somehow people never seemed to get very enthusiastic about it.

Rhodes: Well, I think it was because it was so big.

Rosenbluth: So big.

Rhodes: Physically so big.

Rosenbluth: Physically big and the sure designs used a lot of tritium.

Rhodes: And, it was a dead end, you couldn’t get a very big, you couldn’t go—

Rosenbluth: Yeah, I mean it didn’t look like it was the thing to go to megatons with.

Rhodes: They, on the other hand, how we know there were two of them at that point [inaudible] ’50, ’51 when they were working on that.

Rosenbluth: I don’t know when they came up with the radiation implosion work.

Rhodes: ’54.

Rosenbluth: ’50, that’s when they thought of it?

Rhodes: Yes, and they say and then Sakharov said that they didn’t measure the fallout from our shots, that would’ve given the information that they did not. They didn’t have the sampling system up that would’ve enabled them to do that and they didn’t have the equipment to measure that subtle of a—

Rosenbluth: Well, apparently not. I guess as far as we can tell, they had very little information from our program after Fuchs left.

Rhodes: Yeah. I don’t know of any that they’ve acknowledged, that came, although, Fuchs did tell the American FBI man that he had been asked by the Soviets in ’47 about the tritium bomb. He said it startled him, he hadn’t heard that phrase before. But, that doesn’t ring true, because he was at the Super conference. He knew everything that was known at Los Alamos in ’46 about it, and tritium was certainly part of the conversation.

Rosenbluth: Right.

Rhodes: So, I think that some of what he passed, or what he told after his confession was designed to obscure his continuing activities until the late ‘40s. It does look as if he was passing information after Harry Gold, after his last contact with Harry Gold in September of ’45, that he may have been Perseus. You know that. But anyway.

Rosenbluth: Well, I don’t know how much—did he really have any access to the U.S. bomb program after he went back to England?

Rhodes: No.

Rosenbluth: Probably not.

Rhodes: No. Whatever he knew, he knew as of June 15, 1946, but it appears that just before he left, he went over to the library and checked out every paper there was.

Rosenbluth: Oh, really.

Rhodes: I just came across that today. It’s in congressional testimony. So, he was very thorough about making sure he knew whatever there was to know.

Rosenbluth: Okay. Well, I don’t know, I’m not sure what other directions you’d be interested in at this point.

Rhodes: It’s always tricky. It’s hard to know what to ask you to elicit those memories of yours.

Rosenbluth: Oh, right.

Rhodes: Were you at the Mike shot?

Rosenbluth: No.

Rhodes: No. You were at the lab at the time.

Rosenbluth: I was at the lab at the time.

Rhodes: Can you characterize what was going on in that?

Rosenbluth: Yeah, it actually the immediate situation was rather interesting. We were all sitting in the lab director’s office. The lab director, I think, was himself off at the shot. But maybe ten or fifteen of us, were sitting there in his office because his office had some sort of communications hookup with the command center in the fleet. And, you know, we waited. I guess we received a notice a few minutes before the time, or a couple of hours before the time, whatever, that it was all scheduled and going. And, then we heard absolutely nothing. And, then the hour passed and another hour or two went by, and finally, we got a notification that a blackout had been imposed, even, this, of course, was all secure and classified communication. But, that no word was going to be passed back.

No word came to Los Alamos, except we did get a telegram from Teller, who was sitting out in Berkeley by the seismograph, whatever, “It’s a bouncing baby boy,” or something. But that was some hours later and we were naturally wondering what had happened, or whether there had been some, either a terrible flop or terrible catastrophe like a tsunami or something.

I was proposing the lab should split up into two parts, one of which assumed the test had been a great success and the other was it was a total failure, and people were making jokes like that. And, then we got the Teller message and assumed that it was correct and it was a success.

Rhodes: Was there great enthusiasm at that point?

Rosenbluth: Well, I mean, I’m sure there was. I don’t really remember. I don’t have any recollection of any orgies or anything. But, as I say, I think the confidence level was pretty high. Of course, you’re never sure until it’s tried.

Rhodes: What kind of expectations did you all have? I understood that the yield was considerably larger than people thought it would be.

Rosenbluth: That it was considerably larger on the next, on the 154, the Bravo [shot], yeah. There it was much higher. I have to admit my recollection—my recollection of the Mike shot was that it was pretty much what we expected. I think the first numbers we got were a bit high; the diagnostics were a big high, not terrible off. They may have been somewhat higher than we expected, but I don’t think there was a great surprise of yield. I mean, if anything, the usual surprise that even though you think you calculated something right, that it really came out that way, naturally. So, in that sense it was a surprise.

There was, naturally, the inevitable soul-searching about what we all, I guess, would have liked it in a way if it had flopped, and it had flopped not just because we were being stupid, but because of inherent physics that it wouldn’t work. So, when it succeeded, naturally, one thought more about these issues. What did we do?

Rhodes: Did you then continue to work on these things for a while?

Rosenbluth: Well, for a while. As I said, Stalin died about six months after that.

Rhodes: Yeah, June of ’53.

Rosenbluth: I think March.

Rhodes: Sorry, yeah.

Rosenbluth: So, actually, sort of shortly after that, it looked to me as if the, well, a number of things happened. First of all, it looked to me as if the new people in Russia were these, not nearly as efficient or were, as you probably remember, their initial reaction was to try to maybe remove some of the repression and, of course, that didn’t quite work out and it came back.

Then when [Nikita] Khrushchev came in, of course, there was a definite—partly it seemed to me that the fear that they were controlled by somebody who was really sort of crazy, who might do us in, that fear partly went away. I think I kind of felt from then on that our best course was to do the best we could to try to get into disarmament and get rid of these weapons, which I didn’t think that with Stalin there was any chance of reaching an agreement we could trust.

Also, I thought that maybe, maybe wrongly, but it seemed to me that the qualitatively, we made the H-bomb and even thought the Mike bomb wasn’t deliverable, we already had designed the Bravo, which essentially was. I couldn’t see that it was going really make a qualitative difference to improving it or in theory you could do a lot to make it smaller. And it was already at a level where the bombers at least could carry it. I guess I wasn’t thinking about the Polaris submarines and the like. But it didn’t seem to me that one was going to be really getting any qualitative change in the deterrent level by further improvement.

So, as I said, I thought now probably is the time to switch to try and be friendly with the Russians, and I think we were at least getting along with them. I think that we probably missed some opportunities then. I don’t know. It’s not that I think Eisenhower was a warmonger or anything, but I think he probably could’ve taken more decisive initiatives to try to reign in the arms race.

Rhodes: Well he did, but then the U-2—

Rosenbluth: That’s right, the U-2 did at the end.

Rhodes: It may really have been a chance at that—

Rosenbluth: Of course, the Korean War was still on, which complicated things. I guess his first priority was to get that over with, which I guess was another indication to me of the sort of watershed after Stalin died. I’ll say it again and I don’t think it’s a coincidence that it was only a few months after Stalin died that we finally were able to get that war settled. So, more rational people were in control.

Rhodes: They had their own problems.

Rosenbluth: They had their own, yeah.

Rhodes: Their own struggles.

One of the strange stories that comes out of that era is that [Lavrentiy] Beria was, the only one besides Stalin who knew they were working on their, the Joe 4. When he was arrested and executed, the scientists out at Arzamas thought, “Who do we to in the government to get approval to test this thing?” It was a great shock to [Georgy] Malenkov that there was a hydrogen bomb sitting over—

Rosenbluth: I see.

Rhodes: It came out of Beria’s trial, who was the person a lot said had this secret weapon that he was developing to use against his own country, but in any case.

Rosenbluth: Well, I would’ve thought that when we tested our hydrogen bomb, I think they would’ve been pretty high on the agenda of the leadership there.

Rhodes: Yeah, you would think so, right. It may well be that that’s what got them moving, because I think they put together Joe 4 in a very short time.

Rosenbluth: Well, they were probably working on it, but I would’ve thought that the leadership would’ve, you know, become well aware of hydrogen bombs when we shot ours off.

Rhodes: You said that Bravo was already designed, and the idea of using the lithium—

Rosenbluth: Well, lithium and at least enough calculations to make sure, to be pretty sure it would work.

Rhodes: So, the—

Rosenbluth: Now, Bravo, we did make a mistake where we underestimated the yield.

Rhodes: How did that happen?

Rosenbluth: Nobody thought of it. It was another bit of physics which—

Rhodes: Nobody thought the reaction would be more efficient because of the lithium?

Rosenbluth: Oh, no, it was a detail, which, again, I’m not sure about classification. But, one aspect of lithium interaction, nobody thought of so in fact the yield was about twice what we were expecting.

Rhodes: It must have turned out to be a useful surprise?

Rosenbluth: Well, useful. Of course, I got ten rad of radiation, which I think was probably more due to the wind shift than it was of the higher yield.

Rhodes: But, I mean, in terms of bomb design.

Rosenbluth: Yeah, yeah. So that was sort of my last involvement. I really wasn’t working on bombs anymore, but I took the junket out to see the test.

Rhodes: Oh, you went into the Bravo test.

Rosenbluth: The Bravo test.

Rhodes: Where were you physically located when that happened?

Rosenbluth: Well, I was on the ship that was, I’ve forgotten, what, thirty or forty miles away. And, we had this horrible white stuff raining out on us. I say I got ten rad of radiation.

Rhodes: Wow. This was because of the wind shift?

Rosenbluth: I think the wind shift, probably the wind shift, made the higher yield, maybe, but it certainly increased the amount of radioactivity that came with it.

Rhodes: Is that the first explosion you’d seen?

Rosenbluth: I think I had seen small ones in Nevada. I know I did, I’m trying to remember I think must have been earlier.

Rhodes: Did you have a sense of a real difference of scale?

Rosenbluth: Oh, yeah, I mean it was pretty frightening thing. The thing that immediately came to my mind, and I’m sure must have come to other people’s, must have used the simile, too, though I’m not sure I’ve seen it, and that is you could see this huge thing, fireball and of course, there’s these turbulent rows going in and out, the thing was glowing. It looked to me like a diseased brain, the thing with all the knobs and it looked to me like a great diseased brain up in the sky. And, it did, did spread to look like the edge of it was almost directly overhead, but that probably was partly an optical illusion, but partly because the yield was much bigger than expected. It was pretty scary. It was a much more awesome sight than a puny little atomic bomb.

Rhodes: When I said I was thinking everyone, who ever left any testimony of Hiroshima always said, “I was sure they’d exploded something right over my head.”

Rosenbluth: Yeah, and I’m sure that—

Rhodes: That same sense of, especially there because you didn’t know why.

Rosenbluth: Right.

Rhodes: Just assumed somebody dropped a bomb on their house.

Rosenbluth: So, anyway, it was certainly a pretty sobering and shattering experience. Of course, that was the test, I guess, the Japanese fishermen, because of the wind shift, were also irradiated.

Rhodes: You may have heard that the Bikinians are now offering scuba dives of the Bravo crater.

Rosenbluth: Yeah, I guess they’re talking about it.

Rhodes: They’re talking, well, actually, I know some people who’ve done it.

Rosenbluth: Oh, really. Are the Bikinians actually back in Bikini now?

Rhodes: Yeah. Jonathan Weisgall was their attorney for twenty years. He just published a book called Operation Crossroads that also tells that history. But, they’re back and people are turning the place into a theme park.

Rosenbluth: I was going to say, well, I was going to joke that maybe it’s a variant. Instead of having a casino, you can scuba dive and take your chances on hitting a radioactive jackpot. I guess it’s probably pretty safe by now.

So, let’s see, what else can I tell you? Well, I mean, to repeat what probably I said at the beginning, at least from my point of view, [Edward] Teller was the driving political force and also the driving scientific force.

Rhodes: What, if at all, do you think from your own experience is his argument that if we’d worked harder sooner we would have had the hydrogen bomb sooner? You know, [Hans] Bethe’s contrasted that in that history bit he wrote back in the early ‘50s, was it was an accident. And, Teller said, “Well, who considers it an accident, especially if you’re not the inventor?”

Rosenbluth: Well, as I told you, my theory that the ideas really evolved because we were working towards experiments, you know, even if you didn’t quite know—which, really with those experiments we designed, we didn’t have any idea of radiation implosion. But nonetheless just working on them, working out the physics, having the idea of just pumping the radiation out to the little DT pellet, just because we wanted to get it isolated. If we’d had a strong support with the H-bomb’s goal, I don’t see why that wouldn’t have evolved earlier. I suspect the, since I think the insights flowed from that, I think they would have come earlier, too.

Rhodes: Didn’t you need a smaller primary? That’s another argument that, you probably know, has been used against the notion that it could have been done sooner, that the fission bomb itself needed to be evolved a bit.

Rosenbluth: Well, I’m not—

Rhodes: Of course, in a way, that was neglected too, because it really was.

Rosenbluth: Yeah, yeah.

Rhodes: They didn’t test a composite core levitated bomb until ’48. The designs, the early experiments were right at the end of the war, and for two years we sat around with almost no bombs at Los Alamos, because they were saving the uranium to put in composite cores.

Rosenbluth: Yeah. Well, I’m not sure. I don’t think so. I mean, plutonium bombs were quite good for this, but—

Rhodes: There was enough yield.

Rosenbluth: Yeah.

Rhodes: Because, Bethe said something to us about there was a lot of stuff in the way you had to get out of the way.

Rosenbluth: That’s true.

Rhodes: I guess he wanted me to talk to—

Rosenbluth: My memory is not so great on that. But, I don’t recall that, at least by the time I got to work on it, there was, that was never regarded as any particular obstacle or any great feat to design an appropriate primary.

Rhodes: So, it didn’t have to be soccer ball sized in order to, yeah. Well, I have to say when one reads the chronicle of how things happened and when they happened, Teller’s case makes a lot more sense than in the science historian’s version, if you will. They tend to follow the [J. Robert] Oppenheimer perspective on it all.

Rosenbluth: Right.

Rhodes: And, then when you see what the Soviets were doing and when they were doing it, it starts to come in focus, too.

Rosenbluth: Yes. Well, I’m sure the Soviets certainly would’ve gone right ahead, whether we were doing it or not. I guess some people like Herb York crying that it wouldn’t really have mattered if they’d had it a couple of years ahead of time, they didn’t have a delivery system, we could’ve caught up—I think that’s kind of hindsight because at that time we didn’t know how easy or hard it was going to be to do.

Rhodes: Well, probably also neglects the political consequences, too, which is certainly what the record is full of in Washington. People just terrified that the Soviets would test a hydrogen bomb before we did. I find that a little hard to understand at this distance, because there would’ve been one bomb. It’s sort of like saying North Korea has one. So?

Rosenbluth: Well, that may make a difference, too.

Rhodes: Yeah.

Rosenbluth: But, I think more than that, at least the way I would look at it is that at that time it looked like an awfully difficult thing. Now, you know, this might take decades, and on hindsight of course, it didn’t turn out that way, but I don’t think that was really predictable. So, it seemed to me that if you decided to let the Russians go ahead and do it while we weren’t, they might, you know, have many bombs or even stockpile them while we do it.

Rhodes: Why did it look so difficult? What was difficult about it?

Rosenbluth: Well, we were off sort of on the wrong track, as you say, and the problems of the particular geometries and what-have-you that we were looking at just didn’t work out. And, we had to really go to radiation implosions and so on to—

Rhodes: And, it wasn’t’ obvious that there was another alternative, or other alternatives?

Rosenbluth: No, I mean, it took an invention, and it certainly wasn’t obvious that that existed. I mean people were, as you’ve no doubt read, pretty pessimistic in ’49, ’50, here. I guess one thing Teller always provided, probably in his later career, not very successfully, was sort of this optimism that you would find a way to make things work out, even if he didn’t quite see how, which in the H-bomb case was true.

Rhodes: Is that simply a characteristic of his? Is that something you’ve encountered in a similar form in other people?

Rosenbluth: Yeah. Well, certainly, some people are like that.

Rhodes: Was [Enrico] Fermi like that?

Rosenbluth: Fermi was much more, certainly, unemotional and just sort of going like a buzz saw toward the objective. But no, I wouldn’t associate him with anything as irrational as optimism or pessimism.

Rhodes: Yeah, right, exactly. When Teller invited you to come to work on this project, was it in any sense messianic? Was it a casual invitation?

Rosenbluth: Well, I think he was trying to recruit people, certainly.

Rhodes: Because, he seems to have been very personally upset by the Soviet Joe-1 test.

Rosenbluth: Well, that’s true. I guess the Joe-1 test was this year when I was at Stanford.

Rhodes: ’49.

Rosenbluth: So, that probably also played some role, I think, but it was more of the [Klaus] Fuchs revelations. Because, I was sure that meant that they were working on H-bombs.

Rhodes: Oh, okay, yeah.

Rosenbluth: Because, Fuchs was there when at least the early thinking had been done. So, I was sure this meant they were working on it, and it was a worry. I supposed Teller was always pretty messianic.

Rhodes: Yeah, I presume he’s always been the forceful presence that he still is.

Rosenbluth: Oh, yeah. Well, of course, even much more so when he was younger. When did you talk with him?

Unidentified Female: Last summer.

Rhodes: Last summer, yeah, at the 50th anniversary of Los Alamos.

Rosenbluth: I was there, too, but it was probably a different time.

Unidentified Female: Earlier for the—

Rhodes: No, this was the reunion.

Rosenbluth: Yeah well that sort of went on and on.

Rhodes: Oh, okay.

Rosenbluth: They had a couple of days actually on the H-bomb and Teller was there and I was there and then four or five other people.

Rhodes: Oh, that was that earlier?

Unidentified Female: That was classified.

Rosenbluth: That was a classified.

Rhodes: Yeah.

Unidentified Female: Classified conference that was called a couple of weeks prior.

Rhodes: Yeah, right.

Rosenbluth: Well, I say, the person who I think they had the best perspective on this all, who I have enormous respect for, is Carson Mark, because he saw both sides. He probably was somewhat, I would guess, friendlier with [Stanislaus] Ulam than he was with Teller. Later on, he had kind of a falling out with Edward. I never understood why Teller wanted to form the second laboratory, which he, of course, tried very hard to get me to go to. But, that was about the time I was deciding to get out of the bomb business anyway.

Rhodes: It isn’t clear in the record what rational reason he had for a second lab.

Rosenbluth: No.

Rhodes: I could think of other reasons why he might have wanted to get away from Los Alamos.

Rosenbluth: Well, I think it’s undoubtedly true that having the second lab, which has had many, very inventive and creative people accelerated bomb progress. As I say, at that point I couldn’t really see why it was necessary to accelerate bomb progress.

Rhodes: Carson, I understand, is very even-handed about this discussion with him and Teller.

Rosenbluth: Yes. Well, he would’ve clearly been in a position that everybody involved would’ve talked to him and so he would know. It was, you know, sort of his responsibility to put all the ideas together and as far as official lab policy is concerned. And, he was a really wonderful person in dealing with the other people. I’m not sure he really did terribly much technically himself, but he was well aware of what everybody else was doing and how they intermeshed with each other and, you know, suggest, “Well, why don’t you, when you’re doing this, why don’t you go talk to Conrad Longmire, who is doing that.” He was very effective, I think, in getting work out of the group. And, certainly, to the extreme—probably, the best boss I’ve ever worked for.

Rhodes: Well, we’ll see him next week. It’ll be interesting to find out more.

Teller somewhere along the way made a comment about Mike. I think it was Mike, rather than Bravo. He said, “The yield was so high, because we put in everything we could think of, because I was afraid if it didn’t work, they wouldn’t fund the whole thing.” And, I’m curious about putting everything we could think of that we would work.

Rosenbluth: Well I mean there was some truth in that it was over-designed. For example, the outer case which held the whole thing together and held the radiation in, we made five times as thick as the laws of physics could possibly have required because since it wasn’t supposed to be a droppable thing, it didn’t really cost anything. It maybe cost some money, but you didn’t want to leave even a very small chance that something you hadn’t thought of would go wrong.

And, there were lots of things of that type, like more expensive fissionable material in the spark plug and over-engineering of a lot of things that we put in just for safety. And, much more elaborate diagnostics—maybe duplicate and then triplicate of diagnostics, things like that, which I assume you talked to Cowan about. So, in that sense, it was very over-designed and must more expensive than it would’ve had to have been.

Rhodes: As it turned out then they made some deliverable versions of Mike, right?

Rosenbluth: Yeah.

Rhodes: And used that casing which was 30 tons. It’s a huge, heavy thing, right.

Rosenbluth: Well, I didn’t know they’d ever actually made some—

Rhodes: I think the shot was called Jughead or something like that.

Rosenbluth: Reasonable name.

Rhodes: There were a few in between before the lithium bomb came along.

Rosenbluth: Well, I don’t know.

Rhodes: There were some deliverable Mikes made.

Rosenbluth: But not shot.

Rhodes: No, no.

Rosenbluth: Because I think Bravo [was the only one test]. I knew they were all designed. I didn’t know whether they were actually made or not. I knew they were weaponized.

Rhodes: Weaponized, yeah.

Rosenbluth: But, I didn’t know whether they were actually made.

Rhodes: I think a few were actually delivered to the Air Force. Isn’t that that huge Mark 17, whatever it was called, that you see in the museums. It looks like a railroad tank car. Well, Herb was telling me the other day that Mike could’ve been delivered, if you take—

Rosenbluth: Yeah, you could have. It could’ve been pared down.

Copyright 1994 Richard Rhodes. This transcript may not be quoted, reproduced, or redistributed in whole or in part by any means except with the written permission of Richard Rhodes. Exclusive rights granted to Atomic Heritage Foundation.