What did the Nazis know about the Manhattan Project?

by Alex Wellerstein, published September 13th, 2013

The primary motivation of much Manhattan Project secrecy was to keep the Germans from finding out that the United States and United Kingdom were feverishly working on developing nuclear weapons. So it seems a pretty sensible question to ask: Did it work? That is, did the secrecy keep the Germans from knowing about Allied progress on the bomb?

Strangely enough, I wasn’t able to find much of anything published on the question of what knowledge, if any, the Axis powers had about the atomic bomb. The fact that they didn’t develop one themselves is not strong evidence — it just might mean that such knowledge was very limited, or not believed, or not shared correctly. I can’t do the topic the justice it deserves, because I’m not conversant enough with the sources of Axis foreign intelligence, but I can present some thoughts and intriguing little discoveries on here regarding the German program. If anyone has further thoughts, or evidence, I’m all ears.

Farm Hall, the British country estate.

Farm Hall, the British country estate.

Where might we look for such evidence? The major, obvious source are the Farm Hall transcripts. Farm Hall was the British country manor where ten of Germany’s nuclear scientists were kept for six months. Their conversations were bugged. They were, on August 7th, told about the atomic bombing of Hiroshima, and the transcripts were carefully probed at the time, and many times since, for any insight given into what the German nuclear weapons program had been at the time. The transcripts are a notoriously tricky primary source, in part because the original German copies have apparently since been lost (so we only have an English translation), and because there are some indications that the scientists were aware they were being bugged. Separately there is the psychological complexity of the issue, as the scientists were trying to come to terms with themselves, an imagined German public, and an imagined world public regarding their participation (or lack thereof) in making nuclear weapons for Hitler.1

With that said, is there anything in the Farm Hall transcripts that enlightens us one way or the other? The most significant part is that the announcement of Hiroshima, first given orally, “was greeted with incredulity.” See, for example, this sort of exchange:

HEISENBERG: Did they use the word uranium in connection with this atomic bomb?

ALL: No.

HEISENBERG: Then it’s got nothing to do with atoms, but the equivalent of 20,000 tons of high explosive is terrific. […]

GERLACH: Would it be possible that they have got an engine [reactor] running fairly well, that they have had it long enough to separate “93”? [neptunium]

HAHN: I don’t believe it.

HEISENBERG: All I can suggest is that some dilettante in America who knows very little about it has bluffed them in saying: “If you drop this it has the equivalent of 20,000 tons of high explosive” and in reality doesn’t work at all. […]

WEIZSÄCKER: I don’t think it has anything to do with uranium. […]

HAHN: If they really have got it, they have been very clever in keeping it secret.2

All of which has been sometimes taken as pretty strong evidence that these guys didn’t know much about the Allied project. But a closer reading is less clear, because, among other things, not everyone is participating in this discussion. One of the many problems with the German nuclear program was a lack of coordination and a lack of shared knowledge. That Otto Hahn knew nothing of it seems entirely believable, but irrelevant, since he wasn’t really working on the nuclear program in any kind of military capacity. Werner Heisenberg and Carl Friedrich von Weizsäcker worked together so it makes sense that they would be on basically the same page. But what about the others? 

Farm Hall mugshots: Werner Heisenberg, Carl Friederich von Weiszäcker, Otto Hahn, and Kurt Diebner.

Farm Hall mugshots: Werner Heisenberg, Carl Friederich von Weiszäcker, Otto Hahn, and Kurt Diebner.

Walter Gerlach was in a more administrative role, so one might imagine he would know of any foreign intelligence on the subject. He speaks very little in this part of the transcript, only the question about reactors, and he is not one of the outright initial doubters. Asking whether they could have had reactors does not indicate that he was unaware of an Allied bomb project in general, especially given the compartmentalization of the Manhattan Project. He does, much later in the transcript, apparently express private surprise with Heisenberg that “they had known nothing about the preparations that had been made in America,” though. And what of Kurt Diebner? Diebner ran the other major research wing of the German nuclear program, separate from Heisenberg. He says almost nothing in this section of the transcript, only noting that “there is also a photochemical process” for enriching uranium. Again, this tells us nothing about what he knew.3

Probing the transcript further, we find a few other odd exchanges:

HAHN: From the many scientific things which my two American collaborators sent me up to 1940, I could see that the Americans were interested in the business. 

WEIZSÄCKER: In 1940 van der Grinten wrote me, saying he was separating isotopes with General Electric.

HARTECK: Was van der Grinten a good man?

WEIZSÄCKER: He wasn’t really very good but the fact that he was being used showed that they were working on it.4

I read these as Hahn and Weizsäcker trying to recall whether they had any indication of Allied interest. Considering their only memories are from 1940 (before the Manhattan Project really began), they are actually a good indication that they did not have any truly specific intelligence.

Heisenberg three times tells a story about being contacted from someone in the German Foreign Office about uranium questions:

HEISENBERG: About a year ago, I heard from Segner [probably Sethke] from the Foreign Office that the Americans had threatened to drop a uranium bomb on Dresden if we didn’t surrender soon. At the time I was asked whether I thought it possible, and, with complete conviction, I replied: “No.”5

Now that is a strange story. I have no idea what this Sethke would have been referring to — some strange rumor. Whether it is just nonsense, or based on some actual intelligence, it’s impossible to know from just this snippet. Later, when Heisenberg tells another version of the story (this time making his answer that it was “absolutely possible”), he specifies it was in July 1944 and that it was “a senior SS official” who had asked him about the bomb.6

More Farm Hall mugshots: Walter Gerlach, Paul Harteck, Max von Laue, Karl Wirtz.

More Farm Hall mugshots: Walter Gerlach, Paul Harteck, Max von Laue, Karl Wirtz.

There is also one small exchange before the German scientists were told about Hiroshima. On August 4th, Heisenberg, Gerlach, and Hahn had this exchange:

GERLACH: The [British] Major [Rittner] asked me what we had known about scientific work in enemy countries, especially on uranium. I said, “Absolutely nothing. All the information we got was absurd.”

HEISENBERG: In that respect one should never mention any names even if one knew of a German who had anything to do with it.

GERLACH: For instance, I never mentioned the name of that man Albers (?). The “Secret Service” people kept asking me: “From whom did you get information?” and I always replied: “There was an official in Speer’s ministry and in the Air Ministry who gave it out officially.” I did not say it was Albers (?) who did it.

HEISENBERG: I had a special man who sent me amazing information from Switzerland. That was some special office. Of course I have burnt all the correspondence and I have forgotten his name.

HAHN: Did you actually get any new information from him?

HEISENBERG: At that time I always knew exactly what was being discussed in the Scherrer Institute regarding uranium. Apparently he was often there when Scherrer lectured and knew what they were talking about. It was nothing very exciting but, for instance, he once reported that the Americans had just built a new heavy water plant and that sort of thing.7

And there it ends. Other than the mention of heavy water, it is too vague to make much sense of. (The Manhattan Project built several heavy water plants are part of what they called the P-9 Project, as part of their “leave no stone unturned” approach. They upgraded an existing ammonia plant at Trail, British Columbia to produce heavy water, and built three supplementary facilities at military sites in West Virginia, Indiana, and Alabama.)

After the scientists had heard the official BBC radio announcement, they all began to believe it was true, and worked out fairly quickly how it probably would have worked (though even there, they were still impressively confused at times) and famously hashed over why they didn’t get one made. No further invocations of foreign information or intelligence were made that I found.8

My overall impression is that for the bulk of the ten scientists, the Allied atomic bomb probably did come as a genuine surprise of immense magnitude. But there are enough hints there to suggest that various bits and pieces were out there amongst their foreign intelligence officials, whether they shared all of that with the scientists or not. And as we’ve see in the Soviet case, just because the spies know something doesn’t mean it percolates back to the scientists working on it — the use of foreign intelligence is not a straightforward operation. And there are several scientists whose reactions were not individually recorded (e.g. Diebner). Of the scientists who talked a lot, they seemed genuinely clueless about what the Americans had done, but not all of them talked.

Are there any other indications? One thing that one finds on the Internet are assertions that the last attempt by the Nazis to deposit saboteurs on American soil, Operation Elster (Magpie), was supposedly aimed at sabotaging the Manhattan Project. Like all such Nazi efforts, the saboteurs in question were rounded up pretty quickly. Were they really targeting the Manhattan Project? I suspect not. The sources that give such information all seem to trace back to a postwar memoir of one of those captured. David Kahn has written that he thinks it is nonsense; I am inclined to agree.9) The idea that a single pair of spies would be sent to gain information on, much less sabotage, the Manhattan Project is too silly to be believed without corroborating evidence.

J. Edgar Hoover, 1941. Source.

J. Edgar Hoover, 1941. Source.

But there is one last interesting source that I stumbled across. In early February 1945, J. Edgar Hoover wrote a memo to Harry Hopkins (one of Roosevelt’s closest aides) explaining that the FBI had information that indicated German interest in atomic matters. Specifically, Hoover wrote:

As you are well aware, the Army for the past two years has been vitally interested in a highly secret project for the development of an atomic explosive. […]

Recently, in connection with the operation of a radio station by a German agent under control of the Federal Bureau of Investigation but which station the Germans believe to be a free station, an inquiry was received from Germany containing the following questions regarding the status of atomic explosive experimentation in the United States:

First, where is the heavy water being produced? In what quantities? What method? Who are users?

Second, in what Laboratories is work being carried on with large quantities of uranium? Did accidents happen there? What does protection against Neutronic Rays consist of in these laboratories? What is the material and the strength of coating?

Third, is anything known concerning the production of bodies or molecules out of metallic uranium rods, tubes, plates? Are these bodies provided with coverings for protection? Of what do these coverings consist?10

Now this looks like a legitimate technical intelligence inquiry. These are very specific questions regarding reactor construction. Not necessarily bomb construction, mind you. But it does look like someone working on reactors passed some questions up the chain of command. (The fact, incidentally, that this came to the FBI from a double-agent is also telling — the German foreign intelligence networks were notoriously compromised, yet another reason they missed so much.)

The questions reveal, though, that whomever asked them did not realize that the Americans had already been building massive, industrial-sized, carbon-moderated (not heavy water!) nuclear reactors in Hanford, Washington. Note the lack of any queries regarding uranium enrichment. Note that the questions are narrowly technical, the kind of questions you would ask if you are trying to build your own reactor, not ferret out a clandestine bomb program.

That the Germans were asking such basic, ignorant questions so late in the game — the Red Army was bearing down on Berlin and their atomic program, like so many other things, was in a tizzy11is perhaps the greatest indication that they knew very little about the American Manhattan Project indeed. That they were asking questions at all is not surprising, but the lateness perhaps is. The Soviet physicist Georgii Flerov figured out that the Americans must be working on a nuclear program in 1942, when he noticed that nobody was publishing on the subject — specifically, that nobody was citing his publication on the spontaneous fission of uranium-238. One wonders why the Germans were less observant of this fact, especially given the amount of “brain drain” their own institutes suffered.12 They also appear to have missed or misunderstood all of the various leaks, accidental disclosures, and other signs that drove General Groves and others involved with Manhattan Project security so mad. Many pieces were there for them to put together, but they didn’t solve the puzzle.13

Allied troops disassembling the German experimental research reactor at Haigerloch.

Allied troops disassembling the German experimental research reactor at Haigerloch as part of Alsos.

Lastly, we have the take of Samuel Goudsmit, the head of the Alsos expedition. In an unpublished memorandum written in late 1945, claimed that the Alsos investigation into the German work had shown that “the enemy was equally ignorant of Allied scientific and technical work,” though notes that in 1939, a team of three Germans were sent to the USA to learn about American interest in uranium research. (This was well before there was much American interest in such.) As he was prone to do, Goudsmit generalized greatly from this, assuming that scientific and technical intelligence was too difficult to pick up during that war. The Soviets, as always, proved an important exception to Goudsmit’s generalizations.14 In any case, though, this does indicate that there aren’t probably an exciting espionage gems hiding in the Alsos records.

Wrapping everything up, my basic conclusion is that if German intelligence had an inkling about the American atomic bomb program, they didn’t develop the idea and they didn’t communicate it to several of their top scientists on the program. Heisenberg seems genuinely foolish on the entire subject. Diebner’s lack of participation makes it hard to gauge his knowledge, but it strikes me as strange (though not impossible) that he would know of such things but Heisenberg would be ignorant of them. Entirely separate is the question of who asked the SS to investigate what the Americans were doing with heavy water — but the queries there demonstrate that whomever is asking knows almost nothing about the Allied program, and may in fact be trying to find out how to improve their own reactor work.

A consistent theme in the Farm Hall transcripts and the Alsos investigation is that the Germans seem to have honestly thought that their work on the “uranium problem” was well beyond what anyone else might have been doing, and that the Allies would be desperate to “buy” their reactor research in the postwar. They apparently were not motivated to check to see whether this arrogance was founded, and part of the depression and desperation one sees them going through after Hiroshima and Nagasaki is a remark on their perception of irrelevance. As Otto Hahn chided them right after they learned of Hiroshima: “If the Americans have a uranium bomb then you’re all second raters.”

  1. The best copy of the transcripts is Jeremy Bernstein’s heavily annotated version, Hitler’s Uranium Club: The Secret Recordings at Farm Hall, Second Edition (New York: Copernicus Books, 2001). My quotations and citations refer to this specific version. []
  2. Bernstein, 116-117. []
  3. Photochemical processes for enriching uranium were investigated during the Manhattan Project, but not seriously pursued. []
  4. Bernstein, 119. []
  5. Bernstein, 124. []
  6. Bernstein, 139. []
  7. Bernstein, 108. Note that the (?)’s are in the original transcript. []
  8. There is one small bit about talking about thorium with an (Indian) Japanese spy, but it seems unrelated to the bomb question directly, and the spy in question doesn’t seem to have known anything. []
  9. David Kahn writes in Hitler’s Spies: German Military Intelligence in World War II, “[Erich] Gimpel’s [one of the spies] ghostwritten book, Spy for Germany, must be used with the greatest caution, as it differs in a number of critical points from his statement [to the FBI]. The most important are the book’s claims that he was assigned to ferret out atomic secrets, that he succeeded to some extent, and that he radioed a message to Germany. None of these are supported by his statement or by Colepaugh’s [a collaborator] or by postwar interrogations of his spymasters, and the atomic claim is specifically contradicted by a statement of Schellenberg’s [a top Nazi spy].” There just doesn’t seem to be any hard evidence behind the assertion that Elster had something to do with the Manhattan Project. Gimpel’s books provide zero believable details about the matter — he reports that he was just supposed to figure out what was going on (no list of targets, names, theories, etc. []
  10. J. Edgar Hoover to Harry Hopkins (9 February 1945), in Harrison-Bundy Files Relating to the Development of the Atomic Bomb, 1942-1946, microfilm publication M1108 (Washington, D.C.: National Archives and Records Administration, 1980), Folder 62: “Security (Manhattan Project),” Roll 4, Target 8. []
  11. See Samuel Goudsmit, Alsos (Tomash, 1983 [1946]), 183-185. []
  12. At one point in the Farm Hall transcripts, it is noted that “Hahn remarked on the fact that there had been no publication of work on uranium fission in British or American scientific journals since January 1940, but he thought there had been one published in Russia on the spontaneous fission of uranium with deuterons.” So, at least retrospectively, Hahn realizes that there was this silence, with the exception of Flerov (probably the Russian he is thinking about). []
  13. Goudsmit describes a conversation between Paul Rosbaud and Walther Gerlach in February 1945 in which Rosbaud asks Gerlach, “Have you considered that the American, British, or Russian scientists know as much or perhaps more about it than you do?” If this actually occurred, one wonders if Gerlach didn’t follow up on the issue, ergo the spy query. But this is just supposition. On the conversation, see Goudsmit, Alsos, 185. In any case, the whole conversation, if true, is further evidence of Gerlach’s ignorance at that point — he was still under the delusion that the Allies would have something to gain from the German work on heavy water. []
  14. Samuel Goudsmit to C.P. Nichols, “Scientific Intelligence” (26 November 1945), Goudsmit papers. []

32 Responses to “What did the Nazis know about the Manhattan Project?”

  1. You might also like this one: translation and discussion of a Japanese documentary about what the Japanese knew in the early summer of 1945 about the American work on the atom bomb:

    • That’s interesting. I wish the original sources were available. There is somewhat of a disconnect in the argument. I am curious what their 1943 intelligence was, and how by 1945 they had concluded that the US wasn’t enriching uranium. Them noticing the odd behavior of the 509th, though, is interesting indeed. But I’m mostly interested in the question of what fed into their 1943 and 1945 assessments.

  2. Stan Norris says:


    Not sure if this was part of Operation Elster (Magpie) or not. Would like to know more about that. This is what I said in Racing for the Bomb, page 267.

    “In one instance Groves framed a message of disinformation to deceive the Germans. It came about when some German agents, who had come through Portugal, were apprehended as soon as they arrived in United States. Groves was told of this German espionage attempt at the Military Policy Committee meeting of June 21, 1944. He deliberated with his security people over what to do. They wanted to use the agents to send the message back to Berlin that nothing was being done on atomic energy in the United States. Groves overruled them, and a message was crafted saying that certain people at certain universities were doing certain work. Obviously, those who were mentioned had nothing to do with the project. Groves’s reasoning was that by acknowledging a minimal effort, rather than none at all, it would more likely convince the Germans that nothing could from such a small academic program. In one instance Groves framed a message of disinformation to deceive the Germans. It came about when some German agents, who had come through Portugal, were apprehended as soon as they arrived in United States. Groves was told of this German espionage attempt at the Military Policy Committee meeting of June 21, 1944. He deliberated with his security people over what to do. They wanted to use the agents to send the message back to Berlin that nothing was being done on atomic energy in the United States. Groves overruled them, and a message was crafted saying that certain people at certain universities were doing certain work. Obviously, those who were mentioned had nothing to do with the project. Groves’s reasoning was that by acknowledging a minimal effort, rather than none at all, it would more likely convince the Germans that nothing could from such a small academic program.”

    • That’s fascinating! I will follow up on this… it’s interesting that he claimed that unimportant people were working on it. If the Germans had better technical coordination you’d expect them to say, “wait… so where’s Fermi in all this?”

      • Tony G. says:

        I find it interesting that the Soviet physicist Flerov figured the Americans must be working on a nuclear program because, basically, there was an absence of public academic information and/or interest on their part. However, according to Stan Norris’ insight, Groves evidently realized this same fact could be enough of a security issue to warrant passing disinformation to the Germans through the compromised agents. What strikes me as odd is the reasoning of the apparent half-hearted attempt to disinform. Rather than trying to convince the Germans that there was no reasonable expectation of an American nuclear program based upon the “nuclear disassociated” names and universities, would it not make as much or more sense to pass that “obviously lacking known names” (Fermi, as you pointed out, for instance) information along as bait to see the nature of return inquiries? It seems odd to me that the infamous Groves security apparatus would handle this opportunity as open and shut as his “reasoning” suggests. I’m interested in any follow up you can muster on this subject. Good find by Stan Norris.

        • All of the efforts at disinformation (there were a few of them) were pretty half-hearted. Groves seems to have been of the philosophy that disinformation was arguably more dangerous than just silence. Telling lies is trickier than saying nothing, in a sense, because lies can be specifically investigated, whereas silence still leaves a very broad target.

  3. Ben Johnson says:

    If the Germans knew nothing of our atomic program they knew ‘something’ of Japan’s, right? I seem to remember a story of the Germans sending some Uranium on a U-Boat to Japan. Were the Japanese any farther along than the Germans?

    • The Germans did send some uranium to Japan, but to my knowledge its purpose has never been fully sussed out. There are non-nuclear things you can do with natural uranium metal, as well. In any case, it was only 560 kg of uranium oxide — not enough to make a difference with anything. (CP-1 had something like +2,000 kg of uranium oxide in it, I believe.) The Japanese were definitely not further along than the Germans. The Germans almost had an experimental reactor going by 1945; the Japanese were not even close to that sort of thing. They never had enough uranium on hand to do anything interesting with.

      • Stan Norris says:

        There is a book by Carter Hydrick that dives into the controversy of whether the uranium aboard a captured German submarine ended up in Little Boy. I refuted this myth, making the following points.

        Carter Hydrick argues in his book Critical Mass: How Nazi Germany Surrendered Enriched Uranium for the United States’ Atomic Bomb that the 1,200 pounds of uranium carried aboard German submarine U-234 bound for Japan was enriched and ended up in the Little Boy bomb that was dropped on Hiroshima. While it makes for a good story it has little to do with the facts. Mr. Hydrick displays a fundamental misunderstanding of the physics, chemistry, and metallurgy of uranium, to say nothing of how the actual HEU produced at Oak Ridge ended up in the Little Boy bomb.

        1. There is no evidence that Germany enriched uranium to any significant degree. The uranium that was aboard submarine U-234 was uranium oxide, un-enriched ore. Some have speculated that perhaps this ore went to Oak Ridge and went through the processing steps at S-50, K-25 and Y-12 to turn it into HEU. To what percentage U-235 was the German uranium enriched to?

        2. Mr. Hydrick claims that in mid-April 1945 the scientists realized that they needed three times more HEU than they originally determined and that the German uranium helped ease the crisis. I am not sure what Hydrick is referring to in mid-April 1945 but whatever it is it is not how the quantity of HEU was determined. In August 1944 James Conant visited Los Alamos and reported to Groves on the findings of his trip. He tells Groves that the latest value for a critical size of U-235, which he termed a “crit,” was 13 kg plus or minus 2 kg. A “crit” was defined “as the critical size for a fast neutron chain in the most favorable tamper.” (Emphasis in original). Conant goes on to say that the gun type bomb “seems well in hand” and that, “Present estimates are that for 10,000 – 20,000 tons TNT equivalent 3-4 crits of “25” [U-235] will be required. This means 39-60 kilos of “25” (as effective product). Less than 3 crits, it is predicted will give very much less than 10,000 tons equivalent, the energy falling off rapidly as the amount is lowered below 3 crits.”

        With S-50. Y-12 and K-25 all in operation Groves had a good idea of when there would be enough. We have a precise record of the batches of HEU that were processed at Oak Ridge

        3. It is totally outlandish to claim that without the German uranium we would not have had the Hiroshima bomb and the Nagasaki bomb ready when they were, and that probably we would not have had a bomb of our own until late 1945 or early 1946. Not if General Groves had anything to say about it. And he had plenty to say about it and knew the schedules.

        4. There would seem to be definitive proof that the material from the German submarine was not used. General Groves’ Appointment Book lists a 10:35 am phone call on August 13, 1945. The notation says, “Admiral Hussey called Gen. Groves re: Admiral Edwards just called asking if the material we got from the German submarine was of any use to the program. General advised it wasn’t of any help yet but it will be utilized.”
        Case closed

        • Good points, Stan. Was it ore or oxide? I had assumed the latter. (Ore, of course, is unprocessed, straight-from-the-ground stuff, and only a small percent of it is actually even uranium. Oxide is just concentrated uranium from the ore with all of the other stuff, like vanadium, stripped out. E.g. yellowcake.)

          I have seen some evidence that some amount of recovered German uranium made it into the general feed, but not that this particular uranium had been. The Manhattan Project History says:

          “The Washington Office also obtained approximately 481 tons of U3O8 in the form of miscellaneous compounds, mostly impure sodium salts. These materials were found by our armed forces in the European Theatre of Operations.”

          Which is the only unusual source of uranium mentioned in the history. From the context I presume it was put into the production feed for Oak Ridge, mingled with the rest. A trickier question is what they did with the solid U metal they found at the German research sites. One cube of it, I have been told, ended up at Harvard. They had a cube of U metal in a lead envelope when I was a student there, which they would sometimes loan to me for classroom demonstration purposes, and this was supposedly its origin, though I have seen no documentation to prove it.

          Anyway, I completely agree that the Hydrick book is just baseless sensationalism. There is so much of it out there.

          • Bruce Hunt says:

            Weighing in very late on this, but I think you’ll find that the uranium compounds the Germans were trying to send to the Japanese were meant to be used as catalysts in making synthetic fuel — that is, they were to be used for their chemical properties rather than anything involving fission or nuclear physics. Anthony Stranges of Texas A&M has written on the history of the German synthetic fuel program and has confirmed to me that uranium compounds were among those they used as catalysts. Such synthetic fuel would, of course, have been of immense interest to the Japanese, who were running very low on motor fuel by 1945.

            And yes, the Hydrick book is wrong about nearly everything..

  4. Jonas Persson says:

    I don’t remember which German ministry that was running the Vemork heavy water facility in Norway during the war. That might be a clue, as heavy water was of major interest for the Germans.
    I do not think the scientists got any or just very little information, so the Farm Hall transcripts is not a particular good source.

  5. Tom Powers says:

    German intelligence files from the war tell us little about German efforts to monitor Allied bomb development because there were no efforts to record. Werner Heisenberg and other German scientists who worked on “uranium research” during the war made no effort to alert German intelligence to the possible danger posed by an Allied atomic bomb, and made no effort to convince Albert Speer, in charge of the German wartime economy, that development of a bomb ought to be a high priority. As a result, Speer quit paying attention to the research project in 1942 and no serious effort at development was ever mounted by the Germans. Whether German intelligence, if warned, could have penetrated the Manhattan Project as the Russians did is unlikely, but it never occurred to them to try. Nor did the Germans succeed in penetrating Russian intelligence, which might have told them what Heisenberg and others did not.

    American fears of the Germans were the direct result of untiring efforts before American entry into the war by refugee scientists, Leo Szilard among others, to warn high American officials of the danger and to insist that something had to be done. Heisenberg and others could have followed the same course but did not. They told Speer and other officials that a bomb, while theoretically possible, would be too big, too expensive and too uncertain of success for Germany to undertake in wartime.

    The British, on the other hand, had a pretty good understanding of the status of German research obtained through their agent Paul Rosbaud, a scientific publisher in Berlin, and through contacts in the Norwegian underground who participated in the effort to destroy the heavy water plant at Vermork. The Germans should have inferred from the repeated Allied efforts to destroy the plant that the Allies feared a German bomb, and were themselves, as a result, almost certainly trying to build one, too. But German intelligence never made this connection. The British told General Groves, who was running the Manhattan Project, that no German bomb was likely but they declined to share the details of how they knew this to be true. Groves, suspicious, mounted his own effort through Major Robert Furman of his office and the OSS, which put several officers under Grove’s effective control. These efforts were relentless and included attempts to kidnap or assassinate Heisenberg and to target scientists personally in bombing raids. At the end of the war the focus of the effort was shifted to detention of Heisenberg and led directly to the incarceration of German scientists at Farm Hall. Furman, the OSS and Samuel Goudsmit of the Alsos mission established in detail just how small and hesitant the German research effort had been. Why the Germans had achieved so little was not a question that much interested Groves and other Allied officials. The story is complex and remains contentious ground.

    You can find quite a lot of additional information on this subject in my book Heisenberg’s War: The Secret History of the German Bomb (Knopf, 1993).

  6. Gomer Pyle says:

    Isn’t it possible that the German scientists were intentionally dragging their collective feet to prevent a known madman a.k.a. Hitler from obtaining that kind of power?

    • There has been a long historical argument about this. Most historians today have concluded that there is little evidence that the scientists intentionally sabotaged or slowed the project on account of politics.

  7. phuzz says:

    If you think that you are the Master Race, you tend to underestimate everybody else.

    • Peter Solem says:

      There are two points of interest, I think:

      1. Did the German scientists involved in the German nuclear effort ever understand what was laid out in the Frisch–Peierls memorandum? The whole text of that is available via Stanford University: Or did they believe that such a weapon could only be delivered by ship, and would require tons, not kilograms, of uranium? See this direct quote from that document, on the issue of what the Germans knew:

      “Information that could be helpful in this respect would be data about the exploitation of the uranium mines under German control (mainly in Czechoslovakia) and about any recent German purchases of uranium abroad. It is likely that the plant would be controlled by Dr. K. Clusius (Professor of Physical Chemistry in Munich University), the inventor of the best method for separating isotopes, and therefore information as to his whereabouts and status might also give an important clue. At the same time it is quite possible that nobody in Germany has yet realized that the separation of the uranium isotopes would make the construction of a suner-bomb nossible. Hence it is of extreme importance to keep this report secret since any rumour about the connection between uranium separation and a super-bomb may set a German scientist thinking along the right lines.”

      2. Did the Germans have any idea that plutonium existed or could be used to sustain a nuclear chain reaction? The answer there seems to be no. Seaborg’s discovery was perhaps more important than the discovery that the isotope U235 could sustain a chain reaction, with respect to weapons production – and note that all extant nuclear weapons programs today rely primarily on plutonium production.

      • My understanding is that on point 1, Heisenberg certainly was confused as to the critical mass issue even well into Farm Hall. He kept falling back onto estimates like “a ton.” I don’t know about Diebner, the other guy who might have mattered. They did know about using Clusius tubes as a means of enrichment. On point 2, though, they were aware that plutonium (obviously not by name) would be generated in reactors and could be used in bombs. Von Weizsäcker wrote a report on this in 1940. But I’m not sure they knew how much you would need in any case. Weirdly in the Farm Hall transcripts they talk about using reactor-bred neptunium, not plutonium, first. Which shows, again, that they were somewhat confused.

        The impression one gets from the Farm Hall transcripts is two-fold: one, that they knew more than they realized they knew, because they hadn’t really put it all together correctly and weren’t communicating well; and two (relatedly), they were really a sub-par bunch when compared to what the Allies had. Which is not to say that a few of them were not world-class — a few of them were. But, as Jeremy Bernstein points out, could you imagine a similar group of a dozen “top luminaries” from the Allied side (e.g. Oppenheimer, Fermi, Bethe, Lawrence, Von Neumann, Teller, Feynman, etc.) being similarly as confused about things if the situation was reversed? It is hard to picture. The number of extraordinarily superb people on the Allied side vastly outnumbered those on the German side, and we know that each of the previously-named people did make important, individual contributions to the Allies being able to pull the thing off. This isn’t to say that you need people of that calibre to pull it off, but it makes the wartime outcomes a lot less surprising.

        • µ says:

          I feel the need to make some remarks here. Firstly it is important to mention that some of the german scientist in farm hall were strongly opposing the nazi regime. Hahn, Sommerfeld and von Laue were part of the elder generation of german scientists, the ones that tought Heissenberg and von Weiszäcker, who had to watch the developments in germany from the early 1930ies on with grieve and I believe they worried about the rise of the Deutsche Physik, when mad and less capable men like Stark and Lenard rose to power and when it was forbidden to teach Relativity Theory or Quantum Mechanics at Universities. They were not jewish but they saw firsthand how their jewish colleges and students were forced out of the Academic Community. In what is now known as the great purge of 1933, a total of 72 scientist and intellectuals lost their academic titles for racist or political reasons, among them Max Born, Victor Goldschmidt, James Franck, Eugene Wigner, Leó Szilárd, Edward Teller, Fritz Haber, Emmy Noether, and Richard Courant.
          You are right when you say that the Allied outnumbered the Nazis when it comes to capable scientist on their side during the war, but if you consider the amount of capable scientists f.e. in 1930-1933 Germany was the one of the places to be. Have a look at the faculty of Goettingen before WWII. Fermi and Oppenheimer were there to study under Born, Leó Szilárd studied under Max von Laue. Sommerfeld, praised as teacher by Einstein, was in Munich his students were Heisenberg, Pauly, DeBeye and Peierls among others. Heisenberg later became doctoral advisor for Teller(in Goettingen) and Peierls(in Zurich).
          Anyway, my point is that when it comes to german ideology the generation of Hahn, Sommerfeld and von Laue was rooted in the Weimar Republic and was opposing antisemitism and against Hitler.
          You might find some answers in the correspondence of the people concerned.
          I recommend: for further reading. you can see the contents in the link,

  8. Bradley Laing says:

    —This is speculation, but here goes. I know that some national magazines, in the United States, during WW II, with no knowledge of the Manhattan Project argued that the US should start a nuclear program. I also read that in the 1960s, there was tendency for people recruited by US Intelligence to read newspapers, and then tell their US Intelligence contact that someone “in the know” had told them the real truth about A,B, or C, which in reality was just copying some thoughtful newspaper commentary and attributing it to a non-existent source.

    —How about: unreliable Neutral Country Citizen 123, with German connections, read some the US magazines, and drew up some thoughtful speculations about US science research?

    —-Then passed them onto his / her German connection, who wrote up a list of inquiries for later use?

    • There were plenty of public source “pieces” to put together; what’s interesting is that there isn’t a whole lot of evidence that they tried to find them. Groves et al. were completely unhappy with any press coverage whatsoever and assumed that all of it ended up in the hands of Axis spies, but, if so, there isn’t really any evidence of that.

  9. Bradley Laing says:

    —Question: if someone in the US had given someone in Nazi Germany the straight scoop about the Manhattan Project in 1944, and the receiving person realized that the sender’s information would not change the course of the war…

    —Wouldn’t the best thing be to burn the report, and send a phoney letter back to the sender saying “Hitler Was really Grateful! See you in Berlin for the celebration dinner in one year!” And then burn your own copy of the phoney letter, replacing it with a banality like “received package of technical information 6.10.44. Needed further analysis.”

    —Nobody further up the chain of command needed to know, right?

  10. […] the Axis powers notice this? If they did, they don’t seem to have done much with it. Which highlights an important aspect of Manhattan Project secrecy, in a way: how lucky it was. […]

  11. […] come across regarding the Nazis and the atomic bomb is the one that the German physicist Werner Heisenberg told at Farm Hall about being asked about an apparent rumor that the United States was planning to use an atomic bomb […]

  12. Martin Page says:

    Much has been written and will be written about Heisenberg’s miss-calculation. The calculation that yields 10 tons is too simplistic and pat to be taken seriously, unless you want a group of military general to understand. A detailed examination of his Farm Hall lecture has no comparison with the previous one. Setting Sin x/x to yield ‘pie’ was a mistake many made and overestimated the critical mass. He realized that the diffusion theory was not applicable when the critical radius is only 3 times the diffusion length and created a solution to over come this. Putting modern value into his equation and comparing the results with those of the Godiva experiments show he was spot on. So was his estimate of the 2nd criticality expansion, temperature, pressure, time scale and size of the X-ray fire ball.
    If having estimated a critical mass of 10 tons and the then perceived impossibility of separating 10 tons U235, why did he want to talk with Bohr about an atomic bomb unless he knew otherwise.

  13. Martin Page says:

    Some thoughts on the Farm Hall transcripts.

    Heisenberg: If I have pure 235 each neutron will immediately beget two children and than there must be a chain reaction which goes quickly.
    One neutron always makes two others in pure 235. That is to say that in order to make 10^24 neutrons I need 80 reactions one after the other. Therefore I need 80 collisions and the mean free path is about 6 centimetres. In order to make 80 collisions, I must have a lump of a radius of about 54 centimetres and that would be about a ton. ( P 84 )

    With the density of uranium ( P 134. mass 16 Kg, radius 6.2 cm ), equal to 16.0 gm/cm3 , 10^24 neutrons at 2 neutrons per collision is a mass of 195 grams.
    The ‘handy formula ‘ ( P126 ) gives the fission MFP ( weglaenge fuer spaltung ) as 22 cm but 6 cm is the diffusion length ( diffusionslaege ).
    The mean free path is about 6 cm ( weglaengen in der gegend von 6 cm ).
    At a radius of 54 cm and 16 gm/cm3, this has a mass of 10.5 tons and further the log n 10^24 / log n 2 is 79.72, which is understandably rounded to 80.

    The original germen text does not exist but it would be unlikely that the translator would confuse fission length or diffusion length with MFP. The mass of 195 gm is a very odd value to use and the impression is that there is an attempt to remember a lecture given some time ago.
    I would therefore make the supposition that the original mass of uranium was 1 Kg equal to 2.56×10^24 atoms that under go fission, then log n of this divided by log n of 2 gives 81 for which the square root is obvious. If the fission MFP of 22cm had been used then the mass would have been 520 tons, an unbelievable value compared with 10 tons.
    A well thought out simple pat estimate of the critical mass. A bluff that that has lasted over 50 years.

  14. […] are still areas of uncertainty with regards to these programs. I have written on here in the past on a few of the questions I’ve stumbled into with regards to the German program, for example. We […]

  15. Dr. Know says:

    The discussions are very interesting. However, how would one explain the discovery of depleted uranium metal ingots with swastikas found during the cleanup of a former defense facility. The nazis were enriching uranium, maybe crude, but some was produced. I do know that Stalin was upset with the US for bombing nuclear facilities in the east to prevent or delay soviet efforts. Interesting to say the least.

    • “depleted uranium metal ingots with swastikas” — sounds like nonsense. Got a reliable citation?

      The Germans did enrich extremely small amounts of uranium to extremely low amounts of enrichment, as part of their small-scale investigation into enrichment procedures. None of it was of any serious significance because they did not scale the process up.

      The US did indeed bomb German facilities that they thought had a connection to the German nuclear program (like the Auer plant that smelted uranium metal), and they did try to deny the Soviets access to German personnel and equipment that might help their own program. But this is not evidence of German advancement, just of US interest in denying the Soviets anything that might be helpful to them. The US was mostly concerned about the Soviets acquiring German uranium stockpiles, because the Soviets were known to be uranium-poor, and it takes a lot of uranium to run a real weapons project, so they’d need every scrap they could get.