After the first plutonium bomb was tested at Trinity Site, the next available weapon was the completed Little Boy. Dropped on Hiroshima, Japan on the morning of August 6, 1945, Little Boy was the first nuclear weapon used in warfare. Fat Man was the second and last nuclear weapon used in warfare. It was dropped on Nagasaki, Japan on August 9, 1945. While Little Boy was a uranium gun-type device, Fat Man was a more complicated and powerful implosion weapon using plutonium, similar to the device tested at Trinity. A subcritical sphere of plutonium was placed in the center of a hollow sphere of high explosive. Numerous detonators located on the surface of the high explosive 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.