What was the U.S. atomic bomb dropped on Hiroshima called in 1945?

Little Boy was the U.S. atomic bomb dropped on Hiroshima on August 6, 1945.

The weapon was a uranium-235 gun-type fission bomb carried by the B-29 bomber Enola Gay. It detonated over Hiroshima at approximately 8:15 a.m. Japan Standard Time, producing catastrophic blast, heat, and radiation effects.

Little Boy was the first nuclear weapon used in combat. It had not been tested before the Hiroshima mission because its gun-type design was considered sufficiently predictable. The weapon’s explosive yield is commonly estimated at about 15 kilotons of TNT, although wartime and later estimates varied.

A frequent mix-up is the identity of the two bombs used against Japan. Little Boy was used against Hiroshima, while Fat Man, a plutonium implosion weapon, was used against Nagasaki three days later. Japan announced its acceptance of the Allied surrender terms on August 15, after both bombings and the Soviet entry into the war against Japan.