"Fat Man" was an implosion-type weapon using plutonium. A subcritical sphere of plutonium was placed in the center of a hollow sphere of high explosive (HE). Numerous detonators located on the surface of the HE were fired simultaneously to produce a powerful inward pressure on the capsule, squeezing it and increasing its density. This resulted in a supercritical condition and a nuclear explosion.
Fat Man
Atomic Bomb
Fat Man was dropped by the B-29 Bockscar over Nagasaki, Japan, on August 9, 1945, ending World War II. It detonated at approximately 1,800 feet over the city and had a yield equal to about 20,000 tons of TNT, about the same as the bomb dropped on Hiroshima.