Kind of expensive fun...
What version do you play ? The rudder section is risky because of all the round parts where the torp can bounce if hitting at a too great angle.
It is generally more effective with the deck gun to hit under the waterline rather than on the decks... but obviously you're not too worried about being effective...
I like to make it short, aim for engine room/fuel bunker and 1 or 2 torps do the job... I keep deck gun shells for the small things like tramps and flak guns for the PT boats.
I don't mess around with airplanes, my weapon of choice is ahead flank dive planes all the way down, rudder 20 to the right or left...