The Manhattan Project was first formalized on October 9, 1941 by order of President Roosevelt. After significant work, the Trinity device was successfully tested on July 16, 1945. This proof of concept led to manufacturing of at least two atomic bombs that were used in the destruction of Hiroshima and Nagasaki in August 1945.
The origins of the Manhattan Project came after a number of European physicists who had fled to the United States wrote a joint letter to President Roosevelt warning that Nazi Germany was attempting to develop an atomic bomb. The Manhattan District began work in earnest on August 13, 1942 at more than 30 facilities around the country. The sites of the Manhattan Project included laboratories at the University of California - Berkeley and the University of Chicago, the Army Engineering Works at Los Alamos, New Mexico and Oak Ridge, Tennessee, as well as other component manufacturers and refinement facilities in the United States and Canada.
Los Alamos also served as the de facto headquarters of the project under the administration of Major General Leslie Groves of the Army Corps of Engineers and Robert Oppenheimer, the director of the Los Alamos National Laboratory. The latter was a key figure in guiding the design of the atomic bomb, working with Nobel Prize-winning physicists from around the world in the race to develop the device.