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Little Boy
Little Boy was the codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 by the Boeing B-29 Superfortress ''Enola Gay'', piloted by Colonel Paul W. Tibbets, Jr., commander of the 509th Composite Group of the United States Army Air Forces. It was the first atomic bomb to be used in warfare. The Hiroshima bombing was the second artificial nuclear explosion in history, after the Trinity test, and the first uranium-based detonation. It exploded with an energy of approximately . The bomb caused significant destruction to the city of Hiroshima.
Little Boy was developed by Lieutenant Commander Francis Birch's group of Captain William S. Parsons's Ordnance (O) Division at the Manhattan Project's Los Alamos Laboratory during World War II. Parsons flew on the Hiroshima mission as weaponeer. The Little Boy was a development of the unsuccessful Thin Man nuclear bomb. Like Thin Man, it was a gun-type fission weapon, but derived its explosive power from the nuclear fission of uranium-235. This was accomplished by shooting a hollow cylinder of uranium over another hollow enriched uranium cylinder by means of a charge of nitrocellulose propellant powder. It contained of enriched uranium, of which less than a kilogram underwent nuclear fission. Its components were fabricated at three different plants so that no one would have a copy of the complete design.
After 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, but by mid-1946 the Hanford Site reactors were suffering badly from the Wigner effect, so six Little Boy assemblies were produced at Sandia Base. The Navy Bureau of Ordnance built another 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft. All the Little Boy units were withdrawn from service by the end of January 1951.
==Naming==
The names for all three atomic bomb design projects during World War II—Fat Man, Thin Man, and Little Boy—were created by Robert Serber, a former student of Los Alamos Laboratory director Robert Oppenheimer who worked on the Manhattan Project. According to Serber, he chose them based on their design shapes. The "Thin Man" was a long device, and the name came from the Dashiell Hammett detective novel and series of movies by the same name. The "Fat Man" was round and fat, and was named after Sydney Greenstreet's "Kasper Gutman" character in ''The Maltese Falcon''. Little Boy would come last and was named after Elisha Cook, Jr.'s character in the same film, as referred to by Humphrey Bogart.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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