On June 17, 1942, President Roosevelt approved the report recommending the creation of the project, soon to be known as the Manhattan Engineer District. On September 19th, 1942, the Oak Ridge site, named the Clinton Engineer Works, was chosen to produce the materials which would be used to fuel a nuclear weapon. Two months following the site selection, construction began to create the material, enriched uranium, and to create a city to support those workers and their families who came to this East Tennessee area to help end World War II.
Planners initially envisioned a population of 13,000. Within a few months, project plant operators and city planners were raising their estimates to 42,000 and then to 62,000. The City of Oak Ridge grew to a population of around 75,000 by the summer of 1945. By December 1946, the population had dropped to 42,465. The Manhattan Engineer District implemented plans to develop and provide the necessary housing, commercial, utility, school and medical facilities to recruit and retain the highly specialized personnel required for construction and operation of the industrial plants.1
The four main plants: X-10 (Graphite Reactor), Y-12 (Electromagnetic Separation), K-25 (Gaseous Diffusion), and S-50 (Liquid Thermal Diffusion) were constructed from 1943 to 1945.