How Close Did the Nazis Actually Come to Building an Atomic Bomb?

On August 6, 1945, the American B-29 bomber Enola Gay flew over the Japanese city of Hiroshima and dropped a single, 4,000 kilogram uranium bomb called Little Boy. Seconds later the bomb detonated with the equivalent power of 15 thousand tons of TNT, destroying 8 square kilometres of the city and killing an estimated 90-140,000 people. Three days later the  B-29 Bock’s Car dropped the 5,000 kg Fat Man plutonium bomb on the city of Nagasaki, killing a further 39-80,000. The age of nuclear weapons, which would cast its shadow over the following century and beyond, had begun. But while the first atomic bombs have become inextricably linked with the war in the Pacific, they were initially intended for use not against Japan, but rather Germany. From its inception, the vast scientific and industrial undertaking known as the Manhattan Project was built around fear – fear that Nazi Germany would be the first to develop an atomic bomb, placing in the hands of Adolf Hitler the ultimate weapon of terror and mass destruction. But how close were the Germans to actually developing the bomb, and is it possible that the Second World War could have ended very, very differently?

The Allies had good reason to fear that Germany was far ahead in the race to build an atomic bomb. After all, over the course of the war German scientists would produce some of the most advanced weapons the world had ever seen, including the first jet fighters and ballistic missiles. It was also German scientists who first discovered the principle of nuclear fission. In December 1938, chemists Otto Hahn and Fritz Strassman bombarded a sample of Uranium with neutron particles, generating atoms of the much lighter element Barium. Suspecting that the neutrons had split or “fissioned” the Uranium nuclei into smaller pieces, Hahn contacted his former colleague Lise Meitner, who, as a Jew, had fled Germany for Sweden. Meitner, along with her nephew Otto Frisch, soon developed a theoretical explanation for fission and, in January 1939, conducted experiments confirming Hahn and Strassman’s results. Hahn and Strassman, however, had already submitted their findings to the scientific journal Naturwissenschaften.

The implications of this discovery were immediately obvious, and in April 1939 a secret meeting of German scientists was convened in Berlin to discuss the possible applications of nuclear energy. During this meeting the possibility was raised of building an atomic bomb, prompting chemist Paul Harteck wrote a memo to German War Office or Reichswehr stating that:

“…an explosive many orders of magnitude more powerful than the conventional ones [could give] that country which first makes use of it an unsurpassable advantage.” 

 The theoretical feasibility of such a weapon was further confirmed by physicist Hans Geiger, and the Reichswehr agreed to fund a formal nuclear research program. On September 1, 1939, the Second World War erupted as German forces stormed into Poland. At the end of that month a second meeting of scientists was convened by physicist Kurt Debner, attended by such luminaries as Abraham Esau, Walter Gerlach, Erich Schumann, Walter Bothe, Klaus Clusius, and Nobel laureate Werner Heisenberg – the most famous scientist in Germany at the time. By the end of the meeting the attendees agreed to focus their efforts on three main goals essential to the development of an atomic bomb: the construction of a functioning nuclear reactor or “uranium machine,” the separation of Uranium isotopes, and research into fast neutron fission. While officially designated the Uranprojekt or “Uranium Project,” the German nuclear program became known among its members by the less formal name of Uranverein or “Uranium Club.” And as German forces continued to storm across Europe, the Uranium Club steadily acquired the fruits of conquest: large stockpiles of Uranium from Belgium, a cyclotron particle accelerator from France, and a heavy-water production plant in Norway.

The various scientists who had fled Europe to escape Nazi persecution watched these developments with mounting apprehension. Among these were Albert Einstein and his Hungarian colleague Leo Szilard, who on August 2, 1939 – one month before the German invasion of Poland –  drafted a letter to U.S. President Franklin D. Roosevelt warning him of the grave danger posed by the German nuclear program:

“In the course of the last four months it has been made… possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.

 This new phenomenon would also lead to the construction of bombs, and it is conceivable – though much less certain – that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory.”

 This letter, along with similar warnings from other scientists, ultimately convinced Roosevelt to approve in June 1942 what became known as the Manhattan Project, with Army Corps of Engineers General Leslie Groves and physicist J. Robert Oppenheimer as its administrative and scientific directors, respectively – and for more on Einstein and Szilard’s other, more unexpected collaboration, please check out our previous video That Time Albert Einstein Decided to Try to Revolutionize Keeping Food Cold.

 At the time of the Manhattan Project’s inception, many scientists despaired that the Allies were at least 1-2 years behind the Germans in nuclear research, with physicist Leona Marshall Libby recalling:

“I think everyone was terrified that we were wrong, and the Germans were ahead of us.… Germany led the civilized world of physics in every aspect, at the time war set in, when Hitler lowered the boom. It was a very frightening time.”

A lack of reliable intelligence sources, however, prevented the Allies from gauging the progress of the German atomic bomb project. The Manhattan Project thus became a blind race against an unseen enemy, whose actual capabilities could only guessed at. Over the next three years some $32 billion dollars and 500,000 personnel – nearly 1% of the entire U.S. labour force – would be poured into beating the Germans to the finish line. As General Groves later wrote:

“Unless and until we had positive knowledge to the contrary, we had to assume that the most competent German scientists and engineers were working on an atomic program with the full support of their government and with the full capacity of German industry at their disposal. Any other assumption would have been unsound and dangerous.”

Indeed, the few scraps of intelligence the Allies were able to gather proved less than encouraging. In September 1941, Werner Heisenberg paid a visit to Danish physicist Niels Bohr at his home in Copenhagen. The purpose of the visit is the subject of considerable debate, with some historians claiming Heisenberg wanted to recruit Bohr into the German atomic bomb project and others that he tried to convince the Allies via Bohr to abandon their own nuclear program. What is known is that a) Bohr angrily expelled Heisenberg from his home and never spoke to him again; and b) during their meeting Heisenberg sketched for Bohr a simple diagram of a nuclear reactor. When Bohr was later evacuated from Denmark by the British he handed over this sketch to Allied intelligence, who took it as evidence that the Germans were far ahead in their nuclear research.

It was not until after the D-day landings in June 1944 that Allied intelligence finally began to pull back the curtain on the German Uranprojekt. The year before, U.S. Army Intelligence launched the ALSOS mission under the command of Lt. Colonel Boris T. Pash. Armed with a handful of jeeps and light weapons, ALSOS’s mission was to drive deep behind enemy lines and gather whatever information it could on the German nuclear project. But no matter how far they penetrated into occupied Europe and Germany itself, Colonel Pash and his men could find no evidence of the industrial-scale uranium enrichment facilities needed to produce an atomic bomb, and the few nuclear research facilities they did find were small-scale affairs run by university physics and chemistry departments. Finally, however, the ALSOS mission seemed to hit the jackpot when they discovered a full-scale nuclear reactor hidden in a beer cellar in the southern German town of Haigerloch. But when the reactor itself was examined and the scientists involved in its construction interrogated, it became clear that the Germans had never succeeded in achieving a sustained nuclear chain reaction. As the war in Europe finally came to an end and the available evidence was gathered, the ALSOS mission came to a startling conclusion: the Germans never came close to developing a working atomic bomb. None of the Uranium Club’s research on nuclear fission ever made it past the small-scale experimental stage, and the whole project was ultimately scrapped when the German High Command realized it would never contribute to the final outcome of the war. In an instant, the spectre of a German atomic bomb – the bogeyman that had kickstarted and sustained the gargantuan Manhattan Project – seemed to evaporate into thin air.

So…what happened? Why, despite having a two year head start over the Allies, did the German atomic bomb project ultimately fizzle out? There were many contributing factors, all of which illustrate the stark contrast between how scientific and technical development was carried out in Nazi Germany and the Allied nations.

The first nail in the coffin for the German atomic bomb project was the ruthless politicization of German science under the Nazi regime. By the time the Second World War broke out, the Nazis had thoroughly purged Germany’s universities and research institutes of Jews, communists, and other political undesirables – some 1,145 people or 14% of all higher educational staff. These included such superstars as Albert Einstein, Erwin Schrödinger, Hans Bethe, Eugene Wigner, Edward Teller, John von Neumann, and Otto Frisch – many of whom emigrated to the United States and became key figures in the Manhattan Project. Not even Werner Heisenberg was immune from Nazi suspicion. In 1938, Heisenberg came under attack from Reichsfuhrer Heinrich Himmler, head of the SS, who denounced him as a “white Jew” for his work on quantum theory and suggested he should be “made to disappear.” His reputation and career were only saved via the intervention of his mother, who happened to be old family friends with the Himmlers. As a result of this intervention Himmler realized that Germany could ill afford to lose such a great scientist and wrote Heisenberg a letter warning him to keep his physics and his politics separate. Such purges, along with the Nazi belief that atomic theory, quantum theory, and other recent scientific developments constituted degenerate “Jewish physics,” ultimately left Germany with few specialists capable of directing a successful nuclear research project. Furthermore, many of the scientists who remained in Germany were drafted into the armed forces, further reducing the scientific and technical capital available to the nation.

Another factor which ultimately sank the German atomic program was the convoluted and inefficient manner in which technical and scientific development was managed in Nazi Germany. Unlike in Allied nations like the United States where the Government decided which weapons projects were worth pursuing and assigned contracts to the companies best suited to completing them, in Germany multiple private firms, government departments, and branches of the armed forces competed with each other for limited resources and contracts. This was a deliberate divide-and-conquer tactic on the part of Hitler and his cronies, as it encouraged different government and military branches to bicker among themselves instead of conspiring against the regime. This system was also the product of the Nazis trying to square a particularly troublesome ideological circle. While the Nazis understood the advantages of free-market capitalism, they considered this an undesirable Jewish-American system and developed a strange hybrid arrangement of free enterprise and government control in an attempt to reconcile this contradiction. In practice, however, this lead to the wasteful duplication of effort and the squandering of limiting resources. For example, by the end of the war there were 86 different rocket projects in development, few of which ever reached operational status. Had the most promising of these projects been combined and assigned to a single contractor as in the Allied model, development would likely have proceeded far more efficiently. Similarly, at one point there were no less than three separate and independent nuclear research programs split up among nine research institutes in Berlin, Leipzig, and Kassel. According to German historian Klaus Hentschel:

“Compared with the British and American war research efforts united in the Manhattan Project, to this day the prime example of “big science,” the Uranverein was only a loosely knit, decentralized network of researchers with quite different research agendas. Rather than teamwork as on the American end, on the German side we find cut-throat competition, personal rivalries, and fighting over the limited resources.”

But even if the German nuclear project had been amalgamated into a single coordinated effort, it would still have been doomed by a lack of official government interest and support. While the Reichswehr saw the military potential nuclear fission early on, by mid-1940 that interest was rapidly fading as Germany’s rapid conquest of Western Europe convinced many in the High Command that the war would be won by 1942. This, along with the slow technical progress being made by the Uranium Club, convinced the Reichswehr that nuclear research would not contribute to ending the war in the short term. The project was thus handed over to the Reich Research Council in January 1942 and assigned a low priority. The goals of the project were also simplified from building an atomic bomb to building a nuclear reactor for research, energy generation, and possibly naval propulsion. The situation was not helped by the fact that Adolf Hitler, who had no background in science and technology, neither understood nor appreciated the potential of nuclear energy and gravitated instead towards less abstract “wonder weapons” like giant railway guns and ballistic missiles. The upshot of all this was that compared to the Manhattan Project, the German Uranium Club was woefully underfunded and understaffed, receiving the equivalent of only $2 million in government funds and employing a maximum of 100 researchers. Its American equivalent, by contrast, employed 5000x more personnel and received 16,000x more funding. And as the war dragged on the Uranium Club would only get smaller, its Uranium stockpiles diverted to make armour-piercing ammunition and its scientists assigned to more pressing military projects.

But the single greatest factor which ultimately sank the German atomic bomb project was, ironically, a lack of German scientific expertise. Despite Allied fears that the Germans were years ahead in nuclear research, by the time the Manhattan Project got underway in early 1942, British and American scientists had already pulled far ahead of their German counterparts. This was largely due to the aforementioned political purge of the German intelligentsia, which left the country with a shortage of experts on nuclear physics. This, in turn, lead to German scientists making a number of key errors that doomed the whole undertaking from the start. For example, to build a working nuclear reactor one needs not only Uranium as fuel, but also a material called a moderator. The moderator slows down neutrons produced by nuclear fissions to the optimum energy needed to produce additional fissions, thus sustaining the chain reaction. The world’s first nuclear reactor, Chicago Pile 1, used bricks of graphite, an ultra-pure form of carbon. However, this material was ruled out early in the German program when a calculation error led physicist Walther Bothe to conclude that it absorbed too many neutrons to be a practical moderator. This left only one choice: heavy water, a form of water  in which some of the hydrogen is replaced by the heavier isotope deuterium. At the time, there was only one source of heavy water in Europe: the Vermork Norsk Hydro plant in Telemark, Norway, where heavy water was generated as a byproduct of fertilizer production. The Germans invaded Norway in April 1940 and immediately began producing heavy water for their nuclear reactor project. The Allies, recognizing the strategic importance of the plant, launched a series of attacks including a February 1943 raid by Norwegian commandoes codenamed Operation Gunnerside, which succeeded in blowing up the heavy water production equipment. The Germans abandoned production and attempted to ship the remaining heavy water out of Norway, but were thwarted when the Norwegian resistance bombed and sank the ferry carrying the barrels across Lake Tinn.

As a result of this sabotage, German scientists working on reactors were left with a very limited quantity of poor-quality moderator, meaning that the original design of 664 3-inch Uranium cubes suspended on wires no longer had adequate critical mass to sustain a chain reaction. Then, in December 1942, shortly after Chicago Pile 1 first achieved criticality, air leaked into the German L-IV reactor in Leipzig and ignited the Uranium fuel, starting a fire that boiled the coolant and caused the reactor to explode. The entire facility was destroyed, forcing it to be abandoned.

There were other problems as well. Building a practical atomic bomb requires separating the rare fissile isotope Uranium-235 from the far more abundant but non-fissile isotope Uranium-238. This is a slow and highly energy-intensive process, so much so that the Manhattan Project, running three different enrichment processes simultaneously in some of the largest industrial facilities s ever constructed, only managed to enrich enough Uranium for a single bomb – and even then only after the war in Europe had ended. While the Germans experimented with various separation methods, they quickly realized that Germany simply lacked the resources and industrial might to enrich enough Uranium within a reasonable timeframe, with one scientist exclaiming upon learning of Hiroshima and Nagasaki:

“It must have taken factories large as the United States to make that much uranium-235!”  

 The only other option for building a bomb was to breed the fissile isotope Plutonium-239 from Uranium-238 in a reactor, but the Germans seem to have been unaware of this process and in any case never managed to get even a simple reactor working. Furthermore, even the most knowledgeable German scientists like Werner Heisenberg were unfamiliar with the fast neutron fission physics fundamental to the functioning of an atomic bomb, and thus would likely have been unable to build a functioning weapon even if they had managed to enrich sufficient Uranium. In conclusion, the German project failed because, unlike the Manhattan Project, it had nowhere near enough manpower, resources, centralization, government support, and technical backing. In short, it never had a chance.

Over the years, a myth has arisen that the German nuclear program failed due to internal sabotage. According to this theory, leading project scientists like Werner Heisenberg were opposed to developing nuclear weapons on moral grounds and actively worked to stall the project and deny Hitler the bomb. However, this notion appears to have been fabricated by these scientists in order to rehabilitate their post-war reputations, with historian and author Richard Rhodes concluding that:

 “There was at least one speculation that one of the German scientists deliberately falsified the measurements in graphite, hoping to stop a German bomb program. I don’t think there’s really evidence to support that. It seems to have been a mistake in the course of developing these various components of the technology.”

In the end, the German atomic bomb which had so frightened the Allies turned out to be nothing but a mirage, a half-hearted attempt mortally hobbled by the bureaucracy, ineptitude, and ideological corruption of the Nazi regime. But despite the fact that Adolf Hitler never came close to possessing nuclear weapons, the German project nonetheless had a profound impact on the post-war world order. Had the Allies known the true extent of German nuclear research, they might not have poured such vast resources into the Manhattan Project, the atomic bomb would not have been developed until years or even decades later, and the world as we know it would be a very different place.

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Expand for References

 Kant, Horst, Werner Heisenberg and the German Uranium Project, Max Planck Institute for the History of Science, 2002,


Mangravite, Andrew, Magical Thinking: What Happened to Physics in Nazi Germany? Science History Institute, December 16, 2015,


Easley, Matt, The Atomic Bomb That Never Was: Germany’s Atomic Bomb Project,


Williams, Joseph, The Secret World War II Mission to Kidnap Hitler’s A-Bomb Scientists, History, June 4, 2020,


Atomic Rivals and the ALSOS Mission, The Manhattan Project: an Interactive History, U.S. department of Energy,


German Atomic Bomb Project, Atomic Heritage Foundation, October 18, 2016,

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