The Clinton Engineer Works (CEW) was the production installation of the Manhattan Project that during World War II produced the enriched uranium used in the 1945 bombing of Hiroshima, as well as the first examples of reactor-produced plutonium. It consisted of production facilities arranged at three major sites, various utilities including a power plant, and the town of Oak Ridge. It was in East Tennessee, about west of Knoxville, and was named after the town of Clinton, to the north. The production facilities were mainly in Roane County, and the northern part of the site was in Anderson County. The Manhattan District Engineer, Kenneth Nichols, moved the Manhattan District headquarters from Manhattan to Oak Ridge in August 1943. During the war, CEW's advanced research was managed for the government by the University of Chicago.

Construction workers were housed in a community known as Happy Valley. Built by the Army Corps of Engineers in 1943, this temporary community housed 15,000 people. The township of Oak Ridge was established to house the production staff. The operating force peaked at 50,000 workers just after the end of the war. The construction labor force peaked at 75,000, and the combined employment peak was 80,000. The town was developed by the federal government as a segregated community; Black Americans lived only in an area known as Gamble Valley, in government-built "hutments" (one-room shacks) on the south side of what is now Tuskegee Drive.

Site selection

In 1942, the Manhattan Project was attempting to construct the first atomic bombs. This would require production facilities, and by June 1942 the project had reached the stage where their construction could be contemplated. On 25 June, the Office of Scientific Research and Development (OSRD) S-1 Executive Committee deliberated on where they should be located. Brigadier General Wilhelm D. Styer recommended that the different manufacturing facilities be built at the same site in order to simplify security and construction. Such a site would require a substantial tract of land to accommodate both the facilities and housing for the thousands of workers. The plutonium processing plant needed to be from the site boundary and any other installation, in case radioactive fission products escaped. While security and safety concerns suggested a remote site, it still needed to be near sources of labor and accessible by road and rail transportation. A mild climate that allowed construction to proceed throughout the year was desirable. Terrain separated by ridges would reduce the impact of accidental explosions, but they could not be so steep as to complicate construction. The substratum needed to be firm enough to provide good foundations but not so rocky that it would hinder excavation work. It was estimated that the proposed plants would need access to 150,000 kW of electrical power and of water per minute. A War Department policy held that, as a rule, munitions facilities should not be located west of the Sierra or Cascade Ranges, east of the Appalachian Mountains, or within of the Canadian or Mexican borders.

Several sites were considered in the Tennessee Valley, two in the Chicago area, one near the Shasta Dam in California, and some in Washington state, where the Hanford Site was eventually established. An OSRD team had selected the Knoxville area in April 1942, and in May Arthur Compton, the director of the University of Chicago's Metallurgical Laboratory, had met with Gordon R. Clapp, the general manager of the Tennessee Valley Authority (TVA). The Chief Engineer of the Manhattan District (MED), Colonel James C. Marshall, asked Colonel Leslie R. Groves Jr. to undertake a study within the Army's Office of the Chief of Engineers. After receiving assurances that the TVA could supply the required quantity of electric power if given priority for procuring some needed equipment, Groves also concluded that the Knoxville area was suitable. The only voice of dissent at the 25 June meeting was Ernest O. Lawrence, who wanted the electromagnetic separation plant located much nearer to his Radiation Laboratory in California. The Shasta Dam area remained under consideration for the electromagnetic plant until September, by which time Lawrence had dropped his objection.

On 1 July, Marshall and his deputy, Lieutenant Colonel Kenneth Nichols, surveyed sites in the Knoxville area with representatives of the TVA and Stone & Webster, the designated construction contractor. No perfectly suitable site was found, and Marshall even ordered another survey of the Spokane, Washington area. At the time, the proposed nuclear reactor, gas centrifuge and gaseous diffusion technologies were still in the research stage, and the design of the plant was a long way off. The schedules—which called for construction work on the nuclear reactor to commence by 1 October 1942, the electromagnetic plant by 1 November, the centrifugal plant by 1 January 1943, and the gaseous diffusion plant by 1 March—were unrealistic. While work could not commence on the plants, a start could be made on the housing and administrative buildings. Stone & Webster therefore drew up a detailed report on the most promising site west of Knoxville. Stephane Groueff later wrote:

The site was located in Roane County and Anderson County and lay roughly halfway between the two county seats of Kingston and Clinton. Its greatest drawback was that a major road, Tennessee State Route 61, ran through it. Stone & Webster considered the possibility of re-routing the road. The Ohio River Division of the Corps of Engineers estimated that it would cost $4.25 million (equivalent to $ in ) to purchase the entire site.

Groves became the director of the Manhattan Project on 23 September, with the rank of brigadier general. That afternoon, he took a train to Knoxville, where he met with Marshall. After touring the site, Groves concluded that the site "was an even better choice than I had anticipated". He called Colonel John J. O'Brien of the Corps of Engineers' Real Estate Branch and told him to proceed with acquiring the land. The site was initially known as the Kingston Demolition Range; it officially became the Clinton Engineer Works (CEW) in January 1943 and was given the codename Site X. After the township was established in mid-1943, the name Oak Ridge was chosen from employee suggestions. The site met the Manhattan District's approval because "its rural connotation held outside curiosity to a minimum". Oak Ridge then became the site's postal address, but the site was not officially renamed Oak Ridge until 1947.

Land acquisition

Although War Department policy maintained that land should be acquired by direct purchase, time was short and thus it was decided to proceed immediately with condemnation. This allowed access to the site for construction crews, provided faster compensation to the owners, and expedited the handling of property with defective titles. On 28 September 1942, the ORD Real Estate Branch opened a project office in Harriman with a staff of 54 surveyors, appraisers, lawyers and office workers. The ORD Real Estate Branch was quite busy at this time, as it was also acquiring land for the Dale Hollow Reservoir, so some staff were borrowed from the Federal Land Bank and the TVA. The next day, Under Secretary of War Robert P. Patterson authorized the acquisition of at an estimated cost of $3.5 million (equivalent to $ in ). At the request of the ORD Real Estate Branch attorneys, the District Court for the Eastern District of Tennessee issued an order of possession on 6 October, effective the next day. Recognizing the hardship that it would cause to the landowners, it restricted immediate exclusive possession to properties "essential to full and complete development of the project".

Over 1,000 families lived on the site on farms or in the hamlets of Elza, Robertsville, and Scarboro. The first that most heard about the acquisition was when a representative from the ORD visited to inform them that their land was being acquired. Some returned home from work one day to find an eviction notice nailed to their door or to a tree in the yard. Most were given six weeks to leave, but some were given just two. The government took possession of 13 tracts for immediate construction work on 20 November 1942. By May 1943, 742 declarations had been filed covering . Most residents were told to prepare to leave between 1 December and 15 January. In cases where this would cause undue hardship, the MED allowed residents to stay beyond this date. For some it was the third time that they had been evicted by the government, having previously been evicted for the Great Smoky Mountains National Park in the 1920s and the TVA's Norris Dam in the 1930s. Many expected that, like the TVA, the Army would provide assistance to help them relocate; but unlike the TVA, the Army had no mission to improve the area or the lot of the local people, and thus no funds had been allocated for the purpose. Tires were in short supply in wartime America, and moving vehicles were difficult to find. Some residents had to leave behind possessions that they were unable to take with them.

A delegation of landowners presented the ORD Real Estate Branch with a petition protesting the acquisition of their property on 23 November 1942, and that night over 200 landowners held a meeting at which they agreed to hire lawyers and appraisers to challenge the federal government. Local newspapers and politicians were sympathetic to their cause. By the end of May 1943, agreements were reached covering 416 tracts totaling , but some landowners rejected the government's offers. The ORD Real Estate Branch invoked a procedure under Tennessee law that allowed for a jury of five citizens appointed by the federal district court to review the compensations offered. They handled five cases in which they proposed higher values than those of the ORD appraisers, but the landowners rejected them as well, so the Army discontinued the use of this method. In response to rising public criticism, O'Brien commissioned a review by the Department of Agriculture. It found that the appraisals had been fair and just, and that farmers had overestimated the size and productivity of their land.

The landowners turned to their local Congressman, John Jennings, Jr. On 1 February 1943, Jennings introduced a resolution in the House of Representatives calling for a committee to investigate the values offered to the landowners. He also complained to Patterson that buildings and facilities were being demolished by the MED. On 9 July, Andrew J. May, the chairman of the House Committee on Military Affairs, appointed an investigating subcommittee chaired by Tennessee Representative Clifford Davis, who selected Dewey Short of Missouri and John Sparkman of Alabama as its other members. Public hearings were held in Clinton on 11 August and in Kingston the following day. The committee report, presented in December 1943, made a number of specific recommendations concerning the Corps of Engineers' land acquisition process, but neither Congress nor the War Department moved to provide additional compensation for the landowners.