The United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki in August 1945, during the final stage of the Second World War.The two bombings, which killed at least 129,000 people, remain the only use of nuclear weapons for warfare in history.he release at 08:15 (Hiroshima time) went as planned, and the Little Boy containing about 64 kg (141 lb) of uranium-235 took 44.4 seconds to fall from the aircraft flying at about 31,000 feet (9,400 m) to a detonation height of about 1,900 feet (580 m) above the city.