The project involved scientists from the USA and Great Britain, including many Jewish scientists who had fled Nazi-occupied Europe. The task went beyond science, requiring a massive effort on a huge industrial scale. Factories and laboratories across America were involved, the most notable sites being at Oak Ridge, Tennessee; Hanford, Washington; Los Alamos, New Mexico, and the Lawrence Radiation Laboratory in Berkeley, California.
The British had achieved substantial progress and passed on their findings to their American allies under the codename Tube Alloy.
The project was headed by Lieutenant General Leslie R. Groves Jr. of the US Army Corps of Engineers. Groves had a reputation for getting the job done and saw the Manhattan Project through to its conclusion and the bombing of Hiroshima and Nagasaki in August 1945.