I attack 5-7 kms away from convoy. Therefore I always use T1 torpedo. Salvo 4-5 torpedos to convoy, generally hit one or two ships then deep to 150 m and run away, reload of torpedos and attack again.
I only found british carrier with 6 DDs in may 1944 far away of Ireland. I had only one torpedo, attack from 9 kms but missed.