High Quality Content by WIKIPEDIA articles! Able Archer 83 was a ten-day NATO command post exercise starting on November 2, 1983 that spanned Western Europe, centred on the Supreme Headquarters Allied Powers Europe (SHAPE) Headquarters situated at Casteau, north of the Belgian city of Mons. Able Archer exercises simulated a period of conflict escalation, culminating in a coordinated nuclear release. The 1983 exercise incorporated a new, unique format of coded communication, radio silences, participation by heads of government, and a simulated DEFCON 1 nuclear alert.