What role did German U-boats play in the Battle of the Atlantic?

During the Battle of the Atlantic, German U-boats served as the primary weapon in the Third Reich's attempt to sever Britain’s vital maritime supply lines and prevent the Allies from projecting military power across the sea.1

Their role evolved through several distinct phases:

• Early Successes: Initially operating singly, U-boats achieved significant success against unescorted merchant shipping.2
• Wolf Pack Tactics: As the Allies implemented convoy systems, the Germans developed "wolf pack" tactics. In this strategy, a single U-boat would shadow a convoy and summon others via radio to conduct coordinated night attacks on the surface.23
• Expansion and Supply: To extend their reach into remote waters, the Germans utilized "U-tankers"—large submarines designed to refuel and rearm operational U-boats at sea.4
• Technological Adaptation: Late in the war, U-boats were equipped with the snorkel, allowing them to remain submerged longer and avoid radar detection, though this arrived too late to overcome the Allies' overwhelming air and surface superiority.24

Ultimately, the U-boat campaign failed due to Allied advancements in radar, the expansion of the convoy system, and the deployment of long-range aircraft and escort carriers.214