[El Gato]

That will only be a first step – the best nuclear deterrence submarines are nuclear-powered, which means they will not only be quiet, but they will never have to surface or snorkel to recharge their batteries

Unless they use Air Independent Propulsion. Then they will be at least as quite as a nuke, and will have plenty of submerged endurance for the SSB mission. They also don't need nearly the range for their missiles, since their principal target would be Pakistan, a country no part of which is far from the sea, and China, which is also for the most part not far from the sea.

[Bulwark]

Unless they use Air Independent Propulsion. Then they will be at least as quite as a nuke, and will have plenty of submerged endurance for the SSB mission

Dumb question, but what is Air Independent Propulsion?

I know that diesel electric subs are actually quieter than nukes, at least when they're running on batteries. The ex-UK upholder class (I think) which are now canadian subs were designed to hunt Russian nuclear subs. The only drawback was their range and the need to refuel.