Comment by hanslub42

In 1942, Heisenberg became the director of the Kaiser Wilhelm Institute for Theoretical Phiysics, where research into nuclear physics was conducted (on a small scale) and a Uranmaschine (small experimental reactor) was built. At that point, Heisenberg indeed didn't believe anymore in the possibility of building a fission bomb. But a year before that, Heisenberg had told Niels Bohr that he believed that such a weapon was possible. So, you're right: although there was an "atomic weapons program" in Germany, it became an "atomic energy program" quite early on, and that happened before Heisenberg became a leading figure in it. The Allies came to know this only after 1945.