if subs were added, only the small type subs of japan,germany and italy should be added.....for a good reason.besides limiting amount of torps... you could up a small sub anywhere you could up a pt boat(from a base only-not a cv) and you could hunt a cv near a base. you would probably have more than one attack as the cv would probably go back an forth a few times out of the shore battery range/arc of fire(field of fire). and so the sub would work. it should however be visible when it is at torpedo depth under the water,and be able to be sunk by depth charges. depth charges would have to be added to cv's.pt's and plane ords for the job. submarines would have to surface to recharge batteries and get oxygen every so often...say every 1 hour, even if it has to surface for 1 minute....that would be enough time to kill it with normal guns...or something like that.