Alex with respect to the ship sinkings: VonHelsing did a fantastic job in the damage model in GWX and in my opinion it's really close to reality. The GWX Damage Model sinks ships in three ways. By structural damage (you can call it "Hit Points"), by flooding internal compartments and by hitting critical areas. Now each torpedo that is fired in GWX has a random effect in the ship and that effect depends on a number of parameters (where it hits, the angle of impact etc). Generally speaking small ships (Tramp Stramers, Small Merchants etc) will go down with one torpedo (well most times at least) within a couple of hours maximum. Larger Ships will probably require a second, but there are not many merchant ships that will need a third one. My suggestion to manage to sink ships quickly and with one torpedo is to try to hit them in their critical compartments. These are either the ammo bunkers, the fuel tanks or the engine rooms. Every time you hit a ship make a mental note of where the torpedo hit and what the result was. That way you will soon manage to recognise (and remember) the weak spots in each ship type. If you need more info check out the chart I gave you. It is for stock SH3 and doesn't work (fully at least) in GWX, but it will give you a general idea where to aim.
Since you're catching me on a really great mood today I'll also give you some spoilers discovered after the long hours of GWX Beta Testing.
Pyro Ammunition Ship: Try to hit it under the first mast (from the bow) and it will blow to kingdom come.
Large/Medium Tanker: Aim under of just in front of the first superstructure (again from the bow) and you have one shot kill 9 times out of 10.
Victory/Liberty Cargo: Aim for the second mast (from the bow) and she will go down like a rock.
Auxiliary Cruiser: Aim for bow or aft the gun turret and she will blow to pieces.
Bogue CVE: Aim right under the superstructure (Bridge) and she will blow up.
In all the above set the torpedo runnig depth to 3m except from the tankers where you need to set it to 1m. Pistols always imact of course.
Another important issue is the runnig depth of the torpedoes and the gyro and impact angles. As a rule of thumb always try to have an Angle on the Bow of around 90 deg. The most important thing though is the gyro-angle (the angle theat shows how much the torpedo has to deviate from a straight line in front of the sub). That angle should be around +/- 5 deg. You will know it's good when the little triangle on the cross in your periscope becomes green. The running depth of the torpedo is important as that way you can make sure you hit the flat and not the curved part of the hull. In general anything between 1-3m should produce a huge hole and loads of damage to the ship.
That should do for now. Go out there sink some ships and think what I've suggested. You never know what you might find out
Good Luck and Good Shooting
