Use your flack guns for all small vessels (small costal, tugs, fishing boats and elcos
). Save your deckgun rounds for costal and small merchants.
Star shells can also be used against ships if the range is lower than 1500m.
Don't use torps to finnish off criple thats doing only one or two knots, use the deck gun, aiming at the waterline. This is a good tactic early in the war, but by 1942 most ships will be armed so torps will be the best option.
Small tankers, Costal and small merchants - 1 torp.
C2, C3, T2, T3, Victory ships - 1-2 torps
Troop ships and passenger liners - 2-3 torps
Sometimes you can use one torp on a ship and it will sink, using the vunability mod for the recogniction guide will help you place torp for maxium damage (troop ship - mag shot inline with aft mast will sink it 80% of the time, C2 & C3 - torp just in front of the bridge, T2 & T3 - torp just forward of the aft deckhouse/bridge, passinger liner - torp under the second funnel)
Sometimes it will take more (small merchant - 3 torps, C2 - 6 *&$@$! torps!) but that the way it goes.
Min fireing range is 300m if you don't want your torp to bounce of the side of the target. Learn to doge destroyers, the maybe dumb in the early years, but they'll get nasty as time goes on, plus you get more renown for sinking merchants than destroyers.
Sometimes you'll want to take them out (found a convoy with only one escort, one torp took care of him, and I got to go duck hunting with no bag limit!) or you'll need to take them out (get him before he gets you). 600 meters is the best range, as ther is little time for them to doge it. Use an electric if he dosen't know your there, or a steam set on high if he does. Set torps at 3 meters and aim for amidship.
Before firing torps it's best to open torpedoe tubes, it means less lag in time between the order to fire and the actual shot. This could mean the difference between a hit or a miss.
Good luck and good hunting, and remember, a torpedo brought home is a missed oppertunity!
