It all started on December 7 1941 when the Japanese attacked Pearl Harbor and U.S forces began war with the Japanese. On August 6, 1945, during World War 2 (1939-45) and American B-29 bomber dropped the world's first deployed atomic bomb over the Japanese city of Hiroshima killing almost 100,000 people instantly. Three days later a second American bomber dropped another atomic bomb on Nagasaki, killing an estimated 40,000 people on top of those killed in Hiroshima. To this day the bombings remain the only use of nuclear weaponry for warfare.