The civil servant was given only one clue where she would be going: a train ticket to Knoxville, Tennessee. She packed her best clothes, wore a new pair of shoes, and gave herself entirely to the project at hand: don’t ask questions, don’t talk unnecessarily, do your part to win the war. She arrived at a place that was more of a camp than a town, half-built prefabricated houses, an administration center, three reactors, and a foot of mud sure to suck off any shoe that stepped in it. On the books, she had arrived at the Clinton Engineer Works, a refinery plant for “Tubealloy.” Off the books, she had arrived at Site X of the Manhattan Project, where uranium would be enriched before it was shipped to Site Y in Los Alamos for use in “The Gadget.”

In The Girls of Atomic City: The Untold Story of the Women Who Helped Win World War II (public library), Denise Kiernan tells the story of the Oak Ridge center of the Manhattan Project, a town of 70,000 workers — primarily women — who lived in a camp-like environment of propaganda, barbed wire, checkpoints, code words, and spies, while working a thousand different jobs, all of which contributed to the events of August 6, 1945 and the dropping of the atomic bomb.

Women who had graduated from high school but couldn’t afford college could take the civil service exam. In a matter of months, they might be transferred to jobs in Washington, D.C., New York, or even abroad, without being informed where they were going or how long they would be there. Workers transferred to Oak Ridge were told to get on a train to Knoxville. College-educated women were recruited for their skills, but not always for their specialties. One woman who had wanted to be an engineer accepted a job as a statistician, which was considered more appropriate for her gender. Unskilled local women were also necessary to the project, and these locals often found themselves applying for work at the very place which had evicted their families.

Once at Oak Ridge, the workers were fingerprinted, interviewed, assigned a job, and given a clearance badge. Housing was limited and cramped in dormitories that often didn’t have heat. Food at the cafeteria was in short supply and lines were long. Everywhere there was mud, ruining shoes and clothes, and dirtying hallways. One employee remarked that the entire operation seemed more like camping than living, but work had opened up for women and it was their patriotic duty to take it.

Officially members of the Clinton Engineer Works, the employees at Oak Ridge adhered to a coded language whose real meanings were known to few. The Clinton Engineer Works was a waystation for “Tubealloy,” or uranium. Those higher up knew that the Tubealloy was being enriched at the Oak Ridge power plants for “the Gadget.” In official documents, Oak Ridge was known as “Site X,” and Los Alamos as “Site Y.” Billboards greeted workers throughout the day: “Your pen and your tongue can be enemy weapons. Watch what you write and say…” The local newspaper, the Oak Ridge Journal, wasn’t allowed to print the names of anyone in its columns. Some women were specially recruited to spy on each other, reporting any breaches in security to the higher-ups.

Tennessee was a Jim Crow state, and while the project wasn’t officially segregated, it abided by segregation in practice. All African-Americans on the project were laborers, domestics, or janitors. Married men and women were forced to live apart in huts with up to five people, while white workers were housed in dormitories and single family dwellings. Women were only allowed to visit their husbands if they had the proper clearance and documentation, proving they were married.

On August 6, 1945, the atomic bomb dropped on Hiroshima killed in an instant the equivalent population of the project at Oak Ridge—more than 70,000 people. In the President’s address to the nation about the dropping of the atomic bomb on Hiroshima, he mentioned the work done at sites near Santa Fe, New Mexico and Oak Ridge, Tennessee. This was the first that anyone had heard about their involvement with the atomic bomb. Secretary of War Henry L Stimson, explained that the workers had been rigorously kept in the dark:

The work has been completely compartmentalized so that while many thousands of people have been associated with the program in one way or another, no one has been given more information concerning it than was particularly necessary to do the job.

This, however, was giving the employees at Oak Ridge little credit. One chemist, who analyzed product from one of the reactors, knew that she was doing was atomic in nature — but she didn’t have enough pieces to puzzle together the larger picture. Her superiors knew more, but they never talked about it. No one talked in this town of 70,000. For three years. they had kept their work a secret from the outside world, and most impressively, from each other.

A lively story about the tens of thousands of women who made the bomb — from the power-plant janitor struggling each day through the mud to the exiled physicist in Sweden — The Girls of Atomic City offers a bottom-up history revealing that the atomic bomb was not simply the product of J. Robert Oppenheimer’s genius, but also of the work of women at every level of education and class.

Photographs by Ed Westcott courtesy American Museum of Science and Energy, Oak Ridge

Michelle Legro is an associate editor at Lapham’s Quarterly. You can find her on Twitter.