Beginning in late 1942, thousands of construction workers, engineers, scientists, technicians, and others converged on quiet East Tennessee farmland at Oak Ridge to carry out the Manhattan Project’s highly secret top-priority work. Most workers did not know the full purpose of their labor, but in just two-and-a-half years their science and engineering made possible the atomic bomb before Hitler’s Germany could do so. In August 1945, many residents of the Secret City learned for the first time that their work had helped create a weapon seen as instrumental in ending the brutal six-year war in which 54 million people died and in avoiding an invasion of Japan that would have cost many lives. Oak Ridge’s role in the vast national effort was valued at $1.1 billion, and the city’s gates were opened to the outside world on March 19, 1949, as it began transitioning toward peacetime nuclear work and a more normal community.