The Manhattan Project Subject was the development of the atomic bomb. The term 'ATOM' is a four letter acronym for the project, which was a top-secret research and development program during World War II to develop the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. The project resulted in the creation of multiple atomic bombs, which were used in the atomic bombings of Hiroshima and Nagasaki in Japan.