The United States first began developing nuclear weapons during World War II under the order of President Franklin Roosevelt in 1939, motivated by the fear that they were engaged in a race with Nazi Germany to develop such a weapon. After a slow start under the direction of the National Bureau of Standards, at the urging of British scientists and American administrators, the program was put under the Office of Scientific Research and Development, and in 1942 it was officially transferred under the auspices of the United States Army and became known as the Manhattan Project, an American, British and Canadian joint venture. Under the direction of General Leslie Groves, over thirty different sites were constructed for the research, production, and testing of components related to bomb-making. These included the Los Alamos National Laboratory at Los Alamos, New Mexico, under the direction of physicist Robert Oppenheimer, the Hanford plutonium production facility in Washington, and the Y-12 National Security Complex in Tennessee.