You should open your torpedo door (press the Q key to do this) before you fire. The time between your pressing of the firing button and the torpedo actually leaving the sub is much smaller this way. More importantly, your "firing solution" is set at the time you hit the firing button. The several second delay while the torpedo tube opens, throws off your firing solution so that you will often hit further astern of (possibly even missing the ship entirely) the point you're aiming at. Opening the tube beforehand avoids this problem.

I do that, but WTF is up with not being able to open more than one tube at a time??I usually always fire two torps at a ship, sometimes more.

I should be ableto open more than one tube..

On another note..

how many people that do shoot atleast 2 torps use impact and magnetic as a combination?

That's what salvos are for. Just set it up the way you need it, then when you open doors, the ones you are using will open.

alternatively, you can go into the conning tower, and find a row of switches on the wall in roman numerals, you can flick those switches to open all your torpedo tubes then you can fire away.

Penelope_Grey's got the right advice here. Just an additional warning. When you have a torpedo tube selected, then select another one, the door to the first torpedo tube automatically closes (Doesn't matter whether you opened it with the Q key or the switches). So, when using Penelope's method, make sure you have made all the torpedo adjustments (depth, impact/magnetic) you want and that the selected tube is for the FIRST torpedo that you want to fire. Then open the doors with the switches on the wall.

You can also use the equivalent switches in the control room above the plotting table.

I play with WO assist on and My procedure is usually as follows:

1. Get into as good a firing position as you can. I always try to get as close to 90 degree AOB firing from within 1200m and almost always use impact torps set at between 2 and 5 metres depending on target and weather. I never use salvoes as I like to reset my solutions between shots. I use the WO solutions to know when the AOB and distance are right.
2. Open the tubes by hitting Q.
3. Select the firing point on the target using UZO or Periscope and request a solution from the WO.
4. Fire first tube and hit Y to select the next tube.
5. Open the next tube using Q.
6. Repeat steps 3, 4 and 5 until I'm happy I've fired enough to sink the target

In most cases two or three torps is enough but sometimes only one. I usually fire the first shot at the midship section just forward of the target's funnel or bridge depending on the class of ship. This is usually where fuel bunkers or engine rooms are located and in most cases will slow or stop the target.

2nd and if necessary 3rd shots go to the bow or stern unless it is a BB. Then I aim below the turrets to try to hit the magazines. If I'm onto a stopped BB, I might go magnetic with one or two shots and impact on the others.

One type of torpedo not mentioned is the homing torp. Remember to avoid any high speed runs when one of these eels is in the water. They may turn back on you if you are the noisiest target in the area. Aiming with these is less of an issue as they will turn towards the maker of the biggest noise along the inital bearing of the shot.