Little Boy was the first nuclear weapon used in warfare. It exploded approximately 1,800 feet over Hiroshima, Japan, with a force equal to 13,000 tons of TNT. Immediate deaths were between 70,000 to 130,000.
Fat Man was the second nuclear weapon used in warfare dropped on Nagasaki, Japan. Fat Man devastated more than two square miles of the city and caused approximately 45,000 immediate deaths.
While Little Boy was a uranium gun-type device, Fat Man was a more complicated and powerful plutonium implosion weapon that exploded with a force equal to 20,000 tons of TNT.
For little boy about 100kg of uranium 235 was needed.
For fat man only about 16 kg of Plutonium was needed.
