Wasn’t that in reaction to one of our training exercises?
Able Archer WAS that name of a US training exercise that had been ramped-up to make it more realistic. We’d also done psyops to antagonize the Russians for a year or more in advance and they didn’t know what we were doing so they increased their military readiness level. That was in the Cold War era, now a similar situation would be extremely unlikely as things presently stand.