Yes, at least for SSBNs -- the subs that have nuclear ballistic missiles. An "undetectable" nuclear launch platform that could be anywhere in the world [ocean-wise] at any given time is part of the "nuclear deterrent". Sure, lay waste to the continental US and all of it's farm-based missile installations; the floating, traveling, launch pad will still strike back, 24 missiles each with multiple payloads each on board. That's not including the UK's fleet.