Well first if you are going for a 100% realism I recommend doing the Convoy attack in Tutorial, until you can master attacks at close range, also I suggest getting mods that enhance manual targetting such as:
hsGUI v3.1
NeuUzo&PeriV.2
Thomsens Ships V4.1
h.sie's LLRT+SRT+LWS-Combimod V 1.1
those are the ones im using and in my 2nd patrol I sank 1 Ceramic Ocean Type liner, 1 Southampton class & 1 Troop Transport in the same convoy.
Now for night attacks try to use your Observation Persicope "O" since for some reason it has more light than the attack one or if you don't want to risk yourself, use your Hydrophones, as the war advances your hydrophone can send "pings" to other ships to estimate their range, also I'll suggest to always attack in waters with at least 150 meters depth, so you can easily evade the DC from Destroyers, take in mind that realistic reload torpedos take at least 7-11 minutes to load 1 tube.
The more common destroyers escorting convoys have 3~5 meters hull deep, Battleships have 11~14 meters the same goes for high tonnage troop transports, so no need to break your head trying to compare the ship with the recon manual:
Some easy steps
1.- Focus on 2-3 ships in a convoy, then with the mods I mentioned above you can ask one of your officers to manually ID the ship for you
2.- Put the main info in a notebook, like hull deep, speed and range.
3.- Open all your torpedo tubes (Q) and start working on setting your torpedos in the computer (F6).
4.- Rise periscope again and check the heading of the ship
5.- Fix little details and fire all the torpedos to the ships you have already in mind
6.- Proceed to dive, enable silent run and set speed to 1 knot, you can hear everything with your hydrophones so you'll be using them a lot, you can hear the "splash" of the DC's and the sound from your torpedos, the current heading of the destroyers and if their engines are at full-ahead.
Another suggestion is to attempt the single player mission "Troopships", you'll be facing 2 Ocean Liners cruising @ 24 knots perfect for practicing against high speed moving targets.
If you have more questions just ask
