United States. Army. Corps of Engineers. Manhattan District

The Manhattan District was not an individual author but a U.S. Army Corps of Engineers command created in 1942 to manage the Army side of the atomic bomb program. Its name came from standard Corps practice of naming districts after their home city, since early work was centered in Manhattan, and the label also helped conceal the project’s real purpose.

Under Brigadier General Leslie R. Groves, the district oversaw an enormous network of research, construction, security, and production sites, including Oak Ridge, Hanford, and Los Alamos. What began as an engineering district grew into the operational backbone of the Manhattan Project, bringing together military officers, scientists, industrial contractors, and a workforce that reached into the hundreds of thousands.

The name also lives on through the "Manhattan District History," a large multi-volume record commissioned near the end of World War II to document what the organization had done and how it worked. That history remains one of the key primary-source records for understanding the scale, secrecy, and lasting impact of the project.