On March 1, 1942, a US Navy PBO Ventura sank U-656 off the Canadian coast. For three critical months, the United States had no success against the U-boats, while the East Coast was increasingly unsafe for American ships.
The Germans were winning the battle for production. While new U-boats were being delivered at the rate of thirty each month by June 1942, the Allies lost 173 ships that month alone. Only twenty-one submarines were sunk in the first six months of 1942. The Germans were succeeding in slowly strangling Britain.
The German naval intelligence, B-Dienst, broke the Allied convoy codes, which was part of their success. Fortunately for the Allies, B-Dienst did not discover the Torch convoys bound for North Africa in October-November 1942. Only twenty-three of the more than one thousand transits to North Africa were intercepted and sunk by U-boats.
Even if North Africa could be supplied, the war was lost if Britain were to lose her sea-lanes to the wolf packs. Fortunately for the Allies, Hitler kept siphoning off U-boats from the Atlantic fleet to protect Norway and increase pressure in North Africa. The Norwegian U-boats threatened the North Atlantic supply run to Murmansk and Archangel. In June-July 1942, convoy PQ-17 struggled through U-boats and bombers, losing 69% of the merchantmen when the convoy broke under the threat of the battleship Tirpitz sailing to attack the convoy. The Germans lost five aircraft and sank 183,000 tons.
But the threat from the U-boats in the North Atlantic was the most serious. By March 1943, 400 U-boats were available for attacking convoys between the United States and the United Kingdom; 222 were oceangoing submarines and 114 were on patrol at any given time. The so-called “air gap” —the area where land-based bombers could not patrol—was the U-boats’ favorite killing ground. One hundred and twenty ships were sunk by the end of March, and two-thirds were in convoys. The Royal Navy began to consider the convoy system a failure. Not only would supplies for an invasion not arrive, but Britain might not be able to feed her people or build her own war supplies.
But March 1943 would prove to be the zenith of Nazi submarines. Two new weapons, both the brainchild of the same man, would change the balance of power in favor of the Allies for the rest of the war.
Henry J. Kaiser, an American businessman, recognized the need for mass-produced cargo ships even before America’s entry into the war. His “Liberty” ships, based on British designs, used outdated reciprocating steam engines to save materials and costs, since turbine engines were in limited supply. Design flaws caused several ships to break up in heavy seas. US President Franklin D. Roosevelt called them “Ugly Ducklings.” But they could be built in huge quantities quickly. The first sixty ships built for Britain in September 1941 became a flood of thousands of ships that served on every front. By July 1943, the Americans were building ships far faster than the Germans could sink them.