During World War II, more migration west occurred because of war-related industries in California. US 66, already popular and fully paved, became one of the main routes and also served for moving military equipment. Fort Leonard Wood in Missouri was located near the highway, which was locally upgraded quickly to a divided highway to help with military traffic. When Richard Feynman was working on the Manhattan Project at Los Alamos, he used to travel nearly to visit his wife, who was dying of tuberculosis, in a sanatorium located on US 66 in Albuquerque.