Had a few lessons learned that I found out that worked for "racking up major tonnage".

First the torpedoes. To cut down on the number of misses and duds, during the early years, 41-43, set them to run shallow. If a destroyer draws 10 feet, the shot will often go under it if set at 5-10 feet. So I set them at 1 or 2 feet and get hits.

As for the duds, it is the same as it was in real life. Hit the target broadside and you get a dud, shoot it "down the throat" and it will go off. Most of the time. A favorite tactic of mine is to let the periscope up so the destroyers know where you are and have them come straight at you. Get the angle on the bow close to zero. As long as you aren't being shot at, let the scope up and let him get close. Be going at full speed, let him get to about 500 yards then shoot. I give them one fish then down scope and full right or left rudder to get out of the way.

If one shot doesn't take him out, give him a shot with a stern tube as he goes by. Also, when on the surface, keep the periscope up, you can see targets at a greater range. Big help when you don't have radar.

After the escort are sunk, the others are easier. Also, if you damage a target, stay submerged and get some distance from it. Then go to a depth just deep enough to be able go to the bridge. Then use the deck gun to finish it off. If you get return fire, it only takes a few seconds to get back under.