This dissertation seeks to explore how the Manhattan Project came to be seen as a triumph of physics and physicists. Vast in size and international in scope, the effort to develop the atomic bomb required the contributions of scientists, engineers, industrialists, and military officers to achieve success. Yet the postwar stories and histories of the Manhattan Project largely focused on the contributions of physicists, primarily at Los Alamos, an attribution which in turn helped propel the American physics community to new heights of prestige, funding, and numbers in the years following World War II. That attribution has its roots in a specific document: the Smyth Report, the official governmental report on the development of the atomic bomb, issued shortly after the bombing of Nagasaki, to explain to the American public the nature of the weapon that had been deployed in its name. Written by a Princeton University physicist, Henry DeWolf Smyth, and formally titled Atomic Energy for Military Purposes, the Report emphasized the contributions of physics. It did so for two reasons: Smyth's own sense of what constituted interesting science, as well as the security determination that the release of basic physics information was less likely to reveal critical secrets than the release of chemical or engineering information. These two considerations, Smyth's interests and security concerns, yielded a report that focused on physics and physicists, while limiting discussion of others' contributions. The impact of the Smyth Report was vast. As the sole source of technical information about the atomic bomb available to a clamoring nation, the Smyth Report was widely read and cited. For the military, the already-cleared Smyth Report provided a convenient template for determining what information about the bomb could earn security clearance. ensuring that Smyth's decisions about what to include or omit would shape the permissible public discussion for years to come. Even as the Smyth Report itself largely fell out of public view during the Cold War, both the historiography and popular writing about the Manhattan Project significantly followed its contours, continuing to portray the work of the Manhattan Project as primarily the work of physicists.