The RDS-1 (Russian: РДС-1), also known as Izdeliye 501 (device 501) and First Lightning (Первая молния, 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 R&D project.