Bradbury Science Museum. Replicas of the nuclear weapons dropped on Japan at the end of the Second World War, at the Bradbury Science Museum, Los Alamos National Laboratory, New Mexico, USA. The Los Alamos National Laboratory was the site where the world's first atomic bomb was developed as part of the Manhattan Project. The bomb was detonated by the US Army on 16th July 1945. The bomb dropped on Hiroshima on 6th August 1945 was a gun-type weapon (green) code-named 'Little Boy', whereas that dropped on Nagasaki three days later was an implosion-type (yellow), code-named 'Fat Man'.