that's an interesting idea
i have to say myself, i wish there were a few more units, but that's not how i would want those new units to be used personally (i'd prefer new units that actually fight
STILL, if you want to use subs like that, a way to debuff those attacks would be to make it so that the subs have to fight defending player's naval forces (including subs) to be able to launch the nuke. it would give some more usefulness to navy which isn't a bad thing