The OP was suggesting that a submarine-based nuclear deterrent still has relevance. I don't believe it does. As noted by Flying Serpent, there are more innovative means of delivering nuclear weapons to the doorstep of your enemy.
You must learn to think outside the box as your adversaries, both current and potential, are wont to to. Chuckling to yourselves over how the Americans never learned their lesson from their visit to this country (Viet Nam) is of little use when you go making the very same mistakes in Iraq and Afghanistan.
If people have a belief in a political system, a religion or a culture and they're prepared to retain that belief to the point of death, all you can do is kill them or struggle to subjugate them. So if they're not interfering in your world, let them be.
The most effective argument against a political system, a religion or a culture is a better, kinder, more compassionate or successful version of the aforementioned. Spend your billions developing that, and you may find you offer a better argument for following your philosophy than the possibility of a personal meeting with something from a stinky* submarine.
* Why do RN boats always smell so bad?