France and Norway reshape the Atlantic battle

Geography shaped the operational problem in the Atlantic. The timing of the First and Second Happy Times reflected access to bases and transit routes as well as torpedoes and tactics. French Atlantic ports moved German bases roughly 450 miles west, spared U-boats the long transit around the United Kingdom, and increased both fuel efficiency and time on station. British control of the shallow, mined English Channel still constrained movement, while control or friendly neutrality in Norway could have created a much stronger northern barrier. Once Norway fell, submarines gained an easier route into the North Atlantic and Arctic convoys lost a measure of geographic protection. The campaign depended on bases and sea routes as much as on the ships themselves.