Same here... dive deep, ahead slow once depth is reached, silent running, zig-zag away from the last ship I hit. I might go flank speed and rudder hard over at the last minute, if a DD seems to be coming right at me.... trying to use the DD's hull noise to mask the maneuver. Timing is tricky on that one though, especially if you're not using the external camera.
There is something I want to try, but haven't had a chance yet -- hiding at shallow depth right underneath an immobilized ship; either one where you've shot out the engines, or a kill that hasn't sunk yet. In theory, the DD's couldn't reach you with depth charges that way, and any active sonar return would be masked by the ship above.
It would be easier getting into position with the external camera, but if it was an actual kill, you'd have a marker on the map and could do it that way. It would suck if the ship did decide to sink while you were under it, but it still sounds like a fun maneuver. Has anyone here tried it?
Your ways are definitely the best. Get deep under the thermal layer (disrupts sonar), Do a "Sprint and Drift" type technique. Don't keep your engines on for more than 10 seconds at a time, then use your forward momentum to drift. Also, right when a DC explodes, go to flank then cut engines. This way your prop sound is makes by the DC's and you get a lot of momentum (enough to travel .2-.3nm)
i would hide under ships in sh3 it works but the dds sometimes will stay around the cripled ship for long periods of time . if you have any torps left you can line the dds up if there circling close to you not shure if it works in sh4 havent had to try yet