Starting with farmland in November 1942, 110,000 construction workers spent two-and-a-half years building the uranium-235 production plants Y-12 and K-25 at a cost of $759 million, X-10 and S-50 at a cost of $23 million, and the town where plant workers lived at a cost of $96 million. Gathering so many skilled and unskilled laborers at the height of World War II was extremely difficult because U.S. war work needed them everywhere, and construction union leaders and their organizations made major efforts to help the War Manpower Commission, U.S. Employment Service, and the Army find the thousands required. Oak Ridge's bus system grew into the ninth largest in the U.S., bringing in as many as 20,000 workers daily, including people from surrounding counties who could not find living quarters there. At K-25, where the construction work force neared 25,000 in May 1945, a complete town called Happy Valley was built at the work site for workers and their families, though it later disappeared. Peak construction employment came in April 1944, when 47,000 were building the plants and the town, which was rapidly growing into a city. By the war's end in August 1945, rushed construction in Oak Ridge had consumed 218 million man-hours, yet the rate of disabling injuries was only one-quarter that of the overall U.S. construction industry, an exceptional safety record.