[Boris The Spider]

I'm thinking of a "hit box" around the periscope. True, it would be very difficult but having the potential to sink a submerged sub would be extraordinary. I know "hit boxes" are modeled in the game. Surface ships have them. A torpedo/bomb hit amidships does more damage that just aft or forward of it. Hits to the bow and stern have no affect.
If a "hitbox" is possible they should be added to the bow and stern of all surface ships. A bow hit by a torpedo or bomb would slow the ship and cause a minor list much like what happened to the Yamamoto (shown here)



A stern hit would make the ship turn in circles much like what happened to the Bismark's steering gear.
Torpedo's could remain ineffective against submerged subs.

Just a thought.