The world's first atomic bomb used in combat, like the one pictured above , looked like an elongated trash can with fins. It was ten feet long and weighed almost 9,000 pounds. This explosion-type uranium bomb, Little Boy, was considerably less complicated in design than the plutonium Fat Man implosion weapon. Unlike Fat Man, Little Boy was armed prior to flight. Little Boy was relatively easy to detonate, using a standard explosion trigger, called the "gun" method. The firing mechanism was so simple that the chance of failure was calculated to be only one in ten thousand.

The world's second atomic bomb used in combat, like the one pictured above , looked like a large pumpkin with fins. The implosion-type plutonium bomb was named Fat Man after Great Britain's Prime Minister, Winston Churchill. It was 12 feet long and weighed 10,000 pounds. The complicated electrical and detonation systems were packed into the front and rear pockets of the pumpkin-like shell. A small removable panel on the side permitted the bomb to be "armed" while in flight(Van Til,p. 263).