Why did the Germans, the most advanced scientific nation, fail to build a nuclear bomb during the War? In late 1938 a Berlin scientist, Otto Hahn, discovered nuclear fission. Werner Heisenberg, the chief scientist of Germany's wartime nuclear project, pioneered quantum mechanics and won the Nobel Prize. When the Nazis came to power in 1933 Heisenberg friends begged him to leave Germany, knowing he would be asked to work on nuclear research for Hitler but he refused. The focus of the story is a famous meeting in Copenhagen in 1941 between Niels Bohr and Heisenberg where Heisenberg appealed to world physicists, via Bohr, to desist from or slow down nuclear research. But Hans Bethe, a contemporary of Heisenberg has another version of events.