They would be able to salvage the reputation of their physics community

Thursday, June 20th, 2019

In Captain America: The First Avenger, the quasi-Nazi villain Red Skull wields a cosmic cube, and I must admit that’s what came to mind when I read about the two-inch uranium cubes at the center of Nazi Germany’s nuclear program:

Several German physicists were involved in that research program; perhaps the most widely recognized was Werner Heisenberg.

Rather than working together under central leadership the way the Manhattan Project scientists eventually would, the German nuclear researchers were divided into three groups that each ran a separate series of experiments. Each was code-named after the city in which the experiments took place: Berlin (B), Gottow (G), and Leipzig (L). Although the Germans began their work nearly two years before serious US efforts began, their progress toward creating a sustained nuclear reactor was extremely slow. The reasons for the delay were varied and complex and included fierce competition over finite resources, bitter interpersonal rivalries, and ineffectual scientific management.

In the winter of 1944, as the Allies began their invasion of Germany, the German nuclear researchers were trying desperately to build a reactor that could achieve criticality. Unaware of the immense progress the Manhattan Project had made, the Germans hoped that though they were almost certainly going to lose the war, they would be able to salvage the reputation of their physics community by being the first to achieve a self-sustaining nuclear reactor.

In holding out that hope, officials moved the Berlin reactor experiments headed by Heisenberg south ahead of the Allied invasion. They eventually landed in a cave underneath a castle, shown in figure 1, in the small town of Haigerloch in southwest Germany.

B-VIII reactor entrance at castle in Haigerloch, Germany

In that cave laboratory Heisenberg’s team built their last experiment: B-VIII, the eighth experiment of the Berlin-based group. Heisenberg described the setup of the reactor in his 1953 book Nuclear Physics. The experimental nuclear reactor comprised 664 uranium cubes, each weighing about five pounds. Aircraft cable was used to string the cubes together in long chains hanging from a lid, as shown in figure 2. The ominous uranium chandelier was submerged in a tank of heavy water surrounded by an annular wall of graphite. That configuration was the best design the German program had achieved thus far, but it was not sufficient to achieve a self-sustaining, critical reactor.

B-VIII reactor, 664 uranium cubes

In 1944, as Allied forces began moving into German-occupied territory, Leslie Groves, commander of the Manhattan Project, ordered a covert mission code-named Alsos (Greek word for “groves”) to take a small number of military personnel and scientists to the front lines in Europe to gather information on the state of the German scientific program. The mission broadly aimed to gather information and potentially capture data and instrumentation from all scientific disciplines from microscopy to aeronautics. The most pressing task was to learn how far German physicists had gotten in their study of nuclear reactions. The initial leg of the Alsos mission began in Italy and moved to Germany as the Allied military forces swept south.6 Among the men involved in the mission was Samuel Goudsmit. After the war, he went on to be the American Physical Society’s first editor-in-chief and the founder of Physical Review Letters.

As the Allies closed in on southern Germany, Heisenberg’s scientists quickly disassembled B-VIII. The uranium cubes were buried in a nearby field, the heavy water was hidden in barrels, and some of the more significant documentation was hidden in a latrine. (Goudsmit had the dubious honor of retrieving those documents.) When the Alsos team arrived in Haigerloch in late April 1945, the scientists working on the experiment were arrested and interrogated to reveal the location of the reactor materials. Heisenberg had escaped earlier by absconding east on a bicycle under cover of night with uranium cubes in his backpack.


Many scholars have long thought that the German scientists could not have possibly created a working nuclear reactor because they did not have enough uranium to make the B-VIII reactor work. In Heisenberg’s own words, “The apparatus was still a little too small to sustain a fission reaction independently, but a slight increase in its size would have been sufficient to start off the process of energy production.” That statement was recently confirmed using Monte Carlo N-particle modeling of the B-VIII reactor core. The model showed that the rough analyses completed by the Germans in 1945 were correct: The reactor core as designed would not have been able to achieve a self-sustaining nuclear chain reaction given the amount of uranium and its configuration. But the design might have worked if the Germans had put 50% more uranium cubes in the core.


  1. TRX says:

    “The reasons for the delay were varied and complex”

    Mostly, the three programs were put under three completely different branches of the government, and unlike the American or Soviet nuclear programs, each of the three had to compete for available resources, which was the problem with most Nazi weapons programs. Hitler referred to them all as “Jewish science” and was opposed to wasting effort on such balderdash, and Speer (correctly) concluded there was no way they could come up with a useable weapon before defeat, though he let the projects continue for a while anyway.

    The Japanese did their best to obliterate all evidence of their projects, but the Army, the Navy, and at least one university were working on atomic weapons. The most advanced work was done at a hydro plant in Korea, which was dismantled and relocated to the USSR after the Soviets rolled into Korea at the very end of the war.

  2. CMOT says:

    They had to use heavy water because they couldn’t get graphite moderators to work. They didn’t know it, but their graphite was contaminated with boron, a powerful neutron poison that makes it useless as a moderator. US nuke program figured that out early and was able to produce uncontaminated graphite.

    If the Nazi scientists had realized the problem with their graphite and corrected it they certainly would have got a chain reaction, and who knows what else …

  3. Graham says:

    In that movie at one point the Red Skull taunts Cap with:

    “You fool. You could have the power of the gods and instead you paint a flag on your shield and believe you fight the war of nations. I have seen the future, Captain. There are no flags.”

    And Cap replies, “Not my future.”

    Now of course this works better if you hear the first quote in Hugo Weaving’s more or less German accent from the role.

  4. Lu An Li says:

    1. Correct about the graphite. German graphite not pure enough. American graphite was.

    2. Russian troops advancing so fast on Berlin as they did with the hope to capture scientists and raw atomic research material.

    3. Germans perceived atomics not so much as a “bomb” but as a source of energy.

    4. David Irving covers all this quite well in his “Virus House”.

  5. Kirk says:

    I’ve said it before, and I’ll repeat it: I think there’s a lot we just don’t know about the German secret weapons programs.

    You look at the whole of the thing, and if you’ve got any sort of logical mind, the outward surface of things does not make any sense, at all–Unless, they had something which they thought was a workable WMD.

    You look at the resource expenditure, and any rational calculation simply cannot make sense of the whole V-2 program. Unless, they thought they had one-ton city-killers coming along shortly…

  6. Jacob G. says:

    What would 1 ton of nerve gas do to London?

  7. Kirk says:

    Kill 3,000 to 8,000 people directly, an unknown number more via secondary and tertiary effect.

    I don’t think the Germans ever designed for nerve agent dispersal with the V-2, which makes me suspect that they had other ideas. Liquids are notorious for being difficult to launch via ballistic missile–One of the things Saddam subcontracted to Gerald Bull was having him sneak computer time here in the US to do calculations related to inflight liquid dynamics with regards to SCUD missiles equipped with liquid nerve agent warheads.

    That, rather than the Babylon Gun project, was probably what got the Mossad convinced they needed to kill him, if they did.

  8. Isegoria says:

    A quick glance at Wikipedia suggests that Germany produced tons of nerve gas during World War 2 but decided against using it. This excerpt from The Crime and Punishment of I.G. Farben suggests why not:

    Speer, who was strongly opposed to the introduction of tabun, flew Otto Ambros, I.G.’s authority on poison gas as well as synthetic rubber, to the meeting. Hitler asked Ambros, “What is the other side doing about poison gas?” Ambros explained that the enemy, because of its greater access to ethylene, probably had a greater capacity to produce mustard gas than Germany did. Hitler interrupted to explain that he was not referring to traditional poison gases: “I understand that the countries with petroleum are in a position to make more [mustard gas], but Germany has a special gas, tabun. In this we have a monopoly in Germany.” He specifically wanted to know whether the enemy had access to such a gas and what it was doing in this area. To Hitler’s disappointment Ambros replied, “I have justified reasons to assume that tabun, too, is known abroad. I know that tabun was publicized as early as 1902, that Sarin was patented and that these substances appeared in patents. ” (…)Ambros was informing Hitler of an extraordinary fact about one of Germany’s most secret weapons. The essential nature of tabun and sarin had already been disclosed in the technical journals as far back as 1902 and I.G. had patented both products in 1937 and 1938. Ambros then warned Hitler that if Germany used tabun, it must face the possibility that the Allies could produce this gas in much larger quantities. Upon receiving this discouraging report, Hitler abruptly left the meeting. The nerve gases would not be used, for the time being at least, although they would continue to be produced and tested.

  9. Isegoria says:

    Project Babylon came up here years ago, for those who don’t know about the supergun project.

  10. Kirk says:

    Hitler had a notable aversion to war gases, regarding them with the justifiable distaste that a victim of them would possess.

    Plus, I don’t think that the V-2 ballistic missile would have done very well, with a liquid cargo as a warhead. It took a lot of work for the Soviets to develop a SCUD that could carry such, and it wasn’t at all easy for Saddam–I don’t think he ever really got that working, TBH. Even with Bull’s able help…

    No, if I had to wager on whatever it was they thought they had going, I’d bet on a “Dirty Bomb” sort of affair, or a dry poison. Maybe even an atomic weapon of some sort, based on a track we officially don’t know about.

    Friend of mine from the Iraq days was an NBC survey expert, and his highly unofficial claim to me was that when he’d been involved in going into Eastern Germany and Poland after the Wall came down and doing survey work, there were some very, very strange signs around areas of suspected Nazi weapons research. As in, they found radioactive decay remnants that you’d expect to find around a low-yield atomic weapon, indicating that something like that might have been tested.

    Problem was, after close to fifty years of Soviet occupation, there was no real way of attributing what those signatures meant–The official explanation was that the stuff they found came from things the Soviets had moved from their own test sites into those areas, or that the Soviets had done testing in the area themselves.

    Nobody wants to challenge the accepted version of things, but I have some issues with the “official version” of events during the aftermath of the war. I find it interesting that the Soviets glommed onto all the Japanese facilities in North Korea, and shipped them off for study and use, along with a bunch of the people who worked there. You look at the speed with which the Soviets managed to develop their weapons, and the question comes to mind, just exactly how much did they do themselves, and how much of a leg up did they get by way of looting German and Japanese facilities.

    Somewhere, years ago, I read a book that outlined this whole list of known Japanese and German physicists who were well-known and publishing before the war, and who vanished within the chaos. There was a ton of talent there, that could very well have wound up under Soviet control, and which might argue for there being a bit more to the German and Japanese programs than we’ve been told.

    You can only see the bare bones of an alternate narrative to the one we commonly accept, but there’s enough there to make one wonder.

    I mean, still… You look at the whole set of numbers on the V-1 and V-2, and you’re left incredulous. Each one of those damn rockets cost about what a B-24 did, with a proportionate impact for the entire program on the German wartime economy being larger than the US B-29 and Manhattan Project combined… All to build a one-shot delivery system for a ton of high explosives? WTF? If I were sitting in a meeting where that was outlined, I’d have done a few back-of-the-briefing-paper calculations, and raised my hand to go “Uhmmm… Guys…?”. I can’t bring myself to believe that that many Germans were so besotted with von Braun’s vision and Nazi ideology that nobody on their side did those calculations and asked those questions.

    I mean, yeah… They were all nuts, by any rational standard, but… That nuts?

  11. TRX says:

    Hitler was gassed, temporarily blinded, and spent a long and painful time in the hospital during WWI. He opposed the use of chemical weapons based on that.

    The British built up some CW stocks, but Churchill decided not to deploy them unless the Germans did so first.

    I’ve never seen anything about the reasoning on the Soviet side.

  12. Sam J. says:

    “…The Japanese did their best to obliterate all evidence of their projects, but the Army, the Navy, and at least one university were working on atomic weapons. The most advanced work was done at a hydro plant in Korea, which was dismantled and relocated to the USSR after the Soviets rolled into Korea at the very end of the war…”

    There’s a book about this: Japan’s Secret War: Japan’s Race Against Time to Build Its Own Atomic Bomb.

    According to the author he interviewed a scientist that worked on the program and he said they made one bomb which was tested successfully off the coast of North Korea a few weeks before the American bomb was dropped. Notably where NK made their nukes is the same place the Japanese were said to have done so.

  13. Sam J. says:

    “…I’ve said it before, and I’ll repeat it: I think there’s a lot we just don’t know about the German secret weapons programs…”

    I think this also. I’ve read a bunch of what could be whacky stuff about this and some not so whacky.

    There’s first person accounts of large blast the Germans did but they could have been fuel air explosives.

    The Japanese I believe very much had a nuclear program that was almost successful. The book I commented on combined with some other data. Namely the kamikaze suicide aircraft program and this aircraft carrying submarine.

    This thing cost a fortune and as far as I can see had no use but to carry nukes.

  14. CVLR says:

    Perhaps you may be interested in reading about the Demon Core.

    The experimenter needed to maintain a slight separation between the reflector halves in order to stay below criticality. The standard protocol was to use shims between the halves, as allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion. Under Slotin’s own unapproved protocol, the shims were not used and the only thing preventing the closure was the blade of a standard straight screwdriver manipulated in Slotin’s other hand. Slotin, who was given to bravado, became the local expert, performing the test on almost a dozen occasions, often in his trademark blue jeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be “dead within a year” if they continued performing the test in that manner.

  15. CVLR says:


    mean, still… You look at the whole set of numbers on the V-1 and V-2, and you’re left incredulous. Each one of those damn rockets cost about what a B-24 did, with a proportionate impact for the entire program on the German wartime economy being larger than the US B-29 and Manhattan Project combined… All to build a one-shot delivery system for a ton of high explosives? WTF?

    You make a lot of sense.

  16. Slovenian Guest says:

    Did Israel´s atomic bomb emerge from the Nazi womb:

  17. Kirk says:

    Slovenian Guest,

    Well, that connects some dots and adds some data I didn’t know.

    At this point, I think I am convinced: The Germans absolutely did have an atomic bomb program, and they were a lot closer than we’ve been told. That detail about the patents in Munich is telling; nowhere in the literature that I’ve found have I seen that bit about the patents being filed by the Germans on the Thuringia track.

    Fascinating. I wonder why they have been so careful about denial? Is it, perhaps, because the Pu track can be done a lot more easily than the enriched Uranium one, and they were working even then to make proliferation a lot harder? Have the Iranians, for example, been going down the enrichment track because of this, while the Israelis knew about the Pu track, and made use of it?

  18. Sam J. says:

    CVLR said, “Perhaps you may be interested in reading about the Demon Core.”

    I read about that somewhere. I think in one of the labs newsletters. And they eventually did get caught doing this. Not sure if it was the same person but the two halves met, there was huge flash of radiation and the guy holding them died from radiation poisoning.

    Slovenian Guest:

    Good video. I wonder if the Nazi bell written about by Nick Cook was really about some different way of making plutonium??? He says it was ant-gravity but I’m not really buying that. At the same time I do believe there is a such a thing as an Inertia drive that pushes against the inertia of the universe and expels no matter like a rocket. I just don’t see how the bell being built as reported by Cook would do that.

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