Here is what I do, First I look around before shooting to see if there are any escourts to close. If there is, I turn so all they can see is my stern end, and ahead slow.

Now if there is no one around, and getting in the middle of the convoy is not an option, then I will fire off my front tubes, ahead slow flow with the direction of the convoy ( starbord or port) and keep moving still at periscope depth. If you get far enough from your original postion, you will have the chance to use 1 stern tube (if in XI). If its a hit then I immedatly crash dive, change direction to move away from the convoy (direct opposit direction). Once I get to about 70 - 80 meters I let out a jammer, and go ahead slow, and change my depth to over 100 depending on how deep the water is. Then I change direction of about 15-25 port or stern, then hope for the best. Once I think im in the clear, I will go to periscope depth, and see where the escourt is and what his general search pattern is. If he is in a good spot, I will let out my other eel, and if it misses it misses. (I mostly use megnetics unless its a first attack on a convoy, then it does not exactly matter... Least I dont think it does.)

Hope this helps.