Thanks for welcome! Nice forum indeed! :-)
So from what Iīve learnt so far, naval gunnery in stock SH3 works like this (please correct me if Iīm wrong):
- Ships donīt sink because of flooding primarily, but because I score a certain amount of hitpoints that is higher than the shiptype in question can withstand. If I hit the bow, well above the waterline, hitting
no critical parts, the ship will sink regardless if only I hit it with enough shells.

- There are weak points that I can hit repeatedly for inflicting more damage, sinking the ships faster.
If I combine these two I figure it is best to hit the hull right under, or slightly forward of the funnel, repeatedly, until the ship is destroyed. You know - Iīm slightly disapointed, but hey, itīs still a great game!
As to the HE vs AP sidenote: I figure the deck gun in SH3 is much simpler to aim than in real life. Perhaps the subs didnīt bring AP since it wasnīt probable that the gun crew would be able to hit consistently below the waterline anyway. Since the AP round would be much less damaging than HE rounds,
unless it actually makes holes under the waterline, it may seam rational to bring only rounds that will do the greatest amount of damage to the biggest target (the parts of the ship that is above the waterline) But what do I know...