Unknown to Kennedy and his ExComm, the Russians had battlefield nuclear weapons in Cuba and came close to giving permission for their use against an American invasion, without further approval from Moscow [Chang & Kornbluh 1998; Blair 1993, page 109; Fursenko & Naftali 1997, pages 212, 242-243, 276]. Not knowing of these weapons, there was strong pressure within the ExComm and from Congress [Fursenko & Naftali 1997, pages 243-245] to invade Cuba and
remove Castro once and for all. Another ominous aspect of the crisis was uncovered when key players from both sides met on its 40th anniversary. A Soviet submarine near the quarantine line had been subjected to signaling depth charges, commanding it to surface, which it eventually did. Not until 40 years later did Americans learn that this submarine carried a nuclear torpedo and that the Soviet submarine captain, believing he was under attack, had given orders to arm it. Fortunately, the submarine brigade commander was on board, over-ruled the captain, and defused the threat of a nuclear attack on the American fleet [Blanton 2002].
...today, we are in the process of deploying a missile defense in Russia’s backyard (Poland and the Czech Republic) over strenuous Russian objections. A possible Russian response would be to threaten deployment of a similar missile defense in Cuba, much as our Jupiter missile deployment in Turkey was the stimulus for Khrushchev deploying his Cuban missiles [Burlatsky 1991, page 171].7 While these Cuban missiles would be defensive in nature, many Americans
would see them as intolerable. Among other concerns, there would likely be fears that these were offensive weapons disguised as defensive ones. (The Russians have voiced a similar concern over our deployment.)
gwern comments on [LINK] Brief Discussion of Asteroid & Nuclear Risk from paper by Hellman