Submarine launched ICBMs probably wouldn't be valuable without nuclear weapons though: they're valuable because they're a guaranteed second-strike capability to a nuclear first strike - you might plausibly get the land and air launchers, but there's no way to be sure you got all the subs and you only have to miss 1 (i.e. no country would survive losing 28 major cities).

Without nuclear weapons, they're kind of pointless - you don't inflict enough damage to warrant the expense. But the first strike is also so much more survivable.