RDS-1
The Soviet Union detonates its first nuclear weapon, internally code named RDS-1, near a specially-built “dummy” village which includes various structures, aircraft and other military hardware, and livestock, all present to test the effects of an atomic weapon detonation in their vicinity. Western intelligence is caught off guard when the radioactive fallout is picked up by detection equipment on weather reconnaissance flights between Japan and Alaska, as the Soviets were not expected to have their own nuclear weapons until sometime in the 1950s. This is a turning point in the Cold War, initiating the race toward the next evolution of nuclear weapons: the hydrogen, or thermonuclear, bomb.