History of Atom Bombs that were Dropped on Japan's Hiroshima & NagaSAki by US during World War II

The atom bombs that were dropped on Japan were code-named:
The Little Boy Bomb:
Dropped on the Japanese city of Hiroshima on August 6, 1945, it was the first nuclear weapon used in a war.
The Fat Man Bomb:
Dropped on the Japanese city of Nagasaki on August 9, 1945, it was the second nuclear weapon used in a war.

In the pic: At the National Atomic Energy Museum, Albuquerque, New Mexico, USA, representative weapon casings for the Little Boy and Fat Man type weapons are on display.