The Soviet Union conducted its first nuclear weapons test, detonating the 22-kiloton RDS-1.

The nuclear weapons tests of the Soviet Union were performed between 1949 and 1990 as part of the nuclear arms race. The Soviet Union conducted 715 nuclear tests using 969 total devices by official count, including 219 atmospheric, underwater, and space tests and 124 peaceful use tests. Most of the tests took place at the Southern Test Site in Semipalatinsk, Kazakhstan and the Northern Test Site at Novaya Zemlya. Other tests took place at various locations within the Soviet Union, including now-independent Kazakhstan, Uzbekistan, Ukraine and Turkmenistan.

TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. A ton of TNT equivalent is a unit of energy defined by convention to be 4.184 gigajoules. It is the approximate energy released in the detonation of a metric ton of trinitrotoluene (TNT). In other words, for each gram of TNT exploded, 4.184 kilojoules of energy are released. This convention intends to compare the destructiveness of an event with that of conventional explosive materials, of which TNT is a typical example, although other conventional explosives such as dynamite contain more energy. A related concept is the physical quantity TNT-equivalent mass, expressed in the ordinary units of mass and its multiples: kilogram (kg), megagram (Mg) or tonne (t), etc.

The RDS-1, also known as Izdeliye 501 and First Lightning, was the first test of a Soviet nuclear bomb. 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.