Weighing about 9,000 pounds, it produced an explosive force equal to 20,000 tons of TNT. The result of the Manhattan Project, begun in June 1942, 'Little Boy' was a gun-type weapon, which detonated by firing one mass of uranium down a cylinder into another mass to create a self-sustaining nuclear reaction. It was delivered by the B-29 Enola Gay (on display at the Smithsonian National Air & Space Museum), it detonated at an altitude of 1,800 feet over Hiroshima, Japan, on Aug.
The Mk I bomb, nicknamed 'Little Boy,' was the first nuclear weapon used in warfare.
