Two hints that may help, one philosophical, the other practical:
Shooting a torpedo is a bit like shooting a gun, except in super-slo-motion. If the target is moving, you don't want to shoot where the target is, you want to shoot where the target will be. When you get to a distant contact on the map, if you go to the marker, the target is moving, and so will be long gone by the time you get there. The first thing you want to do with a distant target is establish its possible course and speed, plot that on the map, and then use that as your best guess as to where to go. One of my all-time favorite mods is Wazzoo's Nomograph, which is a tool that turns the mathematics of this business into a simple drawing application.
Click on this link for more:
http://www.paulwasserman.net/SHIII/#...he%20Nomograph
The second piece of advice is to dive your ship and take over the hydrophone controls. Dive, then set the volume of the hydrophone by clicking on the volume knob and drawing the cursor in little circles. Then have the helm go to all stop. Then click on the big dial to move the needle around. If you are within 20 nm or so of a ship, you will hear its screws turning underwater. where the needle is pointing when you hear the screws is the bearing for the target.