Which country first used an atomic bomb in warfare?

The United States first used an atomic bomb in warfare.

The United States dropped a uranium bomb called Little Boy on Hiroshima, Japan, on 6 August 1945. Three days later, it dropped the plutonium bomb Fat Man on Nagasaki. These remain the only wartime uses of nuclear weapons.

The attacks occurred near the end of World War II, while Japan was still fighting the Allied powers. Japan announced its surrender on 15 August 1945, and the surrender document was signed on 2 September. The bombings caused enormous loss of life, both immediately and from later injuries and radiation effects.

The weapons were developed through the Manhattan Project, a secret wartime program involving American, British, and Canadian scientists. The Soviet Union tested its first atomic bomb in 1949, ending the United States' brief nuclear monopoly.