A historical photo of the K-25 gas diffusion plant in Oak Ridge, Tennessee, during World War II, which was constructed to assist in creating and concealing the atomic bomb. Camouflaged under the “Manhattan District,” this district was established in 1942 with no geographical boundaries to keep the project under wraps. Instead, the Manhattan District had three primary project sites: Oak Ridge, Tennessee; Hanford, Washington; and Los Alamos, New Mexico. (U.S. Army Corps of Engineers photo)