Little Boy was the code name of the uranium atomic bomb dropped on Hiroshima in 1945.
The United States used Little Boy in the first atomic attack in warfare on August 6, 1945. The bomb was carried by the B-29 Enola Gay and detonated over Hiroshima after being released at approximately 8:15 a.m. local time.
Little Boy used a gun-type fission design based on uranium-235. This design was considered sufficiently reliable that it did not require a full-scale test before combat use.
The second wartime atomic bomb, dropped on Nagasaki on August 9, was called Fat Man and used a different plutonium-based implosion design. Thin Man was an earlier project name for a proposed plutonium gun-type weapon, while Pumpkin referred to a conventional bomb used in testing and training missions.