The atomic bombings of Hiroshima and Nagasaki were nuclear attacks during World War II against the Empire of Japan by the United States of America under US President Harry S. Truman. On August 6, 1945, the nuclear weapon "Little Boy" was dropped on the city of Hiroshima, followed on August 9, 1945 by the detonation of the "Fat Man" nuclear bomb over Nagasaki. They are the only instances of the use of nuclear weapons in warfare.

http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki