Able Archer 83 is the codename for a command post exercise carried out in November 1983 by the North Atlantic Treaty Organization (NATO). As with Able Archer exercises from previous years, the purpose of the exercise was to simulate a period of conflict escalation, culminating in the US military attaining a simulated DEFCON 1 coordinated nuclear attack. Coordinated from the Supreme Headquarters Allied Powers Europe (SHAPE) headquarters in Casteau, Belgium, it involved NATO forces throughout Western Europe, beginning on November 7, 1983, and lasting for five days.