text: The first successful man-made fusion device was the boosted fission weapon tested in 1951 in the Greenhouse Item test. The first true fusion weapon was 1952s Ivy Mike, and the first practical example was 1954s Castle Bravo. In these devices, the energy released by a fission explosion compresses and heats the fuel, starting a fusion reaction. Fusion releases neutrons. These neutrons hit the surrounding fission fuel, causing the atoms to split apart much faster than normal fission processes. This increased the effectiveness of bombs: normal fission weapons blow themselves apart before all their fuel is used; fusion/fission weapons do not waste their fuel.