Little Boy

"Little Boy" was the codename for the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon. The second, the "Fat Man", was dropped three days later on Nagasaki.

The weapon was developed by the Manhattan Project during World War II. It derived its explosive power from the nuclear fission of uranium 235. The Hiroshima bombing was the second artificial nuclear explosion in history, after the Trinity test, and the first uranium-based detonation. Approximately 600 to 860 milligrams of matter in the bomb was converted into the active energy of heat and radiation (see mass-energy equivalence for detail). It exploded with an energy of 16 kilotons of TNT (67 TJ). It has been estimated that 130,000 to 150,000 people had died as a result of its use by the end of December 1945. Its design was not tested in advance, unlike the more complex plutonium bomb (Fat Man). The available supply of enriched uranium was very small at that time, and it was felt that the simple design of a uranium "gun" type bomb was so sure to work that there was no need to test it at full scale.