It's important to have all your torps hit at the same time. If I encounter 3 ships in a line, here's my tactic. (...s were necessary to keep the forum posting from shifting my uboat position on me!)
<----< <----< <----<
(ship1) (ship2) (ship3)
..............|
..............| (about 1000 m away)
..........<----<
..........(my firing
...........position)
I get parallel, and point my peri at 90 (when i'm port to them, and 270 if i'm stbd). When fixed on 90, set the tdc to 90 Port (i.e., the AoB when ship2 passes me).
Then in quick order, as ship2 is just about to pass me, I quickly check ship1s range (by sonar if no-one's around), or by a guess, and first a Fast T1 at him out one of the bow tubes, set for 1m below keeldepth. Then I range ship 2 (again, usually a rough guess is fine) and fire a Medium speed T1 at him out another bow tube, depth doesn't matter so long as it will hit. Then I range ship 3 and fire a Slow T1 at him out the stern tube. This usually results in simultaneous hits, because ship 1 and 2 are moving away, so the faster speeds catch up, and since ship 3 is approaching, the slow speed has an advantage.
When attacking convoys, I often do this in reverse - going against the direction of the convoy. The speeds get reversed too (first shot slow, second shot med, third shot out the back end on fast). This is a nice attack because by the time stuff hits, the convoy has run over you and you're already getting behind it.
I remember a line from the Uboat Commander's Handbook - something to the effect of - take advantage of the capabilities of your weapons - use your torpedo's gyro turning ability.
__________________
|