German nuclear weapon project

The German nuclear weapon project (Uranprojekt; informally known as the Uranverein; Uranium Society or Uranium Club), was a clandestine scientific effort led by Germany to develop and produce nuclear weapons during World War II. This program started in April 1939, just months after the discovery of nuclear fission in January 1939, but ended only months later due to the German invasion of Poland, after many notable physicists were drafted into the Wehrmacht.

A second effort began under the administrative purview of the Wehrmacht's  Heereswaffenamt on 1 September 1939, the day of the Invasion of Poland. The program eventually expanded into three main efforts: the Uranmaschine (nuclear reactor), uranium and heavy water production, and uranium isotope separation. Eventually it was assessed that nuclear fission would not contribute significantly to ending the war, and in January 1942, the Heereswaffenamt turned the program over to the Reich Research Council while continuing to fund the program. The program was split up among nine major institutes where the directors dominated the research and set their own objectives. Subsequently, the number of scientists working on applied nuclear fission began to diminish, with many applying their talents to more pressing war-time demands.

The most influential people in the Uranverein were Kurt Diebner, Abraham Esau, Walther Gerlach, and Erich Schumann; Schumann was one of the most powerful and influential physicists in Germany. Diebner, throughout the life of the nuclear weapon project, had more control over nuclear fission research than did Walther Bothe, Klaus Clusius, Otto Hahn, Paul Harteck, or Werner Heisenberg. Abraham Esau was appointed as Hermann Göring's plenipotentiary for nuclear physics research in December 1942; Walther Gerlach succeeded him in December 1943.

Politicization of the German academia under the National Socialist regime had driven many physicists, engineers, and mathematicians out of Germany as early as 1933. Those of Jewish heritage who did not leave were quickly purged from German institutions, further thinning the ranks of academia. The politicization of the universities, along with the demands for manpower by the German armed forces (many scientists and technical personnel were conscripted, despite possessing useful skills), would eventually all but eliminate a generation of physicists.

At the end of the war, the Allied powers competed to obtain surviving components of the nuclear industry (personnel, facilities, and materiel), as they did with the V-2 program.

Discovery of nuclear fission
In December 1938, German chemists Otto Hahn and Fritz Strassmann sent a manuscript to the science journal Naturwissenschaften ("Natural Science") reporting they had detected the element barium after bombarding uranium with neutrons; simultaneously, they communicated these results to Lise Meitner, who had fled Germany in July to the Netherlands and then to Sweden. Meitner, and her nephew Otto Robert Frisch, correctly interpreted these results as being nuclear fission. Frisch confirmed this experimentally on 13 January 1939.

First Uranverein
Paul Harteck was director of the physical chemistry department at the University of Hamburg and an advisor to the Heereswaffenamt (HWA, Army Ordnance Office). On 24 April 1939, along with his teaching assistant Wilhelm Groth, Harteck made contact with the Reichskriegsministerium (RKM, Reich Ministry of War) to alert them to the potential of military applications of nuclear chain reactions. Two days earlier, on 22 April 1939, after hearing a colloquium paper by Wilhelm Hanle on the use of uranium fission in a Uranmaschine (uranium machine, i.e., nuclear reactor), Georg Joos, along with Hanle, notified Wilhelm Dames, at the Reichserziehungsministerium (REM, Reich Ministry of Education), of potential military applications of nuclear energy. The communication was given to Abraham Esau, head of the physics section of the Reichsforschungsrat (RFR, Reich Research Council) at the REM. On 29 April, a group, organized by Esau, met at the REM to discuss the potential of a sustained nuclear chain reaction. The group included the physicists Walther Bothe, Robert Döpel, Hans Geiger, Wolfgang Gentner (probably sent by Walther Bothe), Wilhelm Hanle, Gerhard Hoffmann, and Georg Joos; Peter Debye was invited, but he did not attend. After this, informal work began at the Georg-August University of Göttingen by Joos, Hanle, and their colleague Reinhold Mannkopff; the group of physicists was known informally as the first Uranverein (Uranium Club) and formally as Arbeitsgemeinschaft für Kernphysik. The group's work was discontinued in August 1939, when the three were called to military training.

Another notification
The industrial firm Auergesellschaft had a substantial amount of "waste" uranium from which it had extracted radium. After reading a June 1939 paper by Siegfried Flügge, on the technical use of nuclear energy from uranium, Nikolaus Riehl, the head of the scientific headquarters at Auergesellschaft, recognized a business opportunity for the company, and in July he went to the HWA (Heereswaffenamt, Army Ordnance Office) to discuss the production of uranium. The HWA was interested and Riehl committed corporate resources to the task. The HWA eventually provided an order for the production of uranium oxide, which took place in the Auergesellschaft plant in Oranienburg, north of Berlin.

Second Uranverein
The second Uranverein began after the Heereswaffenamt (HWA, Army Ordnance Office) squeezed out the Reichsforschungsrat (RFR, Reich Research Council) of the Reichserziehungsministerium (REM, Reich Ministry of Education) and started the formal German nuclear weapons project under military auspices. The second Uranverein was formed on 1 September 1939, the day World War II began, and it had its first meeting on 16 September 1939. The meeting was organized by Kurt Diebner, advisor to the HWA, and held in Berlin. The invitees included Walther Bothe, Siegfried Flügge, Hans Geiger, Otto Hahn, Paul Harteck, Gerhard Hoffmann, Josef Mattauch, and Georg Stetter. A second meeting was held soon thereafter and included Klaus Clusius, Robert Döpel, Werner Heisenberg, and Carl Friedrich von Weizsäcker. Also at this time, the Kaiser-Wilhelm Institut für Physik (KWIP, Kaiser Wilhelm Institute for Physics, after World War II the Max Planck Institute for Physics), in Berlin-Dahlem, was placed under HWA authority, with Diebner as the administrative director, and the military control of the nuclear research commenced.

When it was apparent that the nuclear weapon project would not make a decisive contribution to ending the war in the near term, control of the KWIP was returned in January 1942 to its umbrella organization, the Kaiser-Wilhelm Gesellschaft (KWG, Kaiser Wilhelm Society, after World War II the Max-Planck Gesellschaft), and HWA control of the project was relinquished to the RFR in July 1942. The nuclear weapon project thereafter maintained its kriegswichtig (important for the war) designation and funding continued from the military. However, the German nuclear power project was then broken down into the following main areas: uranium and heavy water production, uranium isotope separation, and the Uranmaschine (uranium machine, i.e., nuclear reactor). Also, the project was then essentially split up between a number of institutes, where the directors dominated the research and set their own research agendas. The dominant personnel, facilities, and areas of research were:
 * Walther Bothe — Director of the Institut für Physik (Institute for Physics) at the Kaiser-Wilhelm Institut für medizinische Forschung (KWImF, Kaiser Wilhelm Institute for Medical Research, after 1948 the Max-Planck-Institut für medizinische Forschung), in Heidelberg.
 * Measurement of nuclear constants. (6 physicists)
 * Klaus Clusius — Director of the Institute for Physical Chemistry at the Ludwig Maximilian University of Munich
 * Isotope separation and heavy water production. (ca. 4 physical chemists and physicists)
 * Kurt Diebner — Director of the HWA Versuchsstelle (testing station) in Gottow; Diebner, was also director the RFR experimental station in Stadtilm, Thuringia. He was also an advisor to the HWA on nuclear physics.
 * Measurement of nuclear constants. (ca. 6 physicists)
 * Otto Hahn — Director of the Kaiser-Wilhelm-Institut für Chemie (KWIC, Kaiser Wilhelm Institute for Chemistry, after World War II the Max Planck Institut für Chemie — Otto Hahn Institut), in Berlin-Dahlem.
 * Transuranic elements, fission products, isotope separation, and measurement of nuclear constants. (ca. 6 chemists and physicists)
 * Paul Harteck — Director of the Physical Chemistry Department of the University of Hamburg.
 * Heavy water production and isotope production. (5 physical chemists, physicists, and chemists)
 * Werner Heisenberg — Director of the Department of Theoretical Physics at the University of Leipzig until summer 1942. Thereafter acting director of the Kaiser-Wilhelm-Institut für Physik (Kaiser Wilhelm Institute for Physics), in Berlin-Dahlem.
 * Uranmaschine, isotope separation, and measurement of nuclear constants. (ca. 7 physicists and physical chemists).
 * Hans Kopfermann — Director of the Second Experimental Physics Institute at the Georg-August University of Göttingen.
 * Isotope separation. (2 physicists)
 * Nikolaus Riehl — Scientific Director of the Auergesellschaft.
 * Uranium production. (ca. 3 physicists and physical chemists)
 * Georg Stetter — Director of the II. Physikalisches Institut (Second Physics Institute) at the University of Vienna.
 * Transuranic elements and measurement of nuclear constants. (ca. 6 physicists and physical chemists)

The point in 1942, when the army relinquished its control of the German nuclear weapon project, was the zenith of the project relative to the number of personnel devoted to the effort. There were only about seventy scientists working on the project, with about forty devoting more than half their time to nuclear fission research. After this, the number of scientists working on applied nuclear fission diminished dramatically. Many of the scientists not working with the main institutes stopped working on nuclear fission and devoted their efforts to more pressing war related work.

On 4 June 1942, a conference initiated by the "Reich Minister for Armament and Ammunition" Albert Speer regarding the nuclear weapon project, had decided its continuation merely for the aim of energy production. On 9 June 1942, Adolf Hitler issued a decree for the reorganization of the RFR as a separate legal entity under the Reichsministerium für Bewaffnung und Munition (RMBM, Reich Ministry for Armament and Ammunition, after late 1943 the Reich Ministry for Armament and War Production); the decree appointed Reich Marshal Hermann Göring as the president. The reorganization was done under the initiative of Minister Albert Speer of the RMBM; it was necessary as the RFR under Minister Bernhard Rust was ineffective and not achieving its purpose. It was the hope that Göring would manage the RFR with the same discipline and efficiency as he had in the aviation sector. A meeting was held on 6 July 1942 to discuss the function of the RFR and set its agenda. The meeting was a turning point in National Socialism's attitude towards science, as well as recognition that its policies which drove Jewish scientists out of Germany were a mistake, as the Reich needed their expertise. Abraham Esau was appointed on 8 December 1942 as Hermann Göring's Bevollmächtigter (plenipotentiary) for nuclear physics research under the RFR; in December 1943, Esau was replaced by Walther Gerlach. In the final analysis, placing the RFR under Göring's administrative control had little effect on the German nuclear weapon project.

Over time, the HWA and then the RFR controlled the German nuclear weapon project. The most influential people were Kurt Diebner, Abraham Esau, Walther Gerlach, and Erich Schumann. Schumann was one of the most powerful and influential physicists in Germany. Schumann was director of the Physics Department II at the Frederick William University (later, University of Berlin), which was commissioned and funded by the Oberkommando des Heeres (OKH, Army High Command) to conduct physics research projects. He was also head of the research department of the HWA, assistant secretary of the Science Department of the OKW, and Bevollmächtigter (plenipotentiary) for high explosives. Diebner, throughout the life of the nuclear weapon project, had more control over nuclear fission research than did Walther Bothe, Klaus Clusius, Otto Hahn, Paul Harteck, or Werner Heisenberg.

Isotope separation
Heinz Ewald, a member of the Uranverein, had proposed an electromagnetic isotope separator, which was thought applicable to U235 production and enrichment. This was picked up by Manfred von Ardenne, who ran a private research establishment.

In 1928, von Ardenne had come into his inheritance with full control as to how it could be spent, and he established his private research laboratory the Forschungslaboratoriums für Elektronenphysik, in Berlin-Lichterfelde, to conduct his own research on radio and television technology and electron microscopy. He financed the laboratory with income he received from his inventions and from contracts with other concerns. For example, his research on nuclear physics and high-frequency technology was financed by the Reichspostministerium (RPM, Reich Postal Ministry), headed by Wilhelm Ohnesorge. Von Ardenne attracted top-notch personnel to work in his facility, such as the nuclear physicist Fritz Houtermans, in 1940.

Von Ardenne had also conducted research on isotope separation. Taking Ewald's suggestion he began building a prototype for the RPM. The work was hampered by war shortages and ultimately ended by the war.

Moderator production
The production of heavy water was already under way in Norway when the Nazis invaded on 9 April 1940. The Norwegian production of heavy water was quickly secured and improved by Nazis. The takeover and eventual sabotage is described in Norwegian heavy water sabotage.

Internal reports
Reports from the research conducted were published in Kernphysikalische Forschungsberichte (Research Reports in Nuclear Physics), an internal publication of the Uranverein. The reports were classified Top Secret, they had very limited distribution, and the authors were not allowed to keep copies. The reports were confiscated under the Allied Operation Alsos and sent to the United States Atomic Energy Commission for evaluation. In 1971, the reports were declassified and returned to Germany. The reports are available at the Karlsruhe Nuclear Research Center and the American Institute of Physics.

Individual reports are cited on the pages for some of the research participants in the Uranverein; see for example Friedrich Bopp, Kurt Diebner, Klara Döpel, Robert Döpel, Siegfried Flügge, Paul Harteck, Walter Herrmann, Karl-Heinz Höcker, Fritz Houtermans, Horst Korsching, Georg Joos, Heinz Pose, Carl Ramsauer, Fritz Strassmann, Karl Wirtz, and Karl Zimmer.

Politicization
Two factors which had deleterious effects on the nuclear weapon project were the politicization of the education system under National Socialism and the rise of the Deutsche Physik movement, which was anti-Semitic and had a bias against theoretical physics, especially quantum mechanics.

Emigrations
Adolf Hitler took power on 30 January 1933. On 7 April, the Law for the Restoration of the Professional Civil Service was enacted; this law, and its subsequent related ordinances, politicized the education system in Germany. This had immediate deleterious effects on the physics capabilities of Germany. Furthermore, combined with the Deutsche Physik movement, the deleterious effects were intensified and prolonged. The consequences to physics in Germany and its subfield of nuclear physics were multifaceted.

An immediate consequence upon passage of the law was that it produced both quantitative and qualitative losses to the physics community. Numerically, it has been estimated that a total of 1,145 university teachers, in all fields, were driven from their posts, which represented about 14% of the higher learning institutional staff members in 1932–1933. Out of 26 German nuclear physicists cited in the literature before 1933, 50% emigrated. Qualitatively, 10 physicists and four chemists who had won or would win the Nobel Prize emigrated from Germany shortly after Hitler came to power, most of them in 1933. These 14 scientists were: Hans Bethe, Felix Bloch, Max Born, Albert Einstein, James Franck, Peter Debye, Dennis Gabor, Fritz Haber, Gerhard Herzberg, Victor Hess, George de Hevesy, Erwin Schrödinger, Otto Stern, and Eugene Wigner. Britain and the USA were often the recipients of the talent which left Germany. The University of Göttingen had 45 dismissals from the staff of 1932–1933, for a loss of 19%. Eight students, assistants, and colleagues of the Göttingen theoretical physicist Max Born left Europe after Hitler came to power and eventually found work on the Manhattan Project, thus helping the United States, Britain and Canada to develop the atomic bomb; they were Enrico Fermi, James Franck, Maria Goeppert-Mayer, Robert Oppenheimer (who was American, but had studied under Born), Edward Teller, Victor Weisskopf, Eugene Wigner, and John von Neumann. Otto Robert Frisch, who with Rudolf Peierls first calculated the critical mass of U-235 needed for an explosive, was also a Jewish refugee.

Max Planck, the father of quantum theory, had been right in assessing the consequences of National Socialist policies. In 1933, Planck, as president of the Kaiser Wilhelm Gesellschaft (Kaiser Wilhelm Society), met with Adolf Hitler. During the meeting, Planck told Hitler that forcing Jewish scientists to emigrate would mutilate Germany and the benefits of their work would go to foreign countries. Hitler responded with a rant against Jews and Planck could only remain silent and then take his leave. The National Socialist regime would only come around to the same conclusion as Planck in the 6 July 1942 meeting regarding the future agenda of the Reichsforschungsrat (RFR, Reich Research Council), but by then it was too late.

Heisenberg affair
The politicization of the education system essentially replaced academic tradition and excellence with ideological adherence and trappings, such as membership in National Socialist organizations, such as the Nationalsozialistische Deutsche Arbeiterpartei (NSDAP, National Socialist German Workers Party), the Nationalsozialistischer Deutscher Dozentenbund (NSDDB, National Socialist German University Lecturers League), and the Nationalsozialistischer Deutscher Studentenbund (NSDStB, National Socialist German Student League). The politicization can be illustrated with the conflict which evolved when a replacement for Arnold Sommerfeld was sought in view of his emeritus status. The conflict involved one of the prominent Uranverein participants, Werner Heisenberg.

On 1 April 1935 Arnold Sommerfeld, Heisenberg's teacher and doctoral advisor at the University of Munich, achieved emeritus status. However, Sommerfeld stayed on as his own temporary replacement during the selection process for his successor, which took until 1 December 1939. The process was lengthy due to academic and political differences between the Munich Faculty's selection and that of both the Reichserziehungsministerium (REM, Reich Education Ministry) and the supporters of Deutsche Physik. In 1935, the Munich Faculty drew up a candidate list to replace Sommerfeld as ordinarius professor of theoretical physics and head of the Institute for Theoretical Physics at the University of Munich. There were three names on the list: Werner Heisenberg, who received the Nobel Prize in Physics in 1932, Peter Debye, who would receive the Nobel Prize in Chemistry in 1936, and Richard Becker — all former students of Sommerfeld. The Munich Faculty was firmly behind these candidates, with Heisenberg as their first choice. However, supporters of Deutsche Physik and elements in the REM had their own list of candidates and the battle commenced, dragging on for over four years.

During this time, Heisenberg came under vicious attack by the supporters of Deutsche Physik. One such attack was published in Das Schwarze Korps, the newspaper of the Schutzstaffel, or SS, headed by Heinrich Himmler. In the editorial, Heisenberg was called a "White Jew" who should be made to "disappear." These verbal attacks were taken seriously, as Jews were subject to physical violence and incarceration at the time. Heisenberg fought back with an editorial and a letter to Himmler, in an attempt to get a resolution to this matter and regain his honour. At one point, Heisenberg's mother visited Himmler's mother to help bring a resolution to the affair. The two women knew each other as a result of Heisenberg's maternal grandfather and Himmler's father being rectors and members of a Bavarian hiking club. Eventually, Himmler settled the Heisenberg affair by sending two letters, one to SS-Gruppenführer Reinhard Heydrich and one to Heisenberg, both on 21 July 1938. In the letter to Heydrich, Himmler said Germany could not afford to lose or silence Heisenberg as he would be useful for teaching a generation of scientists. To Heisenberg, Himmler said the letter came on recommendation of his family and he cautioned Heisenberg to make a distinction between professional physics research results and the personal and political attitudes of the involved scientists. The letter to Heisenberg was signed under the closing "Mit freundlichem Gruss und, Heil Hitler!" ("With friendly greetings and, Heil Hitler!")

Overall, the settlement of the Heisenberg affair was a victory for academic standards and professionalism. However, the replacement of Sommerfeld by Wilhelm Müller on 1 December 1939 was a victory of politics over academic standards. Müller was not a theoretical physicist, had not published in a physics journal, and was not a member of the Deutsche Physikalische Gesellschaft (DPG, German Physical Society); his appointment as a replacement for Sommerfeld was considered a travesty and detrimental to educating a new generation of theoretical physicists.

Missing generation of physicists
Politicization of the academic community, combined with the impact of the Deutsche Physik movement and other policies, such as drafting physicists to fight in the war (e.g., Paul O. Müller, a member of the Uranverein who died on the Russian front), had the net effect of bringing about a missing generation of physicists. At the close of the war, physicists born between 1915 and 1925 were almost nonexistent.

Autonomy and accommodation
Members of the Uranverein, Wolfgang Finkelnburg, Werner Heisenberg, Carl Ramsauer, and Carl Friedrich von Weizsäcker were effective in countering the politicization of academia and effectively putting an end to the influence of the Deutsche Physik movement. However, in order to do this they were, as were many scientists, caught between autonomy and accommodation. Essentially, they would have to legitimize the National Socialist system by compromise and collaboration.

During the period in which Deutsche Physik was gaining prominence, a foremost concern of the great majority of scientists was to maintain autonomy against political encroachment. Some of the more established scientists, such as Max von Laue, could demonstrate more autonomy than the younger and less established scientists. This was, in part, due to political organizations, such as the Nationalsozialistischer Deutscher Dozentenbund (National Socialist German University Lecturers League), whose district leaders had a decisive role in the acceptance of an Habilitationsschrift, which was a prerequisite to attaining the rank of Privatdozent necessary to becoming a university lecturer. While some with ability joined such organizations out of tactical career considerations, others with ability and adherence to historical academic standards joined these organizations to moderate their activities. This was the case of Finkelnburg. In mid-1940 Finkelnburg became an acting director of the NSDDB at Technische Hochschule, Darmstadt. As such, he organized the Münchner Religionsgespräche, which took place on 15 November 1940 and was known as the Munich Synod . The Münchner Religionsgespräche was an offensive against deutsche Physik. While the technical outcome may have been thin, it was a political victory against deutsche Physik. Also, in part, it was Finkelnburg's role in organising this event that influenced Carl Ramsauer, as president of the Deutsche Physikalische Gesellschaft, to select Finkelnburg in 1941 as his deputy. Finkelnburg served in this capacity until the end of World War II.

Early in 1942, as president of the DPG, Ramsauer, on Felix Klein's initiative and with the support of Ludwig Prandtl, submitted a petition to Reich Minister Bernhard Rust, at the Reichserziehungsministerium (Reich Education Ministry). The petition, a letter and six attachments, addressed the atrocious state of physics instruction in Germany, which Ramsauer concluded was the result of politicization of education.

Exploitation and denial
Near the end of World War II, the principal Allied war powers made plans for exploitation of German science. In light of the implications of nuclear weapons, German nuclear fission and related technologies were singled out for special attention. In addition to exploitations, denial was an element of their efforts, i.e., the Americans and Soviets conducted their respective operations to try to deny German technology, personnel, and material to the other party. Application of denial often meant getting there first, which to some extent put the Soviets at a disadvantage in some geographic locations, even if the area was to be in the Soviet zone of occupation. When it came to applications of exploitation and denial, all parties were sometimes heavy-handed.

A general US denial and exploitation effort was Operation Paperclip. Operations directed specifically towards German nuclear fission were Operation Alsos and Operation Epsilon, the latter being done in collaboration with the British. In lieu of the codename for the Soviet operation, if it had one, it has been referred to by Oleynikov as the Russian "Alsos".

American and British
Berlin had been a location of many German scientific research facilities. To limit casualties and loss of equipment, many of these facilities were dispersed to other locations in the latter years of the war.

Unfortunately for the Soviets, the Kaiser-Wilhelm-Institut für Physik (KWIP, Kaiser Wilhelm Institute for Physics) had mostly been moved in 1943 and 1944 to Hechingen and its neighboring town of Haigerloch, on the edge of the Black Forest, which eventually became the French occupation zone. This move allowed the Americans to take into custody a large number of German scientists associated with nuclear research. The only section of the institute which remained in Berlin was the low-temperature physics section, headed by Ludwig Bewilogua, who was in charge of the exponential uranium pile.

Nine of the prominent German scientists who published reports in Kernphysikalische Forschungsberichte as members of the Uranverein were picked up by Operation Alsos and incarcerated in England under Operation Epsilon: Erich Bagge, Kurt Diebner, Walther Gerlach, Otto Hahn, Paul Harteck, Werner Heisenberg, Horst Korsching, Carl Friedrich von Weizsäcker, and Karl Wirtz. Also, incarcerated was Max von Laue, although he had nothing to do with the nuclear weapon project. Goudsmit, the chief scientific advisor to Operation Alsos, thought von Laue might be beneficial to the postwar rebuilding of Germany and would benefit from the high level contacts he would have in England.

With the interest of the Heereswaffenamt (HWA, Army Ordnance Office), Nikolaus Riehl, and his colleague Günter Wirths, set up an industrial-scale production of high-purity uranium oxide at the Auergesellschaft plant in Oranienburg. Adding to the capabilities in the final stages of metallic uranium production were the strengths of the Degussa corporation's capabilities in metals production.
 * Oranienburg Plant

The Oranienburg plant provided the uranium sheets and cubes for the Uranmaschine experiments conducted at the KWIP and the Versuchsstelle (testing station) of the Heereswaffenamt (Army Ordnance Office) in Gottow. The G-1 experiment performed at the HWA testing station, under the direction of Kurt Diebner, had lattices of 6,800 uranium oxide cubes (about 25 tons), in the nuclear moderator paraffin.

Work of the American Operation Alsos teams, in November 1944, uncovered leads which took them to a company in Paris that handled rare earths and had been taken over by the Auergesellschaft. This, combined with information gathered in the same month through an Alsos team in Strasbourg, confirmed that the Oranienburg plant was involved in the production of uranium and thorium metals. Since the plant was to be in the future Soviet zone of occupation and the Red Army's troops would get there before the Allies, General Leslie Groves, commander of the Manhattan Project, recommended to General George Marshall that the plant be destroyed by aerial bombardment, in order to deny its uranium production equipment to the Soviets. On 15 March 1945, 612 B-17 Flying Fortress bombers of the Eighth Air Force dropped 1,506 tons of high-explosive and 178 tons of incendiary bombs on the plant. Riehl visited the site with the Soviets and said that the facility was mostly destroyed. Riehl also recalled long after the war that the Soviets knew precisely why the Americans had bombed the facility — the attack had been directed at them rather than the Germans.

French
From 1941 to 1947, Fritz Bopp was a staff scientist at the KWIP, and worked with the Uranverein. In 1944, when most of the KWIP was evacuated to Hechingen in Southern Germany due to air raids on Berlin, he went there too, and he was the Institute's Deputy Director there. When the American Alsos Mission evacuated Hechingen and Haigerloch, near the end of World War II, French armed forces occupied Hechingen. Bopp did not get along with them and described the initial French policy objectives towards the KWIP as exploitation, forced evacuation to France, and seizure of documents and equipment. The French occupation policy was not qualitatively different from that of the American and Soviet occupation forces, it was just carried out on a smaller scale. In order to put pressure on Bopp to evacuate the KWIP to France, the French Naval Commission imprisoned him for five days and threatened him with further imprisonment if he did not cooperate in the evacuation. During his imprisonment, the spectroscopist Hermann Schüler, who had a better relationship with the French, persuaded the French to appoint him as Deputy Director of the KWIP. This incident caused tension between the physicists and spectroscopists at the KWIP and within its umbrella organization the Kaiser-Wilhelm Gesellschaft (Kaiser Wilhelm Society).

Soviet
At the close of World War II, the Soviet Union had special search teams operating in Austria and Germany, especially in Berlin, to identify and "requisition" equipment, material, intellectual property, and personnel useful to the Soviet atomic bomb project. The exploitation teams were under the Soviet Alsos and they were headed by Lavrentij Beria's deputy, Colonel General A. P. Zavenyagin. These teams were composed of scientific staff members, in NKVD officer's uniforms, from the bomb project's only laboratory, Laboratory No. 2, in Moscow, and included Yulij Borisovich Khariton, Isaak Konstantinovich Kikoin, and Lev Andreevich Artsimovich. Georgij Nikolaevich Flerov had arrived earlier, although Kikoin did not recall a vanguard group. Targets on the top of their list were the Kaiser-Wilhelm Institut für Physik (KWIP, Kaiser Wilhelm Institute for Physics), the Frederick William University (today, the University of Berlin), and the Technische Hochschule Berlin (today, the Technische Universität Berlin (Technical University of Berlin'').

German physicists who worked on the Uranverein and were sent to the Soviet Union to work on the Soviet atomic bomb project included: Werner Czulius, Robert Döpel, Walter Herrmann, Heinz Pose, Ernst Rexer, Nikolaus Riehl, and Karl Zimmer. Günter Wirths, while not a member of the Uranverein, worked for Riehl at the Auergesellschaft on reactor-grade uranium production and was also sent to the Soviet Union.

Zimmer's path to work on the Soviet atomic bomb project was through a prisoner of war camp in Krasnogorsk, as was that of his colleagues Hans-Joachim Born and Alexander Catsch from the Kaiser-Wilhelm Institut für Hirnforschung (KWIH, Kaiser Wilhelm Institute for Brain Research, today the Max-Planck Institut für Hirnforschung), who worked there for N. V. Timofeev-Resovskij, director of the Abteilung für Experimentelle Genetik (Department of Experimental Genetics). All four eventually worked for Riehl in the Soviet Union at Laboratory B in Sungul'.

Von Ardenne, who had worked on isotope separation for the Reichspostministerium (Reich Postal Ministry), was also sent to the Soviet Union to work on their atomic bomb project, along with Gustav Hertz, Nobel laureate and director of Research Laboratory II at Siemens, Peter Adolf Thiessen, director of the Kaiser-Wilhelm Institut für physikalische Chemie und Elektrochemie (KWIPC, Kaiser Wilhelm Institute for Chemistry and Electrochemisty, today the Fritz Haber Institute of the Max-Planck Society), and Max Volmer, director of the Physical Chemistry Institute at the Berlin Technische Hochschule (Technical University of Berlin), who all had made a pact that whoever first made contact with the Soviets would speak for the rest. Before the end of World War II, Thiessen, a member of the Nazi Party, had Communist contacts. On 27 April 1945, Thiessen arrived at von Ardenne's institute in an armored vehicle with a major of the Soviet Army, who was also a leading Soviet chemist, and they issued Ardenne a protective letter (Schutzbrief).

Comparison of the Manhattan Project and the Uranverein
The joint American, British, and Canadian Manhattan Project developed the uranium and plutonium atomic bombs. Its success is attributable to meeting all four of the following conditions:


 * 1) A strong initial drive, by a small group of scientists, to launch the project.
 * 2) Unconditional government support from a certain point in time.
 * 3) Essentially unlimited manpower and industrial resources.
 * 4) A concentration of brilliant scientists devoted to the project.

Even with all four of these conditions in place the Manhattan Project succeeded only after the war in Europe had been brought to a conclusion. Mutual distrust existed between the German government and some scientists.

For the Manhattan Project, the second condition was met on 9 October 1941 or shortly thereafter. Germany fell short of what was required to make an atomic bomb. By the end of 1941 it was already apparent that the German nuclear weapon project would not make a decisive contribution to ending the German war effort in the near term, and control of the project was relinquished by the Heereswaffenamt (HWA, Army Ordnance Office) to the Reichsforschungsrat (RFR, Reich Research Council) in July 1942.

As to condition four, the high priority allocated to the Manhattan Project allowed for the recruitment and concentration of capable scientists on the project. In Germany, on the other hand, a great many young scientists and technicians who would have been of great use to such a project were conscripted into the German armed forces, while others had fled the country before the war due to antisemitism and political persecution.

Whereas Enrico Fermi, a scientific Manhattan leader, had a "unique double aptitude for theoretical and experimental work" in the 20th century, the successes at Leipzig until 1942 resulted from the cooperation between the theoretical physicist Werner Heisenberg and the experimentalist Robert Döpel. Most important was their experimental proof of an effective neutron increase in April 1942. At the end of July of the same year, the group around Fermi also succeeded in the neutron increase within a reactor-like arrangement.

In June 1942, Döpels "Uran-Maschine" was destroyed by a chemical explosion introduced by hydrogen, which finished the work on this topic at Leipzig. Thereafter, despite increased expenditures the Berlin groups and their extern branches didn't succeed in getting a reactor critical until the end of World War II. However, this was realized by the Fermi group in December 1942, so that the German advantage was definitively lost, even with respect to research on energy production.

Controversies regarding alleged nuclear tests
David Irving's 1967 book The Virus House claimed that some of Diebner's researchers had unsuccessfully attempted to produce fusion using conventional explosives and heavy paraffin as a deuterium carrier. Irving also describes an experiment in 1943 carried out by Trinks and Sachsse, which used a hollow sphere of silver filled with deuterium, imploded by conventional explosives. Again it was unsuccessful, no trace of radioactivity being produced.

A 2005 book by Rainer Karlsch, Hitlers Bombe claimed to have located, in the archives of the former KGB in Moscow, Heisenberg's speech notes from the Harnack Haus conference of July 1942, revealing that Heisenberg was a strong advocate for development of a Nazi nuclear weapon.

Karlsch alleged that Diebner's team conducted the first successful nuclear weapon test of some type (employing hollow charges for ignition) of nuclear-related device in Ohrdruf, Thuringia on 4 March 1945. Karlsch quoted a purported eyewitness named Clare Werner, who claimed to have been standing on a hillside in Thuringia at the time of the test:

"Not too far away was the military training base near the town of Ohrdruf. Unexpectedly there was a flash of light. 'I suddenly saw something,' she said ... 'it was as bright as hundreds of bolts of lightning, red on the inside and yellow on the outside, so bright you could've read the newspaper. It all happened so quickly, and then we couldn't see anything at all. We just noticed there was a powerful wind ...'"

However, Karlsch himself has acknowledged that he lacked absolute proof for the claims made in his book.

Science historian Mark Walker also published his analysis in 2005. In 2005 Karlsch and Walker published an article on the controversial historical evidence. In 2006 the Physikalisch-Technische Bundesanstalt (PTB; "Federal Institute for Physics Technology") concluded tests of soil samples from the area of the alleged test, summarizing the results in the phrase kein Befund ("nothing found").

In 2007, Karlsch, with Heinko Petermann, published a sequel to Hitler's Bombe, elaborating on issues raised in his first book: ''Für und Wider "Hitlers Bombe" (Münster; Waxmann).