Invitation to a party at the Los Alamos laboratory, 1945. This invitation was issued by the British Mission, the group of British scientists who joined the Los Alamos laboratory in New Mexico, USA, in 1942-45. Los Alamos was one of the key sites of the Manhattan Project, the American effort to design and build the world's first atomic bombs. Two types of bombs were made, a uranium bomb and a plutonium bomb. They were dropped on Hiroshima and Nagasaki in August 1945, ending World War 2. This party for The Birth of the Atomic Era" was held some 6 weeks later."