Most people would prefer that the atomic bomb had not been invented. But in 1940, with Germany at war with the world and possibly working on a bomb of its own, the development of an atomic weapon seemed essential. US physicist Robert Oppenheimer took charge of the Manhattan project, which developed the technology needed to purify the right kind of uranium or plutonium and make it explode. After a test in july 1945, the first atomic bomb used in war was dropped on 6 August, destroying the Japanese city of Hiroshima and most of its inhabitants.