Fat Man Being Readied

The rapid spontaneous fission rate of plutonium 239 necessitated that a different type of bomb be designed. A gun-type bomb would not be fast enough to work. Before the bomb could be assembled, a few stray neutrons would have been emitted, and these would start a premature chain reaction­leading to a great reduction in the energy released.

Fat Man Specifications

Length:	128.375 inches (10 feet 8 inches / 3.25 meters)
Diameter:	60.25 inches (5 feet / 1.5 meters)
Weight:	10,265 lbs (4,656 kg)
Yield:	21 kilotons (+/- 10%)