Not long after Hitler assumed control of Germany's destiny in 1933, the Third Reich laid the foundation of a submarine fleet which it intended should isolate the British Isles when the time came to wipe out the humiliation of 1918. By May, 1945, Germany had built more than 1800 submarines, including midgets, with a total gross tonnage of approximately 1,000,000 tons. But they had not won the war for Hitler.
During World War I the German submarines came very close to starving the British Isles. World War II was a highly mechanized conflict, requiring immeasurably more ship tonnage for the movement of supplies to feed the machines of war as well as the men who operated them.
Germany lost 199 U-boats in World War I. In the recent war she sacrificed 777 underseas boats and over 30,000 men without achieving her objective. The Italian Navy had tried to help out, losing 95 submarines for its trouble.
The U-boat operations in the Atlantic and, with Italian assistance, in the Mediterranean cost the Allies heavily in merchant ships and crews, but they failed to achieve the effectiveness the German admirals had hoped they would.