The relative course tool does not work the way you think it does. It's based on the line of bearing to the target, not the direction your u-boat is pointing. Also, the empire bell and explorer classes do look similar at a quick glance. Pay special attention when you encounter one of these so you don't misidentify it in the future. I hope this helps.
When you first determine the course of the ship you plan to attack, why not just place the dot first behind the ship and then before it? This way you won't have to wait. 7:49 Says 20 seconds and hits 5 seconds later? Also, why does the game require you to input the current distance to target? Torpedoes explode on contact, not after a certain distance.
Haha yeah I don't know why it say 20 seconds and then explodes shortly after. The distance is needed however so that the torpedo can travel on an intercept course pretty much. The distance is one of the things that will determine the angle at which the torpedo travels. Hope this helps Stranger!