Able Archer 83 was the annual NATO Able Archer exercise conducted in November 1983. The purpose for the command post exercise, like previous years, was to simulate a period of conflict escalation, culminating in the US military attaining a simulated DEFCON 1 coordinated nuclear attack. The five-day exercise, which involved NATO commands throughout Western Europe, was coordinated from the Supreme Headquarters Allied Powers Europe (SHAPE) headquarters in Casteau, Belgium.

The 1983 exercise, which began on November 7, 1983, introduced several new elements not seen in previous years, including a new, unique format of coded communication, radio silences, and the participation of heads of government. This increase in realism, combined with tense relations between the United States and the Soviet Union and the anticipated arrival of Pershing II nuclear missiles in Europe, led some members of the Soviet Politburo and military to believe that Able Archer 83 was a ruse of war, obscuring preparations for a genuine nuclear first strike. In response, the Soviet Union readied their nuclear forces and placed air units in East Germany and Poland on alert. The Soviet 4th Air Army began loading nuclear warheads onto combat planes in preparation for war. The apparent threat of nuclear war ended when U. S. Lieutenant General Leonard H. Perroots advised against responding to the Warsaw Pact military activity, which ended with the conclusion of the exercise on November 11.

The exercise attracted public attention in 2015 when the President's Intelligence Advisory Board 1990 report on the exercise was declassified. Some scholars have argued that Able Archer 83 was one of the times when the world has come closest to nuclear war since the Cuban Missile Crisis in 1962. The declassification of related documents in 2021 supported this notion. Other scholars have disputed that Able Archer 83 almost led to nuclear war.