In RL the Channel was very rarely used by u-Boats after 1939. There are good reasons for that:
- Shallow water
- Close to English ports full of small anti-submarine boats
- Heavily mined by both sides
- Was just as fast to go to the North of the British Isles to get to the Western Approaches and more lucrative from a shipping target perspective.
- After August 1940 the Atlantic ports were available negating the need to come all the way from German ports to get to patrol areas.