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In footnotes or endnotes please cite AIP interviews like this:
Interview of Charles Frank by Mark Walker on 1985 April 12,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Origins of British scientific intelligence during World War II (headed by R. V. Jones, with Frank as deputy). Intelligence on nuclear research in Germany; relations with U.S. intelligence (Samuel Goudsmit); comments on Fritz Houtermanns and Carl Weizsäcker. German uranium project and Werner Heisenberg's Farm Hall estimate of nuclear explosive critical mass; postwar German version of their war work; Heisenberg's role in German nuclear research.
... we both went the academic route, when the war was over. He [R.V. Jones] before me, he got a chair at Aberdeen. But for quite a number of years after that, Jones was giving lectures at the Staff College periodically, which gave him, by the British rules, the right to feel himself justified in retaining copies of our war-time reports, retained reports of ADI science. The setup was, that at the beginning of the war, say on September 3rd, 1939, when the war began as far as England was concerned, there was only one intelligence branch for all the services, with a scientist appointed, and that was the Air Ministry, and he hadn't actually arrived to take up his duties. He reported for duty on September 3. So for quite a lot of the war, well, Admiralty Signal's people were good and scientific, so they were, they could look after it, they fully understood radar. So that the Admiralty could look after scientific intelligence, or magnetic mines. So the Admiralty had not explicitly appointed anybody or scientists to intelligence. The War Office did the most extraordinary thing. They decided, when they got to know about radar, mind you they didn't get to know about radar until the war had been going for well over a year, when they got to know about radar they said "that's a kind of search light." Very logical... So they assigned radar intelligence to the man who was in charge of search light intelligence, who happened to be England's cricket captain, a very good chap. But not a scientist. Well, actually that got smoothed over fairly nicely, because he was well aware that he didn't understand a thing about it but it was his duty to write a monthly report about radar development, so he came and appealed to us. The cricket captain of England is rather a good man at getting people to do things, delegate. So I went over to see him and discussed the situation, and undertook that we would write the radar portion of his monthly report on German search lights. And so, it's probably a bit unfortunate, if we hadn't done that, then the War Office would have woken up sooner to the fact that they were short of intelligence on the scientific side. But anyway, Air Ministry was in first, with one man only, for most of the year, and sometimes he was the most articulate of the people who were in the Air Ministry at that time, anyway, the most articulate of the Air Marshals, the man the Air Ministry used to use, when it needed to speak to the nation, the man who talked to the country over radio, the Air Force side of things, so Joubert woke up suddenly in mid-summer to the fact that there was one man, R.V. Jones, one man alone who understood the system of German radio navigational beams, as they were in detail, as they were being used for guiding night-bombers and more important than that, one man, the same man, who knew how we found out what we did know about it. Therefore, one bomb might put out all of our intelligence about such things, Joubert ordered Jones to get himself a deputy without delay, and Jones asked if I would be willing, and so explicitly on November the 5th, 1940, I moved up from Porton where I'd been doing gas masks and smoke-screens to the Air Ministry, and that meant that the number of people in ADI science now rose from one to two. By Christmas it was four. And then gradually it grew. It never got very big. The second point of course is that since he was the only — the second important point by the way — the Foreign Office mistranslated a speech that Hitler made, a speech (German): Hitler said in his speech, "Wir haben eine Waffe, worin wir nicht angegriffen werden können". [We have a weapon, by which we cannot be attacked], something like that, typical Hitlerian grammar, and the Foreign Office somehow managed to make that, translate that to, "We have a secret weapon." And so the newspapers blew it into headlines all over, "What is Germany's secret weapon?" And nobody for quite a while went back to see the original, to see what Hitler really had said, and so, there was a general outcry to find out what was Hitler's secret weapon. The Air Ministry was the only ministry that had a scientist in its intelligence there, and so Jones was asked, was given the run over all the papers of the Secret Service, Jones was given what's not normally granted to people from the intelligence branches, he was especially fed by this secret organization, but he was given the run of the files, so he got his foot nicely in the Secret Service, MI6. So, chiefly by being in earlier than anyone else, the Air Ministry was the only one who had some scientists in its intelligence and the special privilege of entry into the Secret Service and most other things. So that's what ADI science is, Assistant Director of Intelligence (Science), which more or less became the Scientific Advisors to the Secret Service. That's Jones' outfit. I was number 2 in it, and it became very difficult to count who was a member of it and who wasn't, later on, when we had temporarily attached people, like when we — when we knew that some kind of heavy rocket was going to be, there was going to be a continental rocket bombardment, and the result was that the Admiralty then got, Teddy Bullard, geophysicist... well, the Geophysics Labs at Cambridge University, now called the Bullard Laboratories, of course for a quantity of years, their Institute of Geodesy and Geophysics was commanded by Bullard. Teddy Bullard and Francis Crick, you've heard of him, Watson, DNA. So the Admiralty sent over a couple of scientists from their outfit that spent two or three months with us. Now, I don't know whether to say they were members of our staff or not. But there were a large number of marginally attached people there. So I suppose if you made the smallest count, there were about a dozen members of ADI science, if you made the biggest count, there were 30.
Still not very many.
That's it. Right. Now, where do we go from there?
I'm particularly interested in the nuclear research.
Nuclear stuff was not explicitly our problem. But we regarded it as our right and duty to keep a watching brief on anything that... But it was not an explicit general order to all intelligence sources, to send material about that to us. We had sufficiently good contacts with for example the code-breaking people, Frederick Norman, professor of German in London, in peacetime, was supposed to be our liaison man at Bletchley and I guess I talked to Norman on the scrambler phone at least once every day, and anything he thought would interest us, he saw came to us.
But virtually nothing that was explicitly nuclear. One or two things that one wondered what they were, that might be, came from that source, generally turned out not to be.
What we in fact were able to do I think fairly reliably in that class of evidence was, there couldn't in reality be a big German project which had got far enough to be actually thinking of building bombs, OK? Because if they had made it, if it had existed, well, it might not have had to use radio communication lines. If it did have to use radio communication, it would probably have been granted a special color, a special code block, different, so that when you'd broken another line of traffic, you're not into that one, and there were of course lines of German communication traffic which were not regularly read, I think there might be one or two that never were read, but I think there were, from their traffic habit I think we knew that those that we weren't reading, we knew roughly speaking what kind of thing, or really a lot of constraining factors, what kind of thing they might be dealing with.
So I think we were, on the other hand, one could have said of course, if they were making a nuclear bomb, it would be super-secret, and they might have made a ruling that they would never use any radio communication in connection with that, in which case our most reliable source of information would have been unavailable to us. So we were never able to really swear with absolute positive proof that the Germans were not making a bomb. We were only able to say, "It looks to us on all the evidence available that they're not."
The Americans ignored this. Groves certainly did.
I expect Groves did. I never met Groves. I met Sam Goudsmit. I suppose he was my first highly placed person in the outfit that I spent a week with, ever. My thought about Sam Goudsmit, for one thing, I knew that I'd got to be cautious. I mean, I respected Sam Goudsmit, he's a good scientist, and an honest man, but his father and his mother had been picked up in Holland, taken to a concentration camp, and died there. I never thought — I thought, I was never, must never rely on Sam Goudsmit alone for an assessment of the, what shall I say, the internal interpretation of motives of any German.
Certainly not, an objective interpretation.
An objective interpretation of the motives. I mean, I don't think he would ever have distorted facts.
No, but his interpretations were colored.
His interpretations, when they weren't fact-dependent, weren't constrained by the facts, were, I think, inevitably colored, and I don't count it against him, for that —
— no —
— if it is so, yes? You probably have read more, do you concur?
Yes. He, for example, the first time the Alsos mission captured an appreciable number of documents was at Strasbourg, but they didn't capture actual scientific papers, but they read through von Weizsacker's papers —
— I saw, there was a fascinating letter, carbon copy, I think, whether it was a carbon copy, I don't know, but my memory says it was, letter from to Houtermanns to Weizsacker.
I read that.
Calling attention to the fact that if you accept the Bohr-Wheeler ideas — I think he — I'm not, please, remember this is 40 years — 40 years have elapsed.
If I ever refer to it, I will say, "you remember the letter".
Anything that I remember of the letter after 40 years may be fiction, OK? But as one remembers things, but not totally, and then one tries to reconstruct the missing bits of what one remembers, and next time after a lapse of ten years you try to remember it, and what you think you're remembering from the original may be one of your own reconstructions, in the interim, rememberings, right?
There was a letter, Houtermanns to Weizsacker, drawing on the Bohr- Wheeler paper, plutonium, which would be made by the running of the machine, the reactor, a peaceful energy reactor would generate plutonium, plutonium would be an artificial element and would be chemically extractable without having to go to the more difficult processes, physical processes of isotope separation. And it looked as though Weizsacker had filed that away and done nothing else about it.
No, that's not quite true. Weizsacker wrote up a paper, about the possibility of this, and it was dated summer of 1940.
‘40, however, I don't remember the exact date. I don't remember the date of the Houtermanns to Weizsacker letter, but it would probably have to be later than '40, wouldn't it? Because in '40 Houtermanns would be in jail.
That's true. Well, he came back, he started work in Berlin January 1st, 1941, he came back some time in 1940.
Well, the story there is that Houtermanns spent about 2 1/2 years in a Russian jail. He was picked up in the Tukhachevsky purges, where anybody in Russia who had any German contacts was popped into jail, and kept in cold storage so they could try to interrogate, and after he had been about 2 1/2 years in jail, I think in Kiev, he was brought to Moscow and was interrogated by a senior general, I heard all this from Houtermanns himself, I spent a happy evening with him, when he was describing his prison experiences. It would have been in Goettingen, well, I don't now know whether it was '47 or somewhere between 1947 and '50 —
Just after the war.
Just after the war or possibly another couple of years later, I forget, so, the Russians popped him in jail, and after 2 1/2 years moved him up to Moscow, and then for the first time he was interrogated by an intelligent person. Up to then he'd just been interrogated by policemen who brought him confessions to sign, and he used to read through the confessions, and if it incriminated anybody else, he refused to sign, if it incriminated only himself he saved time by signing. At last however he was brought to Moscow, and interrogated by a KGB or whatever it is general, and the conversation began by saying, "Well, what are you actually guilty of?" And he said, "Do you want the truth?" "Yes." He said, "I've been 2 1/2 years here and this is the first time anybody's asked for the truth. Truthfully, yes, I have deprived the Russian state of one pair of underpants, by expunging the state's mark on it, with the aid of bleaching powder."
He'd deprived the Russian state of one pair of underpants?
One pair of underpants, by expunging their mark on it with the aid of chloride of lime, and that was the only crime he was actually guilty of. The KGB general believed him and said, "Well we'd better get you out. Where would you like to go?" He said, "Anywhere but Germany." "How would Sweden suit you?" "Yes, I'd love it." So he was moved back to the Lubinka and was shown into a much better cell than the one he'd come from. And the prison librarian came along and said, "Can I get you some books from the library?" and then nothing happened for another couple of months, they brought him a piece of paper to sign saying he had no complaints against the Russian state and he signed it. And then he waited for his transport to Sweden, but unfortunately the Ribbentrop-Molotov Pact intervened, and they had an agreement to swap prisoners, and the Russians would send all the Germans — he was an Austrian, I think, but Austrians were Germans by then — and then the Gestapo would send any Russians they held to Russia, and so instead of going off to Sweden, he was popped into a cattle truck and arrived in Germany and went to the Alexanderplatz where he spent the next six months in jail, and then von Laue managed to get him out.
He got him a job with von Ardenne.
Worked for — very likely. I never really got any close knowledge about von Ardenne. See, I knew that setup under the post-office; it had von Ardenne, who was really a most inventive engineer, and Siegfried Fluegge.
von Ardenne was a very good businessman.
Yes, must have been, because he was one of the very few people who managed to live on his patents before the war broke. He made a scanning electron microscope, I've seen that. That was in his own house. I've visited it. He had a laboratory in the basement of his own house, basement and the garage, he had a scanning, certainly by decades the first scanning electron microscope ever was. Anyway, Siegfried Fluegge, who was a very good theoretician, and von Ardenne, a very good inventive engineer, couldn't be a negligible set up.
I thought that Fluegge was still with Hahn's Institute. 
No, the Institute got dispersed. Hahn was with the, Hahn went down to the Black Forest.
That was much later.
Fluegge might have been there later. I didn't know for a fact, I wouldn't know where Fluegge was in 1940, but at the end of the war, Fluegge was not in the party that was collected.
Well, Hahn's Institute was evacuated.
Hahn's Institute was evacuated, and the physicists, the two institutes involved, the Kaiser Wilhelm institut fur Physik, which Heisenberg was the head of by then, of course before the war Debye was the head, and Hahn's, where the fission was first, experimentally discovered — there's a nice autobiography of Hahns, in which he wrote a quantity of letters in December, what? December '39 I think.
December,'38 to January '39, just before — which throws quite a different light, [on the discovery of nuclear fission] at least as far as I was concerned. Up to then I had believed that all the experiments had been done by the Hahn group, Hahn and Strassmann, but they had been misinterpreting it all along, and it was Lise Meitner and Frisch who reinterpreted their results. But it's clear from that correspondence that really Hahn got there before them, but only just.
But he was very cautious.
He was very cautious. In the earlier letters, he was saying things like, "I know the nucleus cannot split into two" or words to that effect. "I know —" somebody must have told him, on theoretical grounds, but they were wrong, that the nucleus couldn't split, "I know it cannot but it looks awfully like it." And the final letter, in December '38, without being told by them, by Meitner, he said, "There really has to be fission."
Frisch and Meitner gave a very clear theoretical interpretation of fission, and they published it. I think it's true that Hahn knew what was going on.
I don't know why in December, '38, he was so positively against the possibility — you know, the earliest of those four or five notes. I don't know why he was saying so positively, "I know it cannot," because about a year earlier, I can remember a conversation in an U-Bahn in Berlin going back from a colloquium at the university there, going up to Dahlem with Fluegge present, I'm almost certain, and Strassmann present, I think, anyway, very good people present in this conversation, and I think probably Wefelmeier talking about sausage-shaped deformations of the nucleus. Once you start thinking about the nucleus sausage-shaped deformed, you must be thinking, you're almost there to saying, well, there's Bohr with his liquid drop model, knowing that Bohr had a liquid drop model, telling yourself it forms itself into sausage shapes — it may be that Fluegge didn't believe, and Fluegge was present at the conversation but perhaps he was more orthodox in his thinking and listened but didn't accept that.
It's easy after the fact to see that fission is clear, it's obvious, we should have guessed it before.
But the fact is that up until then, no one had thought about fission. Everyone had thought of chipping things off nuclei.
Yes, but once you start thinking about liquid drop and sausage-shape deformations thereof, —
Ah yes but…
— I mean, I can remember it well, the words "Wurstfoermig".
For example Bohr, who worked out the liquid drop model, didn't start thinking about fission until he was told about it.
Your point is right that once they seemed there to be thinking about the liquid drop model and fission together —
It's merely this authoritative sentence which is in one of the Hahn letters in his autobiography, yes, that may be the beginning of December, '38, where he says, "I know it can't." Why did he know it can't?
I guess either a theorist gave him his considered opinion on the matter, or it was just so novel.
He was cautious. As you say, he was a cautious man, and I think a good scientist, a cautious man is cautious about negative, making negative statements positively, as well as making positive statements positively, yes? So, that puzzles me a little bit. Anyway, there we are. I'm really saying things like this so that —
Well, it's all very interesting.
I want you to realize that I knew the people.
Yes, well, it's very good.
I was in conversations, at the time when there were thought to be trans-uranics that the Hahn group was discovering, and it was not my subject, but I knew the people, and in scientific conversations like in the underground train going back from the colloquium down Dahlem way, I listened in to these discussions, and I'm somewhat familiar with the people concerned. All right now, where are we? About enough, just to get back on it — oh, coming to the end of the war, OK, then we were involved in a small way, oh yes, Eric Welch, I presume you've come across his name? Well, we had things to do, Eric Welch at the time, he was a Secret Service man from Norway, when they were planning the raid on Norsk Hydro, in which the Secret Service of Norway was involved Welch was very much involved in the Air Force. And I personally had to go and explain to the chief of the Air Staff why it was worth sparing some airplanes, some bomber strength, for this raid. OK? Now, I didn't know whether Portal had — I expect somebody had told Portal about nuclear bombs, but at any rate, he kept a straight face and just asked me what this was to do with it and what would a nuclear bomb be if one came about, so I gave him from scratch a child's guide to what a nuclear bomb is. Then when the party went behind the — the Anglo-American party went round behind the German front, to pick up the Black Forest gang(?) in front of the French, properly speaking, that piece of the front was French, right? But —
— that was set aside —
But the Anglo-American party went round behind them and —
— That was the Alsos Mission with Goudsmit and Welch.
Welch was on that party, I think. And Frederick Norman was. He was really a literary man, a code breaker, a professor of German, a good German linguist, and virtually a member of our staff. He was actually a literary man with whom ADI science, commonly me, talked at least once a day direct, so he was one of the parties. I'm not sure whether Hugh Smith was. I don't think he was. At any rate, we were involved, but by this time, we'd more or less pulled the things together, and Akers had more regular connections with the American side. I guess then one week in Sam Goudsmit's office in Paris, but the closest and continuing connection was [Michael] Perrin and Welch, and Perrin more or less made himself the anchor man for intelligence about nuclear energy. So that's that. So when they were captured, when they were put into Farm Hall —
Were you actually there, did you actually go to the Black Forest?
No. No, I told you from ADI science, I think Frederick Norman was the one, I forget whether Hugh Smith went, I don't think he did, Frederick Norman certainly did, and I couldn't really regard Eric Welch as one of our team. He was a team we worked with, right. But Frederick Norman, though he was a literary man, I could regard as one of our team, so that was the nearest we ADI Science were engaged in the actual fighting, going behind the lines to capture those people. When they were brought to Farm Hall, it was at Eric Welch's suggestion that I went out one day to have lunch with them.
This was before or after Hiroshima?
It must have been before, I think.
40 years have elapsed, true, perhaps I'll get the thing wrong, but I think the lunch was before. Perhaps it wasn't. One thing I do remember is that after lunch, Wirtz and I had been great friends before the war, we had made trips, gone skiing together. I knew his sister. We made a trip to a scientific conference in Graz and on the way to Graz stopped off for a couple of days in Prague and a couple of days in Vienna. So I knew Wirtz fairly well. And oh yes, we were, in fact, we were calling each other "Du", and he noticed it when I had lunch with them and starting calling him "Sie" again. He took me for a walk after lunch. Wirtz and I went for a little walk in the garden. He thought we could speak more comfortably out on the lawn, because that place might be bugged. Somewhere in a cupboard they had found some wires which they didn't know the reason for. So they suspected the bugging of Farm Hall. Now, here comes — I have had letters from Wirtz rather recently, and he denies what I thought he told me.
Tell me what you remember.
I thought he told me that in — you see, I know something from — this is where I begin to wonder, was it before or after Hiroshima? I thought he told me, I put together the two bits of evidence one, the recordings of their conversations, Heisenberg's seminar after Hiroshima, and what Wirtz told me on the walk in the garden. And it may be that I have partly transferred the evidence from one source to the other. After 40 years, nothing one remembers is utterly right.
That's true, but this is exactly what I would like to hear.
I think he told me that in 1940, the German physicists held a private meeting of physicists to say, what are we going to do about nuclear energy? What would our policy be? And they came to the conclusion that as far as physics was concerned, their policy ought to be to preserve all, as many as they could, good physicists from being sent to the front and slaughtered in Russia. So far as Germany was concerned and so far as — oh yes, the bomb. The bomb possibility. Heisenberg at that meeting gave what I call his back-of-the-envelope calculation, which led to the conclusion — here I don't know whether it led to the conclusion, that the critical mass of Uranium 235 would be five tons or nine tons, but anyway, a figure like that. Tons. It was an explicit number, as it was told to me. Or as it appeared in the seminar he gave, because he begins his seminar with the back of the envelope calculation, and then says "We've to reconsider this". And Heisenberg worked it out that the critical mass of U-235 was so large that neither the German side nor the Western side — nobody, neither Germany nor anybody else would make a nuclear bomb within the maximum putative duration of the war. So the bomb as such could be neglected and disregarded, and the sensible policy for Germany would be to go for civil nuclear power, so that when the war came to an end, Germany would be in a position to lead the world to civil nuclear power-reactors, OK? And I'm under the impression that I was told that this was in 1940. Well, then fairly close to this, then is Hiroshima. The date of my lunch, I'm telling you, I think was before Hiroshima, it may not have been. Then I didn't visit them again but I read the tapes, I expect they were wire recordings. I read the transcripts in German from the recordings of two episodes, one being the immediate reaction to the radio news of the Hiroshima explosion, at which Hahn was obviously very deeply shocked. Everybody was surprised. Hahn was deeply shocked, and emotionally disturbed. Hahn said that it had worried him very much, as soon as fission, as his experiments were interpreted as showing fission, he had been deeply worried, and then he'd been sort of reconciled to the situation when he was made aware that slow neutrons would be captured and he thought that it [would hinder the chain reaction]. Now, the difference between fast and slow neutrons brought it about that you would not get a runaway explosion in uranium and he had thought that neutron capture making non-fissile elements had relieved him of the burden of inventing the most destructive tool ever discovered by man. So somebody, what Houtermanns told Weizsacker or Weizsacker probably knew before —
— or independently —
(crosstalk) If you have evidence that Weizsacker knew about it in 1940, it follows that the reason why he didn't pay much attention to what Houtermanns told him was, he knew it already.
Houtermanns ultimately later wrote his own report in '4l about the possibility. And I think Houtermann's is more clear that Weizacker's. But it seems they did it independently.
OK. But they hadn't told Hahn.
It doesn't surprise me. Heisenberg thought very much always of his inner circle, and when you spoke to Wirtz and Weizsacker and they spoke of the project, they really meant Heisenberg's inner circle. Things passed from Wirtz to Weizsacker to Heisenberg, but they didn't necessarily pass to Hahn and Bothe and others.
Bothe wasn't in the same gang. (crosstalk).
That's the distinction. They speak of their gang.
But Hahn was with them. Was it Hechingen (crosstalk)? Where did they build their pile?
The pile was in Haigerloch. Bothe had worked on some of the reactor experiments, but he'd already been captured in Heidelberg. He'd already been arrested before they got to Hechingen.
Was Bothe at any time in the Black Forest? I didn't know he was.
He visited. Heidelberg isn't that far away.
I had thought that Bothe ran his own independent —
They were all independent. There were several groups.
At any rate, perhaps I'm over-influenced by the fact that when they were collected, let's say the Hahn people, Hahn and probably one or two other Hahn men, were with the Heisenberg group. Heisenberg himself was away in the mountains in the south and a separate expedition had to go and fetch him.
A good example of what I mean by secrecy, you know a man named Hiby? He was also a friend of Wirtz, he was an engineer, he was first in the army, then in '43, during the so called "Osenberg action", when they withdrew a few thousand scientists and engineers from the army, Hiby was able to come back, and he came to Dahlem and he received the task of organizing the evacuation.
— I thought Osenberg was nothing but a fraud.
Well, he was but he was in the SS, and thus...
I know he was with the SS, and the group that he knew, the Americans, the Americans were employing Osenberg.
Oh yes, I believe it.
The week that I spent with Goudsmit, one of the things he showed me in his files, I don't know where he found it, I found it in the files which he handed me to look at — the explicit occasion of my visit, my spending a week with Goudsmit in Paris, was that Alsos had such a secret briefing letter... (off tape)...was saying, "This bloke is impounding papers which might be of great importance to us, and so my brief overrides everybody's," and his briefing letter couldn't be shown even to Eisenhower, so there was a lot of jealousy. The American Air Force and the British Air Force and so on were saying, "There are important intelligence papers going into that office and we can't get at them." And so I was sent from Air intelligence to spend a week with Goudsmit, to see whether it's true. I was able to report back, nothing of importance that was really relevant to Air intelligence was being secreted there. So anyway, I remember seeing a photograph of Osenberg with an SS badge on his lapel. And we were rather shocked. He was at that time being employed by American intelligence — a good source of information for everybody. But I never thought he was anything but a, what should I say, an impostor.
But he did do one thing that benefitted a few thousand German scientists. He appealed to Hitler, a version of the argument was that 5000 less soldiers won't affect the war effort but 5000 more scientists could win the war.
And he appealed to Hitler and won the right to withdraw the scientists.
(crosstalk) a good empire-building move —
Yes, it was, it helped him personally, as well.
But one of the consequences, presumably, at least it's likely, is that, several, some substantial sum, a not insignificant part of the German uranium oxide was in the possession of the SS, and the pile, Heisenberg's pile never went critical, and would have done if they'd only added one or two more bricks of uranium oxide.
Well, the SS as far as I know had never had any interest in the project. However, there was (crosstalk) Diebner's group.
— there was in this group —
Diebner, he was in the party and the army, but he had nothing to do with the SS.
Wirtz told me, this then is part of the conversation in the garden, that there, they built their pile, and they didn't have as much heavy water as they, it was a uranium oxide (crosstalk). [pile].
No, the last one was metal uranium cubes in heavy water.
I thought it was — oh well, it doesn't matter. Oxide, graphite and heavy water. They had less heavy water than they meant to have, because of the sabotage in Norway, and they got to a point where, when you put in a parcel of neutrons they decayed slowly, did not grow, and two or three more bricks of uranium oxide, I think he said, would have made it go critical, and that was 150 miles away in the possession of the SS, and they had authority to take it, but for several weeks the railway lines were bombed out, so they never got this, so they never actually got their pile critical before the war ended.
As I understand it, it wasn't the SS, it was this group led by Diebner who Wirtz did not like that was at all, Wirtz was implying, if they had had another trial, they wanted it to go critical.
... [It] wouldn't have affected the outcome of the war, but certainly would have been an achievement.
Wirtz was planning to stick blocks of uranium oxide in the graphic mantle, hoping that that would kick it up just enough to make it go critical.
Well, where are we now?
I was just going to get to this example of Hiby, because he came back from the war and was put in charge of the evacuation of Heisenberg's Institute, to Hechingen. He was the person who took over the land, the buildings, set up the experimental apparatus, took care of all the transfer of people, of equipment, everything. He never asked what the research was about, and he was never told. He was a very close friend of Wirtz, they were also on "Du" terms, and he said that in those days he had learned not to ask. But being the very person who set up the equipment, he had a vague idea that this had something to do with a uranium-heavy water design, which would produce energy, but he was never told what went on.
Yes, well, I'm very well aware of the situation. I know that when we came toward the end of the war, we captured some German radar people. We had a far better conspectus of the whole German radar system than any German radar expert.
Yes, that's the way it was in nuclear research as well.
So, I want to get on to something. Yes. Heisenberg's seminar as I remember it, it began with the back of the envelope calculation, saying, this is how we worked it out, I think he said in 1940, but I could be wrong about the date in question. "This is how we worked it out." Do you know the argument?
Yes, I've read, wasn't it in R.V. Jones's book? The "drunken walk" argument?
That's right, yes.
It's a very crude argument. You'd expect someone to do it in very little time on the board.
Yes, it is exactly like back of the envelope, it's brilliant. I mean, it's disappointing it gives such a false result actually.
It's brilliantly simple, and had it given the right answer, you would say how clever, it takes a clever man like Heisenberg to see how to do such a difficult problem so simply.
See, the distinction is between requisite and necessary. This Heisenberg calculation would indeed work, that is enough uranium for critical mass, more than you need.
Yes, but it's more than you need by factors of the order of a thousand.
Yes, but that comes from the critical radius.
It comes from not wasting a neutron.
Yes, but if you look at the critical radius connected with these two masses, it's only a factor I think of ten or fifteen.
Yes, sure, a factor of ten raised to the power of three, and you go back, that's right, but it goes this way, you're not wasting a neutron.
So the argument — to make a sizeable bang, we want something like 1024 atoms of uranium.
And 1024 is something like 280, and you double your number of neutrons with each fission, and therefore 80 generations of breeding in the chain reaction will get you up to 1024. But 80 steps of generation, we should be, square root of 80 times a mean free path away from our starting point. Square root of 80 is 9, and the mean free path I think he said was 5.7 centimeters, probably wrong, doesn't matter.
On that order.
And therefore we get a radius, let's say, of about 50 centimeters, and that will weigh seven tons. That's, as I say, had it not been that it gives you, in the end, a significantly wrong answer for practical conclusions, everyone would have said, it's the brilliance of Heisenberg to see a simple way of calculating it. He did not know that the right way to calculate it had been published by Peierls in the Proceedings of the Cambridge Philosophical Society, in the September issue of 1939, which however did not actually get published until December. And presumably didn't reach Germany.
No, I've also talked to Peierls and he got on the problem because of a paper by Perrin.
I can't pronounce French. It's spelled like Perrin, but
Perrin, oh yes, —
And Houtermanns in his paper, in his pretty exhaustive paper about the theory of chain reactions in which he also mentions the possibility of making trans-uranic elements, he mentions Perrin but not Peierls.
But had he done what I call the, I've referred to the back of the envelope calculation and the tripos paper calculation, Cambridge mathematics examinations are called tripos, right, so the two standards of calculation, it is just about a tripos level. It's the kind of piece of applied mathematics that you would expect a chap who's really trained himself and brought himself up to the point of being able to take the tripos examination at Cambridge should be able to do it right that way. And say possibly take an hour to work it out. OK? Considerably more to work it out than back of the envelope calculations. So the seminar began with the back of the envelope calculation, and then followed on with the tripos calculation.
Which was much more sophisticated.
But it's only that much more sophisticated, that, I say it is at about the level of a Cambridge mathematics tripos examination question.
Although in a sense the problem isn't that complicated.
Yes, but still — the right way to do it.
You would say that Heisenberg's tripos version was comparable to Peierls' published version?
I guess so. Well, I'm not quite sure now, on some occasion I thought he did it overnight, after the news came in on the radio, and Heisenberg immediately saw that the estimate was wrong — right, if the Americans had made such a bomb, that it couldn't be a mass of five tons, a critical mass of five tons. And I — but have since been told by several people, you're not the first person to come and quiz me on history — that actually it was several days later that he gave the seminar.
Not that big a difference.
Overnight or during two or three days that elapsed, after, he did the calculation right and gave them a seminar that showed pretty well what the critical mass should be. And I certainly got the impression from that seminar that it was brand new, this was the first time he'd done it. That he'd been content with the back of the envelope calculation for about four or five years, and had not looked at it again, and —
I would believe that —
— but the difficulty is that they also say, Bagge isn't it? that sometime in mid-war, Heisenberg told the German military that the nuclear bomb would be about the size of a pineapple.
I'll tell you the evidence, Goudsmit's book contains some inaccuracies, for example, which the Germans didn’t know about plutonium, but Goudsmit wrote his book before reading any of the scientific papers, he admitted that later.
Yes, but Goudsmit had certainly seen Houtermanns' letter to Weizsaecker about plutonium, before he wrote his book. He showed me the letter while the war was still on.
Well, Goudsmit, like many people, Goudsmit thought of Heisenberg as being the only one who counted.
Yes, the Germans were like that.
But in the book Alsos Goudsmit says, basically says, the point of the book is that Fascism, Nazism ruined German science, look at the German atomic energy project, they didn't even know how to build a bomb with fast neutrons, they didn't know how to make plutonium, claims which are absurd. But he wrote the book without looking at the scientific papers. Carefully, as he said himself, and he was very cavalier. You were there, but my impression is, that he was very cavalier and once he decided in Strasbourg that there's no danger of a bomb, he didn't pay much attention to it afterwards. Heisenberg was not pleased about this book being, well, of course, the Germans —
— well, what Goudsmit said, about what Goudsmit said?
The German scientists were in a difficult position. On the one hand they were accused by their foreign colleagues of working for the Nazis.
And also being accused by their scientific colleagues, at least by Goudsmit, of being stupid.
Stupid. Then a third aspect is they were accused by Germans, patriotic Germans, of having failed the Fatherland. They said maybe the Nazis shouldn't have won, but Germany shouldn't have lost. So they were in a dilemma.
Who were — anybody I know, any scientists who were — [of the latter opinion]?
No, not scientists, that's the point, it was the popular opinion. So they had to tread a very fine line, and their response was, which became dogma, is Heisenberg's article in Die Naturwissenschaften and NATURE in '46, '47, that he never tried to build bombs, we over-estimated the technical difficulties involved. Now —
— I think they did. I believe it's a correct estimate. The amount of effort, trying to do it by either of the routes, the reactor plus chemical separation, or isotope separation, I think it's a correct estimate, that Germany — the actual duration of the war being what it was, Germany could not have afforded the effort to do it. That's my judgment.
Yes, I would agree. However, at the time, you have to consider the audience Heisenberg was writing for, he said, "We never tried to build bombs. We slightly over-estimated the technological difficulties involved. But of course we think now, it would have been horrible to have given such things to Hitler." That way, they said, "We did good work, we didn't think it was possible," and although perhaps a rational scientist could see that indeed it wasn't possible, for the popular consumption it was a little different, and the Americans said, "Well, why didn't the Germans try?" "Well, we over-estimated a little bit." And that got them out of the problem nicely. But then, that was in public. In private, Heisenberg wrote Goudsmit and pointing out that "if you looked in this paper and this paper, which you surely have because you took them from my lab, you can see that we knew about plutonium, fast neutrons and so on and so on." Then Heisenberg got very cagey, about critical mass. What he says in the letter is, and this is seven years after the fact, in 1949, the conference is in '42, that he reports of, June of '42, Speer and the various generals, Milch and others — Heisenberg said, "Now, I can't remember exactly. However, Ernst Telschow, who was in the Kaiser Wilhelm Society — "
— yes, I knew him —
— "remembers —"
— he was sort of top civil servant of the Kaiser Wilhelm Society.
— "Telschow and a secretary remember that I had been asked by a general, how big a bomb would be? And I said, 'Oh, about the size of a pineapple,' and this caused a commotion among the non-scientists involved, and I hastened to point out some of the difficulties." And that is it. There's a book on the subject by David Irving.
Yes. He's a very assiduous man at digging out things in difficult places.
That's true, I guess I owe him a debt in that as a short cut I read all the sources he used and I'm finding more. There are no foot notes in the book. Rather, in the back there's just a list of sources. Now, I read his book carefully. I read all these sources. And his book is misleading in that some information is taken from a document in 1942, and some information is taken from an interview with Heisenberg in 1966, when Heisenberg's memory wasn't all that good, and he had reasons to stress certain things and reasons to, I don't want to say make things up, but to stress things to the total exclusion of others, such that an utterly false view is given. And if you read Irving's book, you can't tell what's valid and what isn't. And this pineapple — he also mentioned the pineapple story because Heisenberg mentions it, and Telschow remembered it, and this Telschow business is very dubious. Another time, he was asked —
— well, Telschow is not a scientist. He was a top administrative officer of the KWG.
But also Telschow was asked at a later date, about this pineapple. He was asked by a pro-Heisenberg German historian and, "Do you remember this?" He said, "No, I don't remember it." And then finally as the German historian himself said, "After prompting, Telschow admitted that perhaps he remembered that."
It's the one thing that's worried me. Inconsistent with the evidence that I knew of.
Well, there's one other thing, and this is very new. I mention it because I think you'll find it very interesting, this is what I meant when I said, you have to make a distinction between Heisenberg's group and all the scientists working in general on this problem.
Because the first three years of the war, up until October, November, '41, the German project was loosely under the Heereswaffenamt — the army — and Diebner who was the army's physicist was technically in charge. He was acting director, head at Dahlem and so on.
Where in Dahlem?
He headed the Kaiser Wilhelm Institute for Physics. He was acting director. In '42 Heisenberg came and was appointed director at the Institute.
I see, the director to the war was Debye, Diebner filled in for, what? A year and a half, two?
Almost two years.
Then Heisenberg became director.
But in December '41 the army, this was after the first Russian counterattack on the Eastern Front and the Blitzkrieg was over, and the army reconsidered whether it really needed a nuclear physics project, which was a reasonable thing to do because it suddenly became clear that Germany needed an ordered war economy. They hadn't bothered before, as you are well aware. And Schumann who was the head of the research section of the Heereswaffenamt.
— all right, I haven't a clear picture of Schumann.
A descendant of Schumann the composer. He called this — Institute heads, directors, to a meeting, and said, "This sounds very interesting. It's good that someday we may have a lot of energy and very powerful explosives, but will it affect the outcome of the war?" And the scientists said, "No," and so the army made a very reasonable decision, and they transferred the project to the Reichsforschungsrat, Reich Research Council, which is the site of civilian research.
Right. And the scientists themselves, were concerned that the Reichsforschungsrat wouldn't be as good a sponsor and so on, so they scheduled a huge conference in February of '42. There was a public lecture series and Heisenberg gave a talk, Hahn gave a talk, and there was a large lecture series among all the scientists doing anything connected with this problem, a conference among themselves, 40 different papers, OK. Now, in a sense the last thing the Heereswaffenamt did, several scientists, the physicists on the Heereswaffenamt staff wrote up a review article of all the papers published up until that time, 150 pages and I don't know exactly who wrote it. It was either Diebner or someone on his staff, but it's clear by reading, I've read the article and I've read all the other papers, and it's clearly authentic because it comments on all these other articles. Indeed it couldn't have been written after the war because the Germans didn't have these original papers.
OK, in this paper, it doesn't mention Heisenberg's 1940 back of the envelope calculation, secret meeting, but it does mention...
Wirtz now denies that there was any, in the last letter I had from Wirtz, he denies that there was, he has no knowledge or memory of any such meeting in 1940 or anything else which can feed into that.
Well, that's irrelevant — it's not the remembrance, the seminar's enough. But the point is, what you'll find interesting is that, the possibility of pure uranium 235 and plutonium and explosives I mentioned, Heisenberg's work on nuclear reactor design, and they talk about critical mass, but it's not Heisenberg's estimate. The scientists who wrote this up said, "And the amount of substance needed for a bomb would be roughly 10 to 100 kilograms," which is quite reasonable. So the point is, I have proof that not necessarily Heisenberg, not Weizsacker, but someone among the German scientists was quite aware of what a likely estimate would be. But they also thought that it wasn't likely to affect the outcome of the war, which is reasonable, but the point is, once the army was squeezed out, once the army left, Diebner withdrew in '43 and ran some of his own experiments, in fact, there were two competing groups, Heisenberg's group, Diebner's group, by this time.
What about the post office group?
Well, the post office group died early, the thing is, they were setting up an electromagnetic separator, and a cyclotron, but in 1943 they were all bombed flat. That sort of was the end.
Then the post office scientists, in the last years of the war, went to other labs. They had to leave in any case because Berlin was being smashed flat.
Yes. But they were in Berlin. The Russians picked up, at the end the Russians picked up von Ardenne and Fluegge.
No, no, not Fluegge. I don't think, to be honest with you, I don't think Fluegge was there.
I was told, maybe the I was erroneously told...
Gustav Herz went to Russia, von Ardenne went to Russia, a man named Nicholas Riehl...
I can't pronounce the German R correctly.
Riehl, Riehl, no, I don't know him.
He was working at the Auer Gesellschaft, the company which processed the uranium during the war.
Then he went to Russia for ten years. Then he came back to Germany and he took a position at the Technical University in Munich and he's still there.
I was in Gottingen in '47?
He was in Russia, working.
I think I've been told that Fluegge had been picked up by the Russians. Maybe I was erroneously told?
No, Fluegge, as far as I know, he may have been, I don't think he was in Berlin. I think he went with Hahn's Institute, but he never spent time in Russia.
Neither the British nor the Americans ever picked him up. I thought the Russians had him.
No. What do you mean by picked up?
He wasn't in Farm Hall and also he wasn't in any other — if he had been a prisoner, I think I would have got to know and would have wanted him brought in for —
Well, for example, Bothe wasn't.
Walter Bothe was at Heidelberg and he was regarded as an academic scientist.
OK, well, at any rate —
I thought Fluegge got caught by the Russians and it was several years before he got back again, but that's an error, is it?
I think so.
Bewilogua, you know anything about him? He doesn't count. When the Germans, when all of the nuclear people, KWI fuer Physik, went down to the Black Forest, Bewilogua maybe was looking after the lab, I think.
Yes, I've seen the name.
He was, well, one of Debye's — and Debye's right hand man for getting on with, you know, scientist, for getting on with his administration of the department, where van der Grinten (ever heard of him?), who was running the high voltage machine in the KWI fuer Physik, And van der Grinten was in charge of that. I forget what Bewilogua actually did. Oh, something with dielectrics? It was one of the people who I thought were taken by the Russians and never heard of again.
As far as I know the German nuclear scientists who went to Russia to work for the Russians were Riehl, von Ardenne, Gustav Herz, and a man named Barwich, he was an assistant of Herz. He came back and he escaped to the — well, he went back to East Germany originally, when he could have come to the West, but then eventually he fled to the West and he wrote a book called Das rote Atom which is about his time in Russia and so on. And Doepel who was at Leipzig under Heisenberg — Robert Doepel.
And that's about it. Thiessen who became head of the KWI in physical chemistry after Haber.
[He] was head of the — head of KWI fuer Physikalische Chemie the old —
— Haber's old — institute.
— and was a Nazi, of that group of KWI laboratories in Dahlem, he was the boss Nazi, and as soon as the Russians appeared, he went over and presented himself to the Russians and offered his services.
And they were willing to take him.
Right. Anyway, I'm sorry, I interrupted a story of yours, I believe.
The point is that one has to remember that there were other scientists besides Heisenberg's group, I believe very much that Heisenberg made a quick calculation of critical mass and let it go. I've looked very carefully at his work on nuclear reactor design and he did the same thing. In late '39 he wrote his first report. In early '40 he wrote the second report, and he made a simple design where he used horizontal layers. And that became dogma pretty much. Heisenberg didn't do a single thing more. He wasn't interested. It wasn't scientifically interesting for him. He worked on cosmic rays. He worked on his S-matrix theory. The only other reports he wrote in connection with nuclear energy were reviews of other people's work.
He became head of the Kaiser Wilhelm Institute of Physics in Dahlem. He was critical of the nuclear research because of the science policy position.
But he didn't do a lot of work on it. After the war, when Hiroshima was obviously so important, the impression he gives is that this was crucial and we all thought about it very much. But in point of fact he spent precious little time on it. He stopped his creative effort on nuclear reactors in 1940.
So I have every reason to believe that he made a quick estimate on critical mass and let it go.
And no one questioned this until Diebner worked out a different design, a cube design, a crude cube design.
A simple cube lattice. I have a vague idea that I knew him [Diebner] but he doesn't come back to mind.
He was also —
Was he in Farm Hall?
Yes, he was, he was the one that no one else talked to. Diebner made a slight change, instead of layers, solid layers of powder or oxide or whatever, he made layers of cubes.
Now, it's not quite a perfect three dimensional lattice, but it's on the way. Now, Heisenberg, sent the youngest physicist in Dahlem, Karl-Heinz Hoecker, a theoretical physicist...
Well, he sent him to see what was theoretically behind Diebner's change and he proceeded, rather than simply to analyze his [Diebner's] experiment, he proceeded to do, which Heisenberg had never bothered to do, and methodically looked at the theory of the geometry of the nuclear reactor. He eventually decided that spheres are better than layers designs, a practical compromise would be cylinders, which of course is what is used today, nuclear power, and he said that Diebner's experiment, could be interpreted as spheres and that the best machine would be roughly a three dimensional lattice of cubes and heavy water, and he wrote it all up, sent it to Heisenberg, and Heisenberg ignored it. Basically and for another year Diebner did two more experiments, and the final one was a lattice of metal uranium cubes in heavy water. That was a three dimensional lattice, and that experiment was much better than anything the Dahlem group had done.
In these things I found a letter from Wirtz to Heisenberg, and it says, "I just talked to Hoecker in Strasbourg, he explained his theory to me. He argues that a cube design will always be better than a layered design, and I'm not going to say that I'm sure he's absolutely right, but it might be perhaps that maybe we should not use layers in the next experiment, and Hoecker at my request, is sending a copy of his calculations to you, and Heisenberg basically said, "No, we'll go with the layers." That was in 1944. They did a few more layer experiments in Dahlem. The last ones in Dahlem. And then sometime in late — sometime around 1945, Wirtz got his way and they set up what would be their last experiment, with cubes in moderator. So the point is that I believe very much that Heisenberg made this quick calculation.
— it's incredible —
I wouldn't believe that he would spend so much time on the critical mass of a bomb when he spent so little time on a reactor because he saw, once the possibility of plutonium came about, he was convinced that plutonium —
I'm a bit surprised that Heisenberg did not — I would have thought, you see, that Heisenberg would be happy with the general calculation that gives you the answer in principle, and would be well aware that a proper engineering calculation could lead to a better design. I would have thought, but it wasn't for him, it wasn't for the likes of him to spend the great amount of effort, rather a tedious calculation, unless you could find some clever way of demonstrating the theorem that cubes or spheres were going to be better than layers. That I would have thought ought to have been enough to catch his interest on a point of principle. But I would never expect Heisenberg himself to spend a long time on the engineering calculations. I'm a bit surprised that Heisenberg didn't respect superior engineering calculations.
He, well, in his '39 paper, when Heisenberg discussed, well, there's two kinds of designs. One is a homogeneous mixture of the uranium and moderator, the other is to separate the uranium and moderator, OK, then he works out the theory of both designs. He decides, what's the best separation design? Obviously horizontal layers. Why? Basically, he took a lot from neutron diffusion theory already worked out by Fermi and Fluegge.
But he didn't have much time. He wrote two reports and finished with the job.
By the way, I can give you an analogue, in the theory of superconductivity. There is a paper by Landau and Ginzburg on superconductivity, I think, discusses the superconductivity of a thin layer. Actually it was perceived that there were two classes, type 1 and type 2, and then the paper of Landau and Ginzburg, which explains fairly basic principles about type 1 and type 2. They then discuss the superconductive behavior of a thin layer of type 2 superconductor, with a magnetic field, an external magnetic field outside it. And they describe a wave function quantity, quantum mechanics. It didn't affect the paper, which says, you know, obviously really this is a quantum mechanical phenomenon, instead of talking about the concentrations of superconductive and normal electrons, we should talk, we should introduce a quantity which could be quantum mechanical, call it psi, and then he discussed the behavior of this thin sheet, and then they say, "Obviously psi must be a function of z they called it, normal to the layer, OK, and they arrived at a certain result, for breakdowns of superconductivity by a magnetic field, and then comes Abrikosov, young research student writing his thesis, under Landau, who discards those parameters, psi function of z and allows it to vary with x and y also, and discovers the Abrikosov lattice, so called vortices. OK? Takes it to Landau, and Landau says, "Oh, no, that's taking the Landau-Ginzburg equation too seriously," and wouldn't let him publish it for three years, until Feynman published a paper about vortices in liquid helium, after which he said to Abrikosov, "After all, there may have been something in that idea of yours, you may publish it." So he held him back three years. But he began with this "obviously", the layer form, "obviously", so one could say — so we've got another great man who takes something for simplicity and believes that that simplicity must be right.
He used horizontal layers in his diffusion theory. The equations are much simpler.
So in his '39 paper —
He had a good reason for doing it that way, first of all.
Incidentally, Maurice Pryce told me that the first man to make a reactor design which would have worked, had it been built, was Shockley, Bill Shockley of the Bell Labs made this design, put it up to the Bell Labs management and they said, "This is too hot and big a thing for us," and they passed it up to Washington and it got lost in Washington.
Carefully put away in a drawer. But what's interesting is in '39, there were two possibilities, separation and homogeneous mixture, separation probably best in layers.
When he was faced by experimental evidence that Diebner's experiments were better, and Hoecker's theory, he wrote a review report about Diebner's experiments and mentions Hoecker's theory, says, "These experiments use a lattice of cubes in moderator. For the sake of ease of theoretical computation, we'll consider this lattice to be a homogeneous mixture," and then he goes back to his '39 paper. The point is, this wasn't very important, he didn't spend much time on it. He went to his '39 paper, repeats the calculations, comes to the conclusion that Diebner's experiments have worked out better than you would expect from a homogeneous mixture, however, there are still reasons to go ahead with the layer experiments.
I believe it, this is all totally credible to me. What people are liable to do.
I'm glad to hear that, you're the proper generation, you knew these people. I've discussed similar things with younger physicists who are utterly outraged that I intimated that so great a physicist as Heisenberg could make such a simple mistake. See, that's really the wrong way to look at it.
Right, I don't really think that, I generally think that Heisenberg was very happy when his calculations, somewhat erroneously led him to the conclusion that the bomb...I think he wanted to be a loyal German, but he also, I'm pretty sure, would not have wanted to be the creator of this devastating weapon.
No, that's fair enough.
So I think, like Hahn, Hahn had been very happy when, erroneously, he learned the capture of neutrons in U 238, that he thought, blocked the way to making an explosion, Heisenberg was probably unduly willing to accept his — but this is another one, because (crosstalk)...without affecting the bomb, the other, the nuclear reactor, the civil power reactor was their declared target.
But it's not a mistake as such, it's simply that he spent very little time on it. It wasn't his interest.
Yes, well, he was —
Both times, both papers, he was given a contract by the army to examine the theory of chain reactions, and this review that I mentioned he wrote as director of the Kaiser Wilhelm Institute of Physics. He also wrote a review article on the experiments carried out in Berlin.
One of the German scientists managed to get money out of the German Admiralty, I don't know if they told you this story, got money out of the German Admiralty for isotope separation on the grounds that if you could knock two percent off the density of iron, your battleships...(would be faster).
In 1944 Siegfried Fluegge moved from Hahn’s Institute to become professor at the University of Koenigsberg and head of the nuclear research section under the German post-office.
 Here the “Black Forest gang” refers to the German nuclear scientists whose institutes had been evacuated to the Black Forest in the last years of the war.
The Americans employed Osenberg after the war, as a prisoner of war.
Here the reference is to a seminar held by Heisenberg while interned at Farm Hall in England after the war.
Samuel Goudsmit, Alsos (Schumann: New York: 1947). Reprinted (Tomas: Los Angeles: 1983).
Heinz Barwich Das rote Atom (Scherz: 1967).