In 1940, Columbia University scientists led by John Dunning began research to beat Germany to the atomic bomb, but it took four years to learn how to make the very porous, strong barrier with holes tiny enough to separate uranium-235 from U-238 in the gaseous diffusion process. Because the diffusion step had to be repeated about 3,000 times to produce nearly pure U-235, the plant had to be enormous, covering 40 acres under one roof in a U shape with legs a half mile long, 400 feet wide, and four stories tall. Ground was broken in September 1943 for the $512 million K-25 plant, and despite its complexity and new technology, operation began in February 1945. The largest of any Manhattan Project facility, K-25 was built as a backup in case Y-12 did not succeed, but because its continuous process proved workable and far cheaper, it replaced Y-12 as the nation’s U-235 supplier. The Kellex Corporation led the design of the process and plant, the K-25 powerhouse built in 1944 was the largest steam generating station ever built at one time, and Carbide and Carbon Chemicals Corporation was the first plant operator. George T. Felbeck was Carbide’s general manager during the 1943-1944 building period, H.D. Kinsey during the 1945 startup year, and Clark E. Center in 1947, beginning a two-decade tenure. At the government’s urgent request in 1949, as the arms race began, K-25 personnel planned and oversaw a four-fold expansion of America’s U-235 production capacity, which later fueled peacetime nuclear power plants around the world.