The Battle of the Atlantic was a life-and-death struggle between the German Kriegsmarine and the Allied navies that was fought for control of Britain’s lifeline to its empire and to the United States.
Although the Allies triumphed in the end, it was no sure thing. The Germans came very close to knocking the British out of the war. If that had happened, America would have had to fight a two-front war without the huge contributions of the British. Many factors contributed to the eventual outcome. In the end, Allied technical and logistical superiority proved decisive. Perhaps the most intriguing aspect of the long battle was the role played by signals intelligence (SIGINT) on both sides. It is widely known that British codebreakers were ultimately successful in reading the German naval codes. It is less well known that the German codebreakers were also successful for much of the war in reading the British Navy’s coded radio message traffic.
By 1938, the German Navy was deep into planning for war with England. The German naval staff knew that Britain was one of the world’s foremost naval powers. It also knew that Britain could not fight for long without substantial imports of food and raw materials for its war effort, as Britain was not self-sustaining in agricultural products, steel, oil, and other key resources even in peacetime. Its need for these resources would increase substantially during wartime.