The RDS-1 , also known as Izdeliye 501 (device 501) and First Lightning (, Pervaya molniya), was used in the Soviet Union's first nuclear weapon test. The United States assigned it the code-name Joe-1, in reference to Joseph Stalin. It was exploded on 29 August 1949 at 7:00 AM, at Semipalatinsk, Kazakh SSR, after a top-secret research and development project.