Ive raided Scapa Flow a couple of times in '39 (found an aux. cruiser there
)
and found a really easy way of escaping DDs is to stick really close to the coast and when the DD lines up for a DC attack, theres a good chance that they will run aground.
Bring up the scope and ready stern tube and one less DD on you. Havnt tried this in 40-41 though. I now have over 70,000 GRT to my name and its only November '39