New York, New York

Columbia University pictured in 1952, five years after the end of the Manhattan Project. Pupin Hall is located at extreme left.

Anthony Angel/Library of Congress

Prior to moving to Oak Ridge in the summer of 1943, the Manhattan Project was headquartered at 270 Broadway in lower Manhattan, New York as part of the North Atlantic Division of the US Army Corps of Engineers. With an initial name of “Laboratory for the Development of Substitute Materials”, project leader General Leslie Groves, fearing the name would cause unwanted attention, changed it to “Manhattan Engineer District.” This name would soon be shortened to the “Manhattan Project.”

In addition to Manhattan initially housing the project’s headquarters, the city was also home to Columbia University, where scientists including Enrico Fermi, Leo Szilard, I.I. Rabi, and others worked in the code-named Substitute Alloys Materials Laboratory. In 1939, in the basement of Pupin Hall, scientists first observed nuclear fission on US soil. In the basement of Schermerhorn Hall, Fermi and colleagues constructed a subcritical uranium and graphite nuclear reactor, the precursor to the Chicago Pile, the world’s first nuclear reactor which reached criticality on the University of Chicago campus in December 1942.

By 1943, chemist Harold Urey oversaw more than 700 workers experimenting with uranium enrichment processes, including the gaseous diffusion method which would be introduced on an industrial scale at the K-25 plant in Oak Ridge. Throughout Manhattan, more than 5,000 people contributed to the success of the Manhattan Project.