I have to agree with K-61. Early war between Iceland and England is the best place to hunt. There are a few major convoy routes that run south into England through there. Like K-61 said, mind your depth. I have been caught in the shallows and got some whoopins' that I won't forget.
About 1942, you will start getting reports of Task Forces in the deeper waters between Norway and the English shallows. Patrol off the coast outside of Bergen and you will get some action (not always in your favor).
One thing to note is that starting out the war there is pretty uneventful until it gets closer to Operation Overlord. Once that hits, hold onto your socks because you will be along for a rough ride. The Brits really pick up the ASW ops in the shallows and in the Channel up to, and afterwards.
I have lost several boats to those darn ASW patrols late war in the Channel and north of Scapa Flow...
It's been a rough learning curve.