Just a suggestion (possibly mentioned elsewhere?), but I often use the tactic of shooting up a part of convoy, then threading between merchantmen which are going down so as to evade destoyer launched torps/ manouver into position. Tankers and merchantmen to the rear of the convoy often split and go around the sinking vessels, thus becoming more easily picked off. Also, corvettes & destroyers have a hard time of steaming on top of you if you dive under a wrecked vessel. They slow down considerably if they do come through the sea of hulks, and are prone to exposing a nice slow moving flank. Of course, this nautical weaving requires 100% concentration. Don't do what I did once, and enjoy the view for too long as you may steam into a wreck at speed. Glug, glug, glug....
Another string to the collective bow there Dhugs i've used this tactic myself when i feel the need to remind myself how bad it must be to be a tin can driver.
It works very well if you just hang around one of your victims torp'ing all comers. The enemy craft just stay that extra bit away from you!
{edited for typos}
I have used this tactic meself, and have often wondered, which will be especially effective on multi-player, if the sonar is "skewed" or confused
when being used near a wreck. I would think so, especially if the sub is more or less directly underneath wreck?
Also, I have never tried it, but if you are underneath a wreck and it finally
sinks, I would think it would be possible to have the ship going to the bottom hit your ship? Will have to try this in Spectator.