"Fat Man" atomic bomb
A "Fat Man" bomb was dropped over Nagasaki, Japan, on Aug. 9, 1945, near the end of World War II. Released by the B-29 Bockscar, the 10,000-pound weapon was detonated at an altitude of approximately 1,800 feet over the city. The bomb had an explosive force (yield) of about 20,000 tons of TNT, about the same as the bomb dropped on Hiroshima. Because of Nagasaki's hilly terrain, however, the damage was somewhat less extensive than of the relatively flat Hiroshima.
"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.