Manhattanproject

The Manhattan Project was a research and development program during World War II that produced the first nuclear weapons. Initiated in 1942 by the United States with support from the United Kingdom and Canada, it arose from concerns that Nazi Germany might develop an atomic bomb. The project brought together thousands of scientists, engineers, and military personnel under strict secrecy, with the aim of creating a deployable weapon as quickly as possible.

The program was organized under the U.S. Army Corps of Engineers as the Manhattan Engineer District and encompassed several major sites. Los Alamos National Laboratory in New Mexico served as the primary design and assembly center for the weapons. Oak Ridge in Tennessee produced fissile material through electromagnetic separation (Y-12), gaseous diffusion (K-25), and thermal diffusion (S-50). The Hanford Site in Washington housed large-scale plutonium production reactors. Early milestones included the first controlled nuclear chain reaction, achieved at Chicago Pile-1 in 1942, and the Trinity test in July 1945, which demonstrated an implosion-type plutonium device.

The project culminated in two weapons being used in warfare: Little Boy, a uranium-235 gun-type device dropped on Hiroshima on August 6, 1945, and Fat Man, a plutonium implosion device dropped on Nagasaki on August 9, 1945. The rapid end of World War II in the Pacific and the subsequent political and military realignments led to enduring effects on international security, arms control, and scientific research. In total, the project employed roughly 120,000 to 130,000 people and cost about $2 billion at the time. Its legacy includes the postwar development of civilian and military nuclear programs and institutions such as the Atomic Energy Commission, later reorganized into the Department of Energy.