What were the atomic bombings of Hiroshima and Nagasaki?

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The atomic bombings of Hiroshima and Nagasaki were American bombing raids on the Japanese cities of Hiroshima and Nagasaki during World War II, which marked the first use of atomic weapons in war. Little Boy, the bomb dropped on Hiroshima, was a gun-assembly fission bomb using uranium, whereas Fat Man, the bomb dropped on Nagasaki, was an implosion fission bomb utilizing plutonium.