Figure 1
The bomb dropped on Nagasaki (a) was a plutonium fission device, while the Hiroshima bomb (b) used uranium-235 fission. The nuclear bomb built and tested by members of Germany's uranium project (c) was designed to be a hybrid fission/fusion device. Neutrons released during fusion reactions between deuterium and tritium in the centre of the device would trigger fission reactions in the surrounding plutonium or highly enriched uranium.