If it's an SSN, it has all of a dozen VLS tubes for all missions. A B-52 can carry twenty any given sortie. How hard would it be to simply have a couple B-52s on airborne alert like the bad old days if a crisis warranted it? That would be the equivalent of 3+ SSNs on station even if we assume they all carry nothing but nukes in their VLS. Unless the intent is to fill up the SSGNs with nukes to actually have some kind of persistent, tangible capability, I don't see the point of having an entire new missile program for the minimal redundancy a few nukes on an SSN will provide. And I personally think the SSGNs VLS tubes need to be retained for conventional weapons.A sub can sit out there for weeks at a time undetected. Also, if you're using the B-52, you have to USE the B-52. Maybe you want it for other things.I'd argue that if your air launched missile has a 2000km range, no one is going to see it coming anyway. What is the functional difference between a B-52 or a sub launching a cruise missile a couple hundred miles off the coast of a country like Russia or China?Because people can see a bomber coming but not a sub. Therefore less reaction time. I think sub-sonic cruise missiles are a relatively poor delivery mechanism in the modern age anyway. Hypersonic weapons are the way forward.But the sub launched missile isn't any more stealthy than the air launched missile, so again I'm not seeing the benefit. Why not just buy more air launched missiles instead?