Quoted from Wikipedia . . .
Oak Ridge was established in the early 1940s as a base for the Manhattan Project— the massive U.S. government operation that developed the atomic bomb. As such, scientific development still plays a crucial role in the city's economy and culture in general.
In 1942, the United States Federal Government chose the area as a site for developing materials for the Manhattan Project. Maj. Gen. Leslie Groves, military head of the Manhattan Project, liked the area for several reasons. Its relatively low population made acquisition affordable, yet the area was accessible by both highway and rail, and utilities such as water and electricity were readily available due to the recent completion of Norris Dam. With Tennessee's history as a right-to-work state, Union rules or civilian wage issues were virtually non-existent. Finally, the project location was established within a 17-mile (27-km) long valley, and the valley itself was linear and partitioned by several ridges, providing natural protection against disasters between the four major industrial plants -- so they wouldn't blow up "like firecrackers on a string".The location and low population also helped keep the town a secret. Although the population of the settlement grew from about 3,000 in 1942 to about 75,000 in 1945, and despite the fact that the K-25 uranium-separating facility by itself covered 44 acres (178,000 m²) and was the largest building in the world at that time, Oak Ridge was kept an official government secret. It did not appear on maps, and wasn't formally named until 1949, only being referred to as the Clinton Engineering Works (CEW). All workers wore badges, and the town was surrounded by guard towers and a fence with seven gates.