The names of the two atomic bombs dropped on Japan were "Little Boy" and "Fat Man". Little Boy was the code name for the atomic bomb dropped on the city of Hiroshima on August 6, 1945. It was a uranium-based implosion-type weapon with an estimated yield of 13 to 18 kilotons of TNT. Fat Man was the code name for the atomic bomb dropped on the city of Nagasaki on August 9, 1945. It was a plutonium-based implosion-type weapon with an estimated yield of 21 kilotons of TNT.