little boy (bomb)
A uranium-infused atomic bomb developed by the United States as a part of the Manhattan Project. It was used during the Atomic Bombing of Hiroshima on 6 August, 1945, destroying the city in the process. Little Boy is the first nuclear weapon to ever be used in warfare.
Little Boy can be distinguished from its relative Fat Man by the more cylindrical shape of the bomb casing, as opposed to the more round shape of Fat Man's.