Norway opened the route into the Atlantic

The operation depended on the fall of Norway, which opened a sheltered approach along the coast and into the Greenland-Iceland-UK gap beyond the densest British patrols. Limited Coastal Command coverage and the geography of the Norwegian littoral made interception difficult in early 1941. Later in the war, Fairmile D motor gunboats and motor torpedo boats patrolled the Norwegian coast and would have added another close-range threat. Plan Z and the Deutschland-class surface-raider concept could not work against Britain as intended unless Germany first controlled Norway. France's fall then gave the raiders Brest as an escape destination, turning two unexpected German victories into both an Atlantic entrance and a western refuge. Together those conquests overturned the geographic assumptions behind Britain's prewar effort to contain German surface ships in the North Sea.