Between 1941 and 1945, scientists at Oak Ridge, Tennessee, led by Robert Oppenheimer, worked on the Manhattan Project to make an atomic bomb. On 16 July 1945, the atomic bomb was successfully tested at Alamogordo, in New Mexico.
The decision whether to drop it – almost as difficult as making the bomb – was taken by US President Harry S Truman. One reason Truman is said to have dropped the atomic bomb was to bring the war against Japan to a quick end. He said it was dropped to save American soldiers' lives. Some historians suspect Truman did not want to give the Soviets a chance to get involved in the Far East. Others feel that he was forced into a show of strength because of the threat to America posed by the USSR.
On 6 August 1945 the first atomic bomb, codenamed 'Little Boy', was dropped on the Japanese city of Hiroshima. Three days later, a second bomb was dropped on Nagasaki.
On 14 August 1945, the Japanese surrendered.
The creation and use of the atomic bomb was truly a turning point in warfare. The atomic bomb changed international relations. The superpowers of the USA and the USSR did not dare to start a war where both sides had nuclear weapons.