Screw tutorial videos that make it too complicated.
1. Lock onto a ship
2. Identify it, use the filters if you must. 90% of the time its a Liberty Cargo, Hog island type A, Cimmeron tanker or Fletcher destroyer.
3. Use the stadimeter on the mast with the flag to identify the range, this works best with darkwraiths UI mod, but its close enough
4. Angle on bow, the hardest part.
you are determining your position from the perspective of the ship you are attacking, use the angle tool, draw a line in the direction he is heading by first clicking in front of the contact, than dragging a line across his "tail" to make a paralell line to the target. after this drag the "Arm" onto your submarine, you will get a reading such as "45 degrees left" or "85 degrees right". Enter this into the computer.
5. Speed, you can guess this from experiance or just click the contact in the tactical map
6. Launch the torpedo. Practice and you'll be nailing them in no time. At first dont attack targets faster than 12 knots or farther away than 1200 meters. With experiance you can shoot faster targets farther away.
Good hunting. If you didnt understand anything in this guide i would be happy to explain more. Please ask. Automatic shooting is for bitches.