In September 1942, U.S. Army Lt. Gen. Leslie Groves, commander of the Manhattan Project — the secret U.S. crash effort to develop the atomic bomb — faced a critical decision. The project needed to produce uranium-235, an isotope of uranium, whose unstable nucleus could be easily split to trigger a fission chain reaction and release an enormous amount of destructive energy. But that would require a massive, complex manufacturing process, involving tens of thousands of workers, which needed to be kept secret to thwart interference from spies and saboteurs. But, the question was, where could those facilities possibly be hidden?
As detailed in Charles W. Johnson's and Charles O. Jackson's 1981 book "City Behind a Fence: Oak Ridge Tennessee 1942-1946," U.S. officials already had identified potential sites in several parts of the country, but all of them had drawbacks. Shasta Dam in California, for example, was too close to the Pacific Coast, and thus vulnerable to an air attack, and several locations in Washington state would have required construction of long power lines to provide the massive amounts of electricity needed for the work. A site in Illinois near Chicago was out, as well. Officials didn't want to be close to a big population center, since the potential health risks of the work weren't clear, and it would have been easier for enemy agents to blend in.
So instead, Groves quickly settled upon a 52,000-acre (21,000-hectare) site in rural eastern Tennessee, later expanded to 59,000 acres (24,000 hectares). Not only would it be inconspicuous to anyone outside of the sparsely-populated area, but it also was close to hydroelectric plants operated by the Tennessee Valley Authority, which could supply the enormous amounts of electricity that the plants would require, according to Johnson's and Jackson's book. It was the perfect place to build both the Clinton Engineer Works, which would be the atomic complex, and a secret city to house the workers. The government decided to call the secret city Oak Ridge because it sounded "sufficiently bucolic and general to be used as a cover name for the residential area," as this 1969 article in a government publication explains.
Not long afterward, the U.S. government quietly started moving small farmers who had land on the site, paying them compensation but not telling them why, according to a 1945 article in The New Republic by Louis Falstein, one of the first reporters to write about Oak Ridge. Then came trainloads full of construction equipment and building materials. Construction crews quickly erected the buildings that would comprise the nondescriptly-named campus, as well as thousands of houses for scientists and workers. Many of the homes were B-1 Flat Tops, a design fashioned from prefabricated panels and roofing to save construction time.
Building and Recruiting
Building the secret industrial facilities and housing for workers cost around $1.32 billion (about $18.5 billion in today's dollars). That amounted to 60 percent of the Manhattan Project's total budget, according to D. Ray Smith, a retired historian for the Y-12 National Security Complex who also is the historian for the City of Oak Ridge and a columnist for the Oak Ridger, a local newspaper.
Over the next few years, Oak Ridge grew into a community of 75,000 people. "People came from all over the world," explains Smith. "Many of the scientists were Hungarians. A lot came out of Germany and Great Britain." Others were recruited for the Clinton Engineering Works by big U.S. companies working on the Manhattan Project, who scoured the campuses of U.S. colleges and universities for bright students with needed science and technical skills.
A young chemist named Bill Wilcox who was approached by an Eastman Kodak recruiter in 1943, for example, later recalled that he was only told that the job was some sort secret war work. "I asked where I'd be working," he said. "He wouldn't say — it was secret. I asked what sort of work I'd be doing. He wouldn't say — it was secret." He eventually ended up at the Clinton Engineer Works. Those who turned down jobs might end up being drafted into a special engineering detachment of the U.S. Army and sent to Tennessee, according to Smith.
Those atomic workers arrived at a place shrouded in secrecy. Locals knew that something mysterious was going on at the site, but only those who were part of the mission were allowed inside, past the guarded gates on the access roads. The atomic facilities themselves were surrounded by additional security. The work itself was highly compartmentalized, so that most people knew only about the small portion of the effort that they themselves were working on, and only a select few knew that the overarching mission was to help make the atomic bomb. "People who were going to a particular building could only go to that building," Smith explains.
A Self-contained Community
To keep information from getting out, Oak Ridge became a self-contained community with most everything that its workers needed. As Falstein described in his 1945 article, the secret city had stores, movie houses, a high school, a bank, a 300-bed hospital, tennis and handball courts, and even its own symphony orchestra, led by a Manhattan Project scientist. People who lived there tended victory gardens, raised families and led what was pretty much a normal American existence — that is, except for the secrecy that surrounded them and their work. A billboard reminded workers, "Let's Keep Our Trap Shut." They knew that they had to be cautious not to say anything about their jobs to anyone, even their own spouses, "We'd sit around the dinner table and the strain was terrible," a young scientist told Falstein in 1945.
Though there's no evidence that German or Japanese spies ever managed to infiltrate the Clinton Engineer Works, a Soviet spy named George Koval did manage to get a job there, and apparently passed along information about the atomic work to the Soviets. In 2007, he was honored posthumously with a Hero of the Russian Federation medal, that nation's highest honor, by Russian President Vladimir Putin, as detailed in this 2009 Smithsonian article.
Meanwhile, the Clinton Engineer Works had to accomplish the difficult task of producing uranium-235.
There's only a tiny amount of the stuff — 0.7 percent — in uranium ore, most of which is uranium-238, which doesn't fission as easily. And a bomb such as Little Boy, the one dropped on Hiroshima, required 141 pounds (63.9 kilograms) of uranium-235, according to Tom Zoellner's book "Uranium: War, Energy and the Rock that Shaped the World."
"You've got to separate a lot of material to get the amount of 235 that you need," Smith explains.
To solve that problem, the Clinton Engineer Works' Y-12 plant used special devices called calutrons, which utilized the electromagnetic separation process developed by Nobel-winning physicist Ernest O. Laurence at the University of California, Berkeley. The calutrons used heat and powerful magnets to separate the two isotopes. Smith compares the process to holding a golf ball — representing the heavier isotope, uranium-238 — attached to a rubber band in one hand and a similarly attached ping-pong ball representing lighter uranium-235 in the other, and then tossing them both in the air." The heavy object makes a larger arc, because of centrifugal force," he explains. Once the two isotopes were separated, it was possible to collect the lighter uranium-235 isotope. Even so, to gather enough uranium-235, the Y-12 facility employed 22,000 workers to run 1,152 calutrons literally around the clock.
Meanwhile, another part of the works, the X-10 Graphite Reactor, used neutrons emitted from uranium-235 to convert uranium-238 into an isotope of a different element, plutonium-239, another easily fissionable material suitable for making atomic bombs. As Smith explains, after X-10 demonstrated that the process could work, the actual plutonium used to make Fat Man, the bomb dropped on Nagasaki, was produced in the B Reactor at the Hanford Engineer Works near Richland, Washington. (From Seattle Business Magazine, here's an article on that facility.)
Finally, on Aug. 6, 1945, the world got to see the results of the secret city's labors, when an atomic bomb containing uranium-235 produced there was dropped on the Japanese city of Hiroshima. The Knoxville, Tennessee News-Sentinel's front page headline proudly proclaimed: "ATOMIC SUPER-BOMB, MADE AT OAK RIDGE, STRIKES JAPAN." (That wasn't completely correct — though the uranium-235 came from Tennessee, parts of the bomb were made at three different plants, so that none of them would have the complete design, according to atomic historians Lillian Hoddeson, Paul W. Henriksen and Roger A. Meade in their book "Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945.")
After the war, the various parts of the once-secret Tennessee atomic complex were split up. Part eventually was reborn as the Oak Ridge National Laboratory, which helped pioneer the field of nuclear medicine, producing isotopes for use in treating cancer and as diagnostic tools, in addition to doing cutting-edge research in areas ranging from nanotechnology to wireless charging of electric vehicles. Another portion became the Y-12 National Security Complex, which produced components for tens of thousands of thermonuclear weapons in the U.S. arsenal during the Cold War, and later helped disassemble U.S. and former Soviet nuclear weapons. A third part is now the site of the East Tennessee Technology Park.