Little Boy contained 64 kilograms (141 lb) of highly enriched uranium, although less than a kilogram underwent nuclear fission. Fission was accomplished by shooting a hollow cylinder (the 'bullet') onto a solid cylinder of the same material (the 'target') by means of a charge of nitrocellulose propellant powder. It derived its explosive power from the nuclear fission of uranium-235, whereas Thin Man was based on fission of plutonium-239. Like Thin Man, it was a gun-type fission weapon. Little Boy was developed by Lieutenant Commander Francis Birch's group at the Manhattan Project's Los Alamos Laboratory during World War II, a reworking of their abandoned Thin Man nuclear bomb.
The Hiroshima bombing was the second nuclear explosion in history, after the Trinity nuclear test. It exploded with an energy of approximately 15 kilotons of TNT (63 TJ) and caused widespread death and destruction throughout the city.
Tibbets Jr., commander of the 509th Composite Group, and Captain Robert A. The bomb was dropped by the Boeing B-29 Superfortress Enola Gay piloted by Colonel Paul W. Little Boy was the name of the type of atomic bomb used in the bombing of the Japanese city of Hiroshima on 6 August 1945 during World War II, making it the first nuclear weapon used in warfare.
