During World War Two Nazi Germany had several competing nuclear projects many of which were infiltrated by a British intelligence operation based in Stockholm Sweeden known as Operation Epsilon.
Up until 1942 all nuclear research in Germany was controlled by the German Post Office Ministry. A meeting in 1942 pulled funding for research and ostensibly cancelled all efforts. What really happened was that a series of highly secret millitary projects spawned off it.
One by the German navy or Kreigsmarine concentrated on two concepts. Submersible Lafferenz capsules for V-2 rockets which were to be towed to near New York and the other for a nuclear powered version of the type XXI u-boat, which was the direct inspiration for the US Navy's nuclear submarines.
Another project spawned off was that of Dr Fritz Houtermanns who concentrated on designing a Plutonium bomb. This by implication relied upon the successful development of a nuclear reactor.
However the Kaiser Wilhelm Gesellschaft Intsitut fur Physiche (KWG) also maintained efforts at Dahlem near Berlin under Professor Werner Heisenberg to create a nuclear reactor. After the war Heisenberg's ignorance of the A-bomb mechanism was held up as proof that Nazi Germany lacked the capacity to develop one.
This however seems flawed reasoning when one considers some other elements of the puzzle. For example a rival project by the Heereswaffenamt (HWA) later taken over by the Waffen SS had ten times the funding for nuclear research in 1944 that Heisenberg's KWG enjoyed. This rival project concentrated on a uranium A-bomb.
This project was headed by Dr Kurt Diebner to design an A-bomb. Dr Paul Harteck on Diebner's team developed the Harteck process of uranium centrifuges to enrich uranium.
After the war the Harteck process has been copied for the nuclear projects of South Africa Pakistan and now Iran. This process mixed uranium oxide mined from Czechoslovakia with flouric acid and then flourine gas to create a gas compound spun and heated in centrifuges.
Many of the scientific developments of Germany's nuclear projects during WW2 are still under embargo until 2045.
What is known however, is that shortly after the 1944 July bomb plot against Hitler the Waffen SS took over the V-2 project and the HWA project of Peter Diebner.
Prof Werner von Braun's brother, Sigsmund von Braun (nee von Ostorp) was a diplomatic attache at the Vatican when German forces retreated from Rome. His brother Sigsmund negotiated on behalf of the Waffen SS for a discreet surrender to US forces, known as Operation Sunrise. Prof Werner von Braun secretly visited the US embassy at Lisbon Portugal in October 1944 with General Dornberger according to summaries of Farm Hall transcripts after the war. There von Braun negotiated with representatives of General Electric Corporation for the handover of all Nazi scientists to US forces.
Corroboration of this is that Hitler ordered the execution of all scientists on the V-2 project and the Heereswaffenamt project, yet the person ordered to do so, SS Lt Gen Dr Hans Kammler in effect secretly smuggled the scientists south to Bavaria for the ALSOS mission to "capture" them.
It may be surmised that the Nazis could have built an atomic bomb, but the political pragmatism of key Nazis saw the nuclear project traded for something else.
Principal Sources:
Overheard, by David Irving
Virus House, by David Irving
The Borman Brotherhood, by William Stevenson
Sunrise: The Secret Surrender, by Bradley F. Smith and Elena Agarossi.
Hitler's Uranium Club: The Secret Recordings at Farm Hall, by Jeremy Bernstein