Little Boy

LIttle Boy Bomb awaiting to be loaded into the Enola Gay

The Little Boy bomb in the bomb pit, ready for loading into the Enola Gay.

In essence, the Little Boy design consisted of a gun that fired one mass of uranium 235 at another mass of uranium 235, thus creating a supercritical mass. A crucial requirement was that the pieces be brought together in a time shorter than the time between spontaneous fissions. Once the two pieces of uranium are brought together, the initiator introduces a burst of neutrons and the chain reaction begins, continuing until the energy released becomes so great that the bomb simply blows itself apart.

Little Boy Specifications

Length: 120.0 inches (10 feet / 3.0 meters)
Diameter: 28.0 inches (71.1 cm)
Weight: 9,700 lbs (4,400 kg)
Yield: 15 kiltons (+/- 20%)