The highly-classified project to manufacture an atomic bomb began in June 1942. Led by the U.S. Army's Manhattan Engineer District, it later came to be called the Manhattan Project.
The enrichment of uranium and production of plutonium required an enormous plants and cooperation from the private sector. The development of the atomic bomb was an immense military engineering enterprise that mobilized military, scientific, and industrial personnel nationwide. Completion of the atomic bomb took three years and $2 billion.