I was stationed at Ramstein W.Ge. during the exercise Able Archer and was ECM inspector and was rather intimately involved with what was happening.
The Soviet Union issued Germany an ultimatum about their desire for an oil pipeline through Germany and their intense dislike of seeing Germany reunited. This was mainly through the military GRU units instead of KGB probably since for the most part, the KGB was mostly a police unit and intelligence units not geared for world domination.
Our base went to full alert status, not a part of Able Archer when the Soviets amassed an invasion force from Czechoslovakia and we had a border conflict with them. Our sources of info was that the Soviet Union was going to invade the U.S. and we simply were acting to protect ourselves. That the Soviets claim they thought we were going to invade them is pure rubbish. We had no plans of first striking them. This was and is typical Soviet misinformation.
They in fact invaded us and we implemented our Stealth capabilities and were able to convince them not to come any further (a border conflict I suppose you could say). We were not so sure it would not end in a nuclear confrontation. Even though our superiors assured us we can take the Soviets on without resorting to nuclear weapons.
The truth of the matter is, the Soviets were planning on first striking the U.S. as far as our intelligence networking could ascertain and we simply were protecting against that possibility. The operation Able Archer as far as I know had absolutely nothing to do with any invasion plan formed by the U.S. military.