The RDS-1 (), also known as Izdeliye 501 (device 501) and First Lightning (), was the nuclear bomb 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 detonated on 29 August 1949 at 7:00 a.m., at the Semipalatinsk Test Site, Kazakh SSR, after top-secret research and development as part of the Soviet atomic bomb project. Description The weapon was designed at the Kurchatov Institute, then at the time officially known as "Laboratory № 2" but designated as the "office" or "base" in internal documents, starting in April 1946. Plutonium for the bomb was produced at the industrial complex Chelyabinsk-40. The RDS-1 explosive yield was 22 kilotons TNT equivalent, similar to the US Gadget and Fat Man bombs. At Lavrentiy Beria's insistence, the RDS-1 bomb was designed as an implosion type weapon, similar to the Fat Man bomb dropped on Nagasaki, Japan; RDS-1 also had a solid plutonium core. The bomb designers had developed a more sophisticated design (tested later as RDS-2) but rejected it because of the known reliability of the Fat Man type design, the Soviets having received extensive intelligence on the design of the Fat Man bomb during World War II, which was discovered in the espionage case of Julius and Ethel Rosenberg and during the Venona project. To test the effects of the new weapon, workers constructed houses made of wood and bricks, along with a bridge, and a simulated metro railway in the vicinity of the test site. Armoured hardware and approximately 50 aircraft were also brought to the testing grounds as well as over 1,500 animals to test the bomb's effects on life. In a sector of artillery about 100 guns and mortars were placed at distances ranging from 250 to 1,800 meters from ground zero. At distances 500 to 550 meters from ground zero artillery pieces were either totally destroyed or needed factory repair. The resulting data showed the RDS explosion to be 50% more destructive than originally estimated by its engineers. There are several explanations for the Soviet code-name of RDS-1, usually an arbitrary designation: a backronym "Special Jet Engine" (, Reaktivnyi Dvigatel Spetsialnyi), or "Stalin's Jet Engine" (, Reaktivnyi Dvigatel Stalina), or "Russia does it herself" (, Rossiya Delayet Sama). Later weapons were also designated RDS but with different model numbers. Mikhail Pervukhin served as the chairman