For unrealistic game play w/o mods:
- Use autotargeting.
- Stay clear of destroyers ... as stated above, they react too quickly.
- Get in close ... try never to shoot outside 1500 yards/meters.
- Open the torpedo doors before beginning the attack.
- Lock the target if you don't care how many torps you use ... then use a lot.
- Else, use the scope crosshairs to aim your torpedoes.
- Select auto-reloading.