Recently, a draft of the US nuclear posture review leaked to HuffPo.
https://www.defensenews.com/space/2018/01/12/nuclear-posture-review-draft-leaks-new-weapons-coming-amid-strategic-shift/
It acknowledges the existence of a rumored Russian standoff weapon, "a new intercontinental, nuclear-armed undersea autonomous torpedo" capable of "a top speed in excess of 56 knots and can descend to depths of 3,280 feet below sea level." The payload is a 100MT nuclear warhead. Wow.
https://www.defensenews.com/space/20...osture-review/