The atomic bomb dropped on Nagasaki on August 9, 1945, was nicknamed Fat Man.
A B-29 bomber named Bockscar delivered Fat Man over Nagasaki three days after Little Boy was used against Hiroshima. Fat Man was a plutonium implosion-type weapon, making its internal design different from Hiroshima’s uranium gun-type bomb.
The intended primary target was Kokura, but cloud cover and smoke prevented the crew from making the required visual attack. The aircraft therefore proceeded to its secondary target, Nagasaki, where the bomb was released.
Fat Man and Little Boy are often mixed up because they were both American atomic weapons used in Japan. Their names, target cities, dates, and technical designs were different. Japan announced its surrender six days after the Nagasaki bombing.