I think we could probably devote a whole board to the sub rules. I think in Classic (bot many games of Classic under the belt went to that backwards via Europe) subs could come into a zone, shoot, and leave without being shot at. Not sure on that though.
Our problem was we were not conducting opening fire every round that subs were still on the battle board. We would have opening shots then treat them just like any other naval units.
The sub rules are different in all four versions of the game with subs that much I’m very clear on. The sub rules for Revised I’m very clear on because I think they are the cleanest.