Operation Alsos

This theory centers on one man in particular, Samuel Abraham Goudsmit (1902-1978). Goudsmit was a nuclear physicist who headed Operation Alsos as a branch off the Manhattan Project. While America considered it vitally important to beat the Nazis at making the atomic bomb, they found it equally important to hinder the Germans as far as possible.
The Allied war effort saw to that magnificently by bombing Nazi ball bearing plants. Hardly any machinery in the world functioned without ball bearings, and while the Nazis attempted to research nuclear physics, Goudsmit organized a spy ring to report on how close the Germans were coming to the bomb. His published reports stated that they never got close, but the truth, according to this conspiracy theory, is much more insidious.
Goudsmit is said to have discovered that the Nazi nuclear physicists, led by Otto Hahn and Werner Heisenberg, actually built the bomb, or at least discovered all the technology involved in building one and were in the process of doing so, which Hitler intended to use on London, England. In order to counter this, Goudsmit informed the U. S. Government, which found it more promising to buy the Nazi scientists off than to carpet bomb the areas where nuclear testing was occurring. Additionally, Goudsmit had been unable to ascertain from the scientists where this testing was being done. After the War, laboratories were discovered all over Germany, which means bombing would not have been feasible.
So Goudsmit was given millions of dollars to bribe the Nazi scientists into coming to America, with the bomb and all research and materiel, and those scientists partnered with Robert Oppenheimer, Enrico Fermi, and Edward Teller, and enabled the Americans to finish their fission research, then build bombs. The Trinity Test of 16 July 1945 is claimed by this theory to have been the original Nazi bomb.