As the first design developed (as well as the first deployed for combat), it is sometimes known as the Mark I. All the Little Boy units were withdrawn from service by the end of January 1951.īecause uranium-235 was known to be fissionable, it was the first material pursued in the approach to bomb development. The Navy Bureau of Ordnance built another 25 Little Boy assemblies in 1947 for use by the Lockheed P2V Neptune nuclear strike aircraft which could be launched from the Midway-class aircraft carriers. However, by mid-1946, the Hanford Site reactors began suffering badly from the Wigner effect, the dislocation of atoms in a solid caused by neutron radiation, and plutonium became scarce, so six Little Boy assemblies were produced at Sandia Base. Its components were fabricated at three different plants so that no one would have a copy of the complete design.Īfter the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed. It contained 64 kg (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. Like Thin Man, it was a gun-type fission weapon, but it derived its explosive power from the nuclear fission of uranium-235, whereas Thin Man was based on fission of plutonium-239. 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 unsuccessful Thin Man nuclear bomb. The Hiroshima bombing was the second man-made 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 of the United States Army Air Forces and Captain Robert A. The bomb was dropped by the Boeing B-29 Superfortress Enola Gay piloted by Colonel Paul W. It was the first nuclear weapon used in warfare. " Little Boy" was the codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II.