A plaque commemorating the epochal events of December 2, 1942 is mounted on a wall near the site where a team of scientists led by Enrico Fermi achieved what was to ensure America's lead in the race to develop an atomic bomb. It was in the squash courts beneath Stagg Field, a football field on the campus of the University of Chicago, that Chicago Pile-1, the first nuclear reactor, went critical for the first time. The "reactor" – a term coined ten years later – consisted of a roughly spherical pile of neutron-producing uranium pellets interspersed with graphite blocks to slow the reaction. Fermi described it as "a crude pile of black bricks and wooden timbers." While a group of 40 dignitaries looked on, a young scientist called George Weil removed the cadmium-coated control rods that served to absorb the neutrons in the reactor, one by one. As each rod was removed, neutron activity in the pile increased. At 3.25 pm the pile achieved the critical mass necessary for a self-sustaining reaction, and remained that way for 28 minutes. Arthur Compton, head of the Office of Scientific Research and Development's S-1 Uranium Committee (later the Manhattan Project) made a coded phone call to James Conant, chairman of the National Defense Research Committee, that brought news of the experiment's success, saying: "The Italian navigator (Fermi) has landed in the new world, the natives are friendly."

The plaque reads: "On December 2, 1942, Man achieved the first self-sustaining chain reactions and thereby initiated the controlled release of nuclear energy."

Photograph, Ed Westcott , US Federal Government, 14 August 1945. War Ends. Celebrations in Oak Ridge, Tennessee, August 1945, after the bombing of Hiroshima and Nagasaki ended World War II. Oak Ridge was one of ten sites in the US which was part of the Manhattan Project, the codename for a project conducted during World War II to develop the first atomic bomb. Workers at the the uranium-enrichment facilities, which covered more than 60,000 acres (243 km²) of several former farm communities in the Tennessee Valley area, were unaware of their role in providing the refined uranium needed to produce atomic bombs at Los Alamos. The site was so secret that even the governor of the state was not told that Oak Ridge was being built. At times, the Oak Ridge plants, which produced uranium-235, the uranium isotope from which Little Boy, the Hiroshima bomb, was made, were consuming one sixth of the electrical power produced in the U.S.