I think the sub are better modeled in Anniversary than in any preceding A&A. To still improve the modeling we should have that sub could be hit only by DD, and DD allows CA and aircrafts to hit subs. BB and AC have no depth charges or torpedoes for attacking the sub. Thay may only maneuver for avoding subs torpedoes or trying to ram a surfaced sub.
Submerged sub may not be hit by the guns of the surface ship. So the better defense for sub is to submerge. No any sub in a real battle stay on the surface for being attacked by ship guns or aircraft bombs.
In the real fleets it does not esist the “escort submarine”. It exist the escort DD, or the escort AC etc.
Submarine operate separated from the rest of the fleet, in autonomous operation.
They were not around during fleet engagement they were too much slow for staying togheter with a battle fleet. They cannot maneuver nor stay in formation with ships that have, at least, the double of their speed.
They were specialized attack vessel, which task has been lurking around to hit passing ships.
DD and aircrafts had the task of dealing with subs.
When Bismark was sunk in battle with the Home Fleet there were a lot of Uboote around the battle area, they arrived just in time to disturb the UK DD rescuing of the Bismark survivors, after the battle.
In the battle of Midway there were a lot of Japanese subs around the islands with the task of intercepting and attacking the USA ships. Before the battle the saw and attacked nothing.
Yorktown, heavily damaged, and on the way for the Hawaii was sunk, after the battle, by one of the japanese submarine still patroling the sea.