Claim: Little Boy was the name for a bomb.

`` Little Boy '' was the codename for the atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II 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 15 ktonTNT . The bomb caused significant destruction to the city of Hiroshima and its occupants .   Little Boy was developed by Lieutenant Commander Francis Birch 's group of Captain William S. Parsons 's Ordnance -LRB- O -RRB- 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 enriched uranium -LRB- the `` bullet '' -RRB- onto a solid cylinder of the same material -LRB- the `` target '' -RRB- by means of a charge of nitrocellulose propellant powder . It contained 64 kg 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 Lockheed P2V Neptune nuclear strike aircraft -LRB- which could be launched from but not land on the Midway-class aircraft carriers -RRB- . All the Little Boy units were withdrawn from service by the end of January 1951 .