The National Museum of Nuclear Science & History: Fat Man (yellow) and Little Boy (green).

On July 16, 1945, the Fat Man prototype was tested in the New Mexico desert site code named Trinity. Thus, the Atomic Age began. Dropped on Nagasaki, Japan on August 9, 1945, Fat Man was the second, and last nuclear weapon used in warfare. Little Boy was the first. It exploded approximately 1800 feet over Hiroshima, Japan on the morning of August 6, 1945. Unlike the Fat Man plutonium weapon, Little Boy was not tested prior to use in Japan.

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