It also was because we knew where their subs were from the time they left port until they returned.
Adelman's view aside, Star Wars worked exceptionally well in limited tests, and even somewhat in Jerry-rigged Patriot missiles in the Gulf. What Gorby knew was that we COULD do it and if we made it any kind of priority at all, we could do it in a matter of years. He knew in WW II we went from nothing to 95,000 tanks in 4 years, and made Liberty Ships in FOUR DAYS!
He knew if we got serios we could render their whole missile fleet junk.
But here is something Adelman's didn't mention: I did an article in 1988 showing that NO ONE properly accounted for Soviet missile/warhead failure rates! When those were taken into account, Soviet threat levels in missiles fell 20% at launch! at separation! and at impact. That's one hell of an attrition. Multiply that by a Star Wars only 80% effective? . . . They were screwed