Tactics, tips and tricks.

[Hangman]

I have discovered, at least from 39' through most of 40', if you put an eel into a merchant being escorted, you can dive under the merchant without much hassle at all.
A fine example; I was watching patiently to a small convoy moving across my path from port to starboard. I was idling along at 1 knot, aligning an eel to hit the 9k merchant some 800 meters away, and another to hit the far column. Two escorts, one aft of the convoy some 4500 meters out, the other taking the lead. The sun had a pleasant 20 degree angle from the horizon and the seas were relatively calm, perhaps a 2. I set the first eel to run slow and about 2.5 meters deep. The latest intel reported the eels running 6+ meters deeper than they were set so I was playing it. The second eel was to run faster, thus clearing the first merchant before the strike hit.
The fish left the tubes with a whoosh of air and the boat bobbed a bit from the sudden weight loss. We sat quietly watching the escorts for possible detection but they were oblivious to our presence. Well, ... until the pair of incredible explosions that were less than 10 seconds apart that is. Talk about timing, it was fenominal.
At any rate, the rear escort came charging in my direction so I dropped the scope, ordered 30 meter depth and 20 degrees to starboard, ahead slow. We were now roughly 700 meters from the merchant I just hit. He was laboring hard to keep the ship moving and by the time the escort arrived at where the fish had come from and started their search, I was just about to go under the first merchant and crawl toward the second who was hit. The escorts continued searching on the merchants starboard side as that is where the fish had come from. I meandered over to the port side of the two merchants who were now dead in the water, aligned my boat, cleared the other two tubes, watched them hit, and then headed in the direction the convoy came from, into the setting sun.

There were plenty of DC's, but not a one came close so I was in no hurry to get anywhere fast.
By the time the escorts gave up on me, the convoy was long gone. I couldn't even pick them up on the hydrophones. The sun had set and tubes were reloaded with fresh eels eager to go out and play.

If I'm close enough (500 to 900 meters) I almost always go under the ships I have torpedoed. Lots of times they are going too fast and I don't get to hit them again immediately, but the wounded ships will always wait for me.
If I'm too far out (1200 to 1800 meters) when I hit the merchants, I immediately head in the direction the convoy came from, quickly opening the distance between us. The farther away the convoy gets, the less time the escorts have to search for you. And of course I employ what was mentioned earlier, go deep, listen intently, gun it when you must.

I know they won't drop DC's close to the convoy ships, so if you have a wounded merchant crawling along at 3-4 knots, even though you are not running silent, you can sit at 25-30 meters deep and keep the merchant above you (I lift my scope just enough to see under the water and look for the bottom of the wounded merchant). After dark or when the escorts are a decent distance from me, I turn 180 degrees, go deep and leave them all behind.