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1890s-1939:
Atomic Discoveries

1939-1942:
Early
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1942:
Difficult
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1942-1944:
The Uranium
Path to
the Bomb

1942-1944:
The Plutonium
Path to
the Bomb

1942-1945:
Bringing It All Together

1945:
Dawn of the
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1945-present:
Postscript --
The Nuclear Age


Werner Heisenberg, the leader of the German atomic weapons program.ATOMIC RIVALS AND THE ALSOS MISSION
(Germany and Japan, 1938-1945)
Events > Bringing It All Together, 1942-1945

For most of the Second World War, scientists and administrators of the Manhattan Project firmly believed that they were in a race with Germany to develop the atomic bomb.  As it turns out, the German atomic program did not come close to developing a useable weapon.  Allied planners were only able to confirm this, however, through the ALSOS intelligence mission to Europe toward the end of the war. Atomic research was also conducted in Japan, but as was suspected by the Allies, it did not get very far.  

A captured German V-2 rocket being tested after the war, Cape Canaveral, Florida, July 24, 1950.Fission, the basic process that makes nuclear weapons possible, was first discovered in Berlin in December 1938.  Though the beginning of the war was still ten months away, when news of the German discovery arrived in the United States, it caused a considerable amount of alarm.  Not only did it now appear for the first time that an "atomic bomb" was possible, but it was Nazi Germany that seemed to be ahead in this new and potentially worst-of-all arms races.  Many of the scientists that took a leading role in alerting the United States government to this danger, such as Albert Einstein, Enrico Fermi, and Leo Szilard, were recent émigrés from Europe who felt the threat from Nazi Germany especially acutely.  Further, German science and industry appeared to be capable of the kind of massive development program that building an atomic bomb would require.  During the war, for example, Germany had become the first nation in the world to develop and use jet fighters (Me-262s), cruise missiles (V-1s), and ballistic missiles (V-2s).  Although we now know that the United States and Britain won the race for the bomb, it is important to remember that this outcome was by no means certain, let alone obvious, during the early years of the war.  

Paul HarteckThe German atomic weapons program began with a secret April 1939 conference in Berlin, which resulted in the Ministry of Education initiating a formal uranium research program and banning the export of uranium to other nations.  That same month, Paul Harteck (right), a German chemist, wrote the War Office to alert it to the danger of "an explosive many orders of magnitude more powerful than the conventional ones" that would give "that country which first makes use of it an unsurpassable advantage."  Hans Geiger (of "Geiger counter" fame) confirmed that this was a very real possibility, and the War Office threw its support behind uranium research.  The "German Manhattan Project" had begun, five  months before President Franklin D. Roosevelt would read Einstein's letter warning of the potential for nuclear weapons.  

Kurt DiebnerThe most destructive war in human history began with the German invasion of Poland on September 1, 1939. That same month Kurt Diebner (left), the head of the War Office's fission research, summoned Geiger, Otto Hahn (below left), and other physicists to Berlin to discuss the feasibility of nuclear weapons.  By the end of a second meeting that month (to which Werner Heisenberg had been invited as well), the German scientists had agreed to begin research into pile design, isotope separation, fast-neutron fission, and other critical aspects of an atomic weapons program.  German uranium research continued and, in 1940, it began to benefit from the successes of the Nazi armies that were overrunning Western Europe. In Belgium, Germany captured an ample supply of uranium; in France, Germany captured Frédéric Joliot and his cyclotron; in Norway, Germany captured a Norsk Hydro Plant that was the world's largest producer of heavy water; and in Denmark, Germany captured Niels Bohr. (The American embassy had offered Bohr safe passage to the United States during the invasion, but Bohr chose to stay behind and help organize the peaceful resistance to the Nazi occupation.)  By October 1940, Heisenberg was conducting at the Kaiser-Wilhelm Institute a series of pile experiments that were comparable to those being carried out that same year by Fermi at Columbia University.  The race still appeared to be neck-and-neck.  

Otto HahnAlthough there was no way for the Americans to know it at the time, scientists in the United States began in around 1941 to pull far ahead of their counterparts in Germany.  In January of that year, a physicist by the name of Walter Bothe made a critical miscalculation that caused Germany to mistakenly rule out graphite as a possible moderator. (Szilard had recently succeeded in convincing scientists in the still-neutral United States to keep secret the results of their atomic research, and, as a result, the Germans could not learn of their mistake from the open scientific literature.)  This left expensive heavy water as the only viable moderator for a pile, and the plutonium path to the bomb was only possible if a chain-reacting pile could first be made to work.  As for the uranium path to the bomb, German researchers concentrated most of their early isotope separation effort on theLiquid thermal diffusion method for the enrichment of uranium. inefficient thermal diffusion method (left). After this was eventually abandoned, they concluded that the other methods of producing weapons-grade uranium would only be possible at a very great expense and with no assurance of success.  (They were correct in this.  It took years of extremely expensive work at Oak Ridge to produce enough uranium-235 for one atomic bomb.)  Thus, by mid-1941, German researchers had become quite pessimistic about the feasibility of any sort of nuclear weapon.  

German atomic research began to languish.  The notoriously inefficient Nazi bureaucracy, as well as possible doubts by German scientists about the Nazi regime itself, contributed to the ineffectiveness of German atomic research.  In 1941, the German Post Office was also funding uranium research separately from Heisenberg's work with the War Office.  A physicist by the name of Fritz Houterman was closely associated with this effort, however, and he withheld as much information as he could from his German superiors, possibly attempting to discourage further uranium research in favor of the more complicated plutonium route.  (Houterman, a half-Jewish Austrian communist, held no love for the Nazis.)  After the war, many other German physicists, including most notably Heisenberg himself, also claimed to have been secretly not trying very hard in their war research.  Whether this was an attempt after the fact to excuse their failure and/or justify their work on behalf of the Nazi regime is still a subject of intense debate among historians today.

Werner Heisenberg and Niels Bohr, 1934An incident in September 1941 helps to illustrate the confused and ambiguous nature of possible resistance by German scientists to the German atomic bomb project.  Heisenberg, who by this time was the leader of the German effort, asked for a meeting with his old friend and mentor Bohr.  According to Heisenberg, he was there to ask Bohr's opinion of the morality of work on the atomic bomb.  For his part, Bohr wanted no part of German atomic research and was careful to say nothing of importance.  Heisenberg did tell Bohr of Germany's atomic research and even passed to Bohr a diagram of the German pile in Berlin, but whether he did so in order to warn Bohr, and hence the Allies, or only to get Bohr's advice (or even mislead him), it is impossible to know.  In 1943, the Danish underground helped Bohr to escape to Britain (via neutral Sweden).  He got away only days before he was to be arrested by the Gestapo, and he brought with him the drawing of Heisenberg's pile.  

Comparatively little progress was made toward a German atomic bomb from about 1942 onwards.  Many German scientists, including Heisenberg, continued to make pleas for greater government funding, but as the war turned against Germany, it increasingly focused its science and industry on more immediate war needs.  German pile work continued to focus until the end on heavy water piles, and this work was hampered by a series of attacks that were made on the Norsk Hydro heavy water plant by American aircraft, British commandos, and the Norwegian resistance.  In the final year of the war, aerial bombing and eventually the advance of Allied ground troops also disrupted their research.  When Germany surrendered in May 1945, its atomic researchers were still struggling to reach critical mass with a pile, a goal Fermi had first achieved at the Met Lab in December 1942.  

American troops approaching the beach, D-Day, June 6, 1944.For most of the war, however, the success or failure of the German atomic program remained unknown to the Allies who knew little about what progress, if any, had been made. They knew that Germany had gathered sufficient quantities of uranium to do research and that it was very interested in the Norwegian heavy water, but beyond that there were only rumors.  When Bohr told scientists at Los Alamos of his strange conversation with Heisenberg, no one was certain quite what to make of the unusual German pile design.  At that point, they knew for certain that Germany was pursuing nuclear weapons but little else was clear.  After Allied troops landed in France on June 6, 1944 ("D-Day," right), it finally became possible to physically search Europe for signs of German atomic research.  This was accomplished by the "ALSOS Mission."  

Farm HallThe ALSOS team was led by Lt. Colonel Boris T. Pash, an Army intelligence officer who had earlier taken part in the security investigation of Robert Oppenheimer.  Because the members of the ALSOS team would at times be going into "no man's land" -- or even behind enemy lines -- in search of information, they were not told any details of the Manhattan Project.  This way, if they were captured, they could reveal nothing of use to the Germans.  The mission began in Italy and followed closely behind the Allied armies as they pushed deeper into Europe and, ultimately, into Germany itself.  Although proving a negative is always difficult, after months of investigation the ALSOS team found no indications of massive German nuclear production facilities of the sort that had been built at Hanford or Oak Ridge. In late November 1944, ALSOS representatives uncovered strong evidence at the University of Strasbourg that the German program had not gotten beyond the research and development stage, but it was not until April 1945, only weeks before the final German surrender, that the bulk of the German uranium was captured and any final fears of a Nazi bomb were alleviated.  After the war, ten of the top German atomic researchers were interned in a British intelligence "safe house" in Farm Hall, Great Britain (above left), for six months.  All of their conversations were secretly recorded.  The significance of what they said to each other is still a matter of debate, but the transcripts of their discussions do make it clear just how far away from a useable weapon the German atomic program remained at war's end.  

With the surrender of Germany, only Japan remained as a possible atomic threat.  Japanese physicists had noted the discovery of fission before the war, and they did inform the Japanese Army of the danger.  Some research was conducted at a Tokyo laboratory into various methods of uranium enrichment, but comparatively little progress was made.  In early 1943, a group of Japanese experts concluded that, while it was true that the United States was probably trying to build an atomic bomb, it might take Japan ten years or more to build one.  Accordingly, little further research into nuclear energy was conducted in Japan beyond the construction of one cyclotron in Kyoto.

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Sources and notes for this page.

The text for this page is original to the Department of Energy's Office of History and Heritage Resources.  "Atomic" and "nuclear" are basically synonymous; much as the term "pile" gradually gave way to "reactor," "atomic" was gradually replaced by "nuclear" during the later years of the Manhattan Project and afterwards.  For the German atomic program, see David Irving, The German Atomic Bomb (New York: Simon and Schuster, 1968).  On the ALSOS mission, see Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 280-291.  For the Japanese program, see Pacific War Research Society, The Day Man Lost (Kodansha International, 1972), and Deborah Shapley, "Nuclear Weapons History: Japan's Wartime Bomb Projects Revealed," Science 199 (1978), 152.  It should be noted also that two authors have in recent years argued Japan and Germany were much closer than has been generally realized to developing nuclear weapons.  In Japan's Secret War: Japan's Race Against Time to Build Its Own Atomic Bomb (New York: Marlowe & Company, 1995), Robert K. Wilcox argues that Japan came extremely close to completing a bomb.  In The Nuclear Axis: Germany, Japan and the Atom Bomb Race, 1939-1945 (Phoenix Mill, UK: Sutton Publishing Limited, 2000), Philip Henshall implies that both Germany and Japan made much more progress than is generally known and that this may have been covered up by the Allies for some reason that relates somehow to the Cold War.  Neither author provides footnotes, however, and it is therefore often impossible to determine what their source is for any particular statement.  Further, their most important (and controversial) arguments often rely more on supposition and the raising of "unanswered questions" than on detailed, verifiable evidence.  Their arguments have not been generally accepted within the historical profession.  Still, there is interesting information in both regarding their subjects, and -- used with caution -- they can be useful sources of information.  The photograph of the V-2 rocket being tested in Florida after the war is courtesy the National Oceanic and Atmospheric Administration's photo library.  The photograph of Werner Heisenberg with Niels Bohr is courtesy the Fermi National Accelerator Laboratory.  The diagram illustrating the liquid thermal diffusion method is reproduced from the Department of Energy report Linking Legacies: Connecting the Cold War Nuclear Weapons Production Processes to their Environmental Consequences (Washington: Center for Environmental Management Information, Department of Energy, January 1997), 138.  The photograph of "D-Day" is courtesy the National Archives (NARA).  All other photographs are courtesy NARA and are reprinted in Jeremy Bernstein, ed., Hitler's Uranium Club: The Secret Recordings at Farm Hall (Woodbury, NY: American Institute of Physics, 1996).

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