On February 18, 1943, construction began on the first building (9201-1) at the Y-12 Electromagnetic Separation Plant in Oak Ridge, TN. Y-12’s primary wartime purpose was to separate uranium 235 from uranium 238 for use in the world’s first atomic weapons. At the plant’s peak of operations in 1945, more than 22,000 workers including the famous Calutron Girls undertook this top-secret mission. On August 6, 1945, the US military dropped the Little Boy atomic bomb on Hiroshima, Japan, fueled by enriched uranium separated at Y-12.

Y-12’s nuclear research and development continued through the Cold War through the present day, where the complex remains a highly-secured facility operated for the US Department of Energy. https://www.nps.gov/mapr/index.htm