Nuclear weapons were developed during World War II by the Manhattan Project, a major research and development effort led by the United States, with participation from the United Kingdom and Canada. From 1942 to 1946, it was under the direction of Major General Leslie R. Groves, Jr., of the US Army Corps of Engineers. It created a network of production facilities, most notably for uranium enrichment at Oak Ridge, Tennessee, plutonium production at Hanford, Washington and weapons research and design at the Los Alamos Laboratory in Los Alamos, New Mexico.