The United States used two atomic bombs against Japan in August 1945.
The first, Little Boy, was dropped on Hiroshima on August 6, 1945. The second, Fat Man, was dropped on Nagasaki on August 9. These attacks were the first and remain the only uses of nuclear weapons in an armed conflict.
The two bombs used different designs. Little Boy was a uranium gun-type weapon, while Fat Man was a more complex plutonium implosion weapon. The Manhattan Project had produced both weapons under extraordinary wartime secrecy, with facilities and personnel spread across the United States and Canada.
The bombings occurred alongside other decisive events, including the Soviet Union’s entry into the war against Japan on August 8–9 and the Japanese government’s struggle over whether to accept the Potsdam terms. Japan announced surrender on August 15, followed by the formal signing on September 2.