Early in the war you can get away with many harbour raids as long as you are patient, quiet and pick a harbour that is not enclosed in narrow bay. In Hartlepool you can always score C2s and tankers. The only problem is that those darn T2s just wont sink...
(not the best targets for TypII boats).
Anyway, you can even survive Dover (for a while at least) long enough to score the early C2s. Hartlepool and Portland are my favorites regarding routes in and out of.