Like you, I use the external camera as I like to see the surface ships at night in a panic after being attacked.
I use high realism and target manually-always. Depending whether I use the XXI or not, I pre target tubes 1-2 to an offset of 20-30 degrees to port and tubes 3-4 to an offset of 20-30 degrees to starboard.
After being picked up by a destroyer or escort and being astern of me, I take a straight line at 1/3 speed and let them pursue. Judging by distance and calculating speed differentials, at about 1-2 minutes depending on how crowded that part of the sea is, I go to flank and throw it over to port or starboard. You can out turn the escorts for the most part. The dangers here to your sub in a maneuver like this are the K guns on the destroyer and whether they have hedgehogs.
If I initially went to to port and the destroyer has passed and overshot me and is now astern or bearing 160 degrees and decreasing, I go to starboard at slow speed and go to the hydrophone station and listen and look at the tactical mode sound trace letting the destroyer / escort approach the bow of my sub at 300-500 meters. Escorts slow to 11 knots to ping you and reacquire as the acoustics are a bit muddied from exploding depth charges.
Since tubes 3-4 are offset to 20-30 degrees to starboard, listen to your hydrophones and look at the sound traces in tactical which are measured. I fire at distances of between 300-400 > meters when they are at about 40 degrees according to the tactical assessment board and is in the " sweet spot. " This allows you to engage the destroyer at the optimal 60-90 degree offset. This also allows for a follow up shot in case you miss. The greater difficulty is the smaller vessels like flower and hunt class ships and especially the armed tugs as the margin for error is greater due to their smaller size. Correct identification is necessary if you set the depth to run under the keel of the ship. With smaller ship like the hunt class, I set my torpedoes for impact and a shallow depth of 1 meter or in the case of not being able to identify the pursuing vessel.
Targeting ships like Merchies that haven't detected you are completely different and you have the fun of calculating speed, distance and angle on the bow. With practice, most can do it and it gives you a fair idea of the challenges that sub commanders faced. SH3 gives you the ability to target manually or automatically letting players grow at their own pace in their abilities.
Give it a shot and enjoy.
