One might say that subs are the only truly strategic component of nuclear arms.
I used to think this. But land-based missiles are essential for MAD, as a nuclear sponge and by being cheap. They also protect against a technological horizon over which subs are unmasked. (There is a great scene in The Expanse which contemplates such a horizon.)
What I can’t get my head around are nuclear bombers, which largely seem to be for posturing [1].
[1] https://www.airuniversity.af.edu/Portals/10/SSQ/documents/Vo...
Posturing is super important, strategically, though. Also, nuclear-capable bombers double as conventional bombers, so there’s that.
I’ve read speculation that Russia boomers are followed at all times by at least one fast attack, and they can listen for sounds like missile bay doors opening. I have no sources, but given the state of Russia navy it seems plausible.