Heading changes are a must to avoid DDs. I prefer to man the hydrophones myself when i see one is closing in (i have map updates on), this way i can hear the exact time where his RPM goes up.
That means he's starting his attack run and he's probably mostly deaf as a result of all his noise. What he does is use the last fix on your position, go over it at high speed and start dropping depth charges.
At that point you can safely go to flank speed for 10-15 seconds (some people say as far as 30 seconds, but i won't push my luck), then drop back to silent speed. Also, you can go to flank speed for a short amount of time when an escort is pinging
but only against a single escort. They can't both ping and listen at the same time, so since he's pinging and using an active detection method you might as well get some speed to maneuver with and put some distance between you. Against multiple escorts this won't work though, since there's always one available to listen. More on this later.
By going flank when he's deaf, you achieve two things.
First one is separation. If you go silent before he starts listening again, you'll have put some valuable meters between your actual position and the last position known to the DD. After 2-3 times of this, he'll be DCing empty water 200m behind you, because he hasn't got an updated fix on you.
Second one is the ability to maneuver the boat at high rudder deflection without losing too much speed. If you are at silent speed and you turn the rudder all the way, your speed will drop to 1kt. So, when you can go flank you should also turn hard to point your stern to the DD. I prefer not to point the bow to a DD at all. It has a similar profile as the stern as far as detection goes, but it means i might run through a string of DCs he dropped.
There are however cases where you just can't go flank at all. This is usually when 2-3 escorts are working together. One will be listening, the second will be listening or pinging (they can't do both at the same time) and the third one will make a pass on you using the triangulated data the other two provide him. Then they will rotate positions, with two of them detecting you and the third one making a run.
In that case you must do your absolute must to remain silent, even if he's pinging. I wouldn't go to higher speeds in this scenario, unless he's directly over me and i my crew says he's dropping DCs. If it comes to that, make a hard turn at flank speed, change depth and pray. At all other times against multiple escorts, i prefer to creep along silently, deeply and use small rudder changes to zig-zag when he's dropping over me, or turn to point my stern at him and make his pinging less effective. No more than 20-30 degrees of rudder though, so that my speed doesn't drop too much. It's all a compromise between achieving separation (speed), presenting a low profile (maneuvering, which limits speed) and noise (which increases with speed).
Mind you, that's all for GWX. Your boat will be easier to turn hard without losing speed in the stock game, so you could probably stay silent all the time against multiple escorts and use full rudder deflection as well when necessary.
Another thing to do when you start gaining some distance and he seems to have lost you, is draw a 2km circle on the nav map, point your stern to the DD and exit the circle at silent speed. I don't know how GWX modifies sensors, but i think that in the stock game maximum detection range of a DD was about 2 kms. I don't remember if this is for active (pinging) or passive detection though.
Hope it helps
