The RDS-1 (Russian: РДС-1), also known as First Lightning (Russian: Пе́рвая мо́лния, romanized: Pyérvaya mólniya, IPA: [ˈpʲervəjə ˈmolnʲɪjə]), was the first nuclear weapons test that was conducted by the Soviet Union. It was detonated on 29 August 1949 at 7:00 a.m. Kazakhstan Time (decree time) (UTC+06:00), at the Semipalatinsk Test Site in the Kazakh Soviet Socialist Republic, and yielded 22 kilotons of TNT. It was roughly based on the American design, Fat Man, and the United States assigned it the code-name Joe-1, in reference to Joseph Stalin.