Ahoy..
My approach, with either a merchie convoy or even a Task force, is the same approach & has worked well enough for Me. Get within 7,000 (or 4,000 if in an S boat...), on as parallel a course as possible with maybe a slight 5 degree in bound slip added in, ahead of them.. set up the fish, accordingly to what I know is the targets (I keep a pad to make notes on what the composition of the targets is.. noted on what ship is where.. & lil' tidbits of draft read on them). Using that info, then setting the fish accordingly. Once that is done, then dive & then open all tubes, and wait a bit to allow them to begin to pass by til I feel they are where I want them to be.. & let fly with the torps.
Once the last torp has left the tube.. I drop scope, & claw for the depths on a 10 degree course headed a bit off & away from where I launched from..
After that, prepared to dodge if I have to, any escorts that might by chance head that direction... I play it by ear, after that as to how I proceed from there to reattack, or slip out away, surface & run out ahead to reacquire & reattack if needed. Just depends on how the initial attack pans...
How I do that, has worked fairly well so far. Have been a couple of targets, that limped off to lick their wounds.. but, not very many.
M. M.
Of note, I do use auto targeting.. figure use the crew.. is what a skipper would do.. use all his available resources to make an attack...