Tailing some portion of missile subs won't do - a single missile sub is an existential threat so deterrence isn't destabilized until the adversary can credibly

Tailing some portion of missile subs won't do - a single missile sub is an existential threat so deterrence isn't destabilized until the adversary can credibly eliminate all of them within ~10 minutes. It takes a nuclear sub to trail a nuclear sub. NK and China have exclusively, and primarily (respectively) diesel subs. These have to surface and run their engines to charge batteries. They cannot make 20+ knots submerged for long, and they cannot track deeply submerged submarines from the surface. Surfacing and running diesels would make their presence known. They cannot range far from port, and certainly cannot track missile boats under the arctic ice. Russia has a sufficiently large nuclear fleet, but it is outdated and probably outclassed by US technology. There is probably greater disparity between the powers than existed during the cold war, at which time deterrence was credible.