WW2 era "submarines" are not truly submarines, but submersible ships. The implication is that subs of that era travel so much better on water surface than when submerged, so they actually spent most of the time on surface, and only submerge when stealth / evasion is required. Hence, it was feasible to have deck gun on subs as its effectiveness in harassing unarmed merchant ships outweighed the hydrodynamic penalty it carries.

In sharp contrast to WW2 subs, modern subs' hydrodynamic hull design makes them so much more suitable to travel submerged. Also, gone are the days of visual target acquisition when anything can be detected by hugely improved surface radar and underwater sonar detection technologies. Not to mention improved torpedo target tracking. Hence, surface gun battle for subs is no longer feasible. Subs have become the stealthy assassin from the depths. Something must go terribly wrong for a modern sub to get entangled in close range surface gun fight.

Anyway, mind story a bit how you actually sunk a battleship with 30+ shells without getting sunk? I would get rekt almost immediately by mere destroyer guns if I stayed on surface longer than a minute lol. Not sure if SH1 was much easier to play than SH3.