Unsuspecting surfaced AI submarines would be the most logical to implement.
After that allowing sound tracking torpedoes to fell the foe beneath the surface for some initial period (shallow depth) while the AI transitions from surface to depth might also be reasonable.
Beyond that, an at depth duel would be most cumbersome and a higly improbable given the weaponary and sensor limitations of the time.
One case were guns were used to advantage was at Pearl Harbor were one of the mini subs attempting to enter Pearl was attacked and successfully sank by a DD Ward with a single round through the mini's conning tower. (the sub was recently discovered along with the hole)
A surface duel between pig boats would be realistic but I suspect the urge to dive would be overwhelming to any Captain and that course of action would inevitably lead to sensor limitation and loss of contact....
All in all the above logic and game limitations would be doable without major impacts and difficult code implementations. One might initiate these chance sub encounters based on operational areas, randomness, time during war, and perhaps a time of day with dawn and dusks and lighter evenings preferred...
