Joe One (or Joe-1; USSR version RDS-1 (Reaktivnyi Dvigatel Stalina; Stalin's Rocket Engine)) was the western name for the first Soviet atomic bomb test, on August 29, 1949 at Semipalatinsk, Kazakhstan. The yield was 22 kilotons. At Beria's insistence, the device was a more or less copy of the United States Gadget/Fat Man design.
The Soviets called it First Lightning. See Soviet atomic bomb project.
Its power was roughly equivalent to about 20 kilotons of TNT, similar to the American weapon dropped on Nagasaki, Japan. Its development was years ahead of American military-intelligence projections and came as a nasty shock to the West.
The American codename was in reference to Joseph Stalin, the Soviet dictator.
