Able Archer 83 was a military exercise conducted by NATO that took place in November 1983. It simulated a period of heightened nuclear tensions between NATO and the Warsaw Pact, leading to concerns that it could have been mistaken for a real attack by the Soviet Union. The exercise is considered by some to be one of the closest moments the world came to nuclear war during the Cold War. It was the annual Able Archer exercise conducted in November 1983. The purpose of the 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.

A military exercise, training exercise, maneuver (manoeuvre), or war game is the employment of military resources in training for military operations. Military exercises are conducted to explore the effects of warfare or test tactics and strategies without actual combat. They also ensure the combat readiness of garrisoned or deployable forces prior to deployment from a home base.