The Norwegian was a medium cargo wasn't it? They are difficult to sink with one torpedo even when legitimate targets. Try hitting them with a magnetic pistol (0.5m below keel) at the No. 3/4 hold position and you'll have more one-shot success. This tends to cause uncontrollable flooding aft and drags them down slowly by the stern. Not dramatic but it works.
95% of my patrols are in Type II's in the North Sea and English Channel approaches, the density of coastal shipping (once you get to know the sailing lanes) means you'll be out of torpedoes very quickly and sometimes have several different encounters on the same day. Nine or ten ships (half by gunfire) in one short patrol is not uncommon once you've got the hang of it.
Be wary of any single ships heading W or SW, more than likely it'll be a neutral. I have found a good position is 40-60 km offshore just about anywhere along the East Coast to intercept the north-south traffic between the Firth of Forth and the Thames Estuary. AN55 is a particularly rich fishing ground and has some patches of deeper water too but you'll have to accept being in shallower water most of the time. The area east of Flamborough Head is a 'convoy junction' from January 1940 onwards.
The flak gun is good for the small fry (anything under 1200 tons
except large trawlers so long as you get
very close and aim at waterline) and if you listen on the 'phones yourself you'll be surprised how much activity there is going on around you. They may not appear to be individually worthwhile but when you've sunk four or five the tonnage starts to add-up.
No long boring patrols like one can get stuck with in the Atlantic and from November 1939 the coastal convoys start to appear.
KH