The Sunderland and other patrol aircraft are more effective when they can concentrate on the North Sea rather than search the whole Atlantic. German submarines would need to remain submerged more often, cutting speed and range before they even begin an Atlantic patrol. A mine barrier, fighter protection, and aircraft rotating between British and Norwegian bases could maintain near-continuous surveillance. Surface raiders face the same geography: aircraft, submarines, torpedo boats, destroyers, and blocking capital ships make the Skagerrak and North Sea dangerous exit routes.
Chapter · 45:42-51:50
A North Sea barrier constrains U-boats and raiders
Patrol aircraft, fighters, mines and Norwegian bases could turn the North Sea into a barrier that drains U-boat endurance and exposes German capital ships before they reach the Atlantic.