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.
The second innovation was the escort carrier. Another British design, the escort carrier used a merchant hull outfitted with a flight deck and carried twenty or so planes. Combined with new escorts with new weapons, Allied antisubmarine efforts skyrocketed in success in June 1943. The Canadian Navy went from six vessels in 1939 to almost 1000 ships, mostly frigates designed with shallow drafts to avoid torpedoes. More long-range aircraft, like the B-24 Liberator, were available. The “Hedgehog”— banks of mortars capable of saturating the ocean depths—were sub-killing explosives. Improvements in sonar, combined with better training in coordinated attacks on Wolf Packs, sent the German U-boats to the bottom in record numbers.
In May 1943, convoy SC-130 was attacked by thirty-three U-boats, but suffered no losses and sank five subs. The Germans had lost fifteen U-boats in April, but in May 1943 forty boats were sunk. The U-boat commander, Admiral Karl Dönitz, temporarily pulled back his U-boats in June and losses dropped.
Dönitz hoped the U-boats would benefit by new technologies like the Schnorkel, a breathing tube for the diesel engines that allowed a U-boat to recharge while submerged; acoustic homing torpedoes that would follow the sounds of a ships’ screws; and improved antiaircraft batteries. His submarines returned to the Atlantic, hoping to resupply at sea by using supply submarines called Milch Cows.
The Allies were prepared. Bombers dropped mines outside the U-boat pens, and cracked the concrete bunkers with giant “Tallboy” 14,000 bombs. The Tirpitz was sunk after British midget subs damage its rudder and Lancaster bombers smash it with 22,000 “Grand Slam” bombs. Radar-equipped aircraft flying from escort carriers attack the unsuspecting U-boats at night on the surface. “Foxer”—noise emitters near the propellers—quickly render the acoustic torpedoes ineffective. U-boat losses continue to mount.
Dˆnitz was hoping to stay in the fight long enough to allow the powerful new type XXI and XXIII U-boats, revolutionary designs that would have affected the war if they had been introduced earlier. They did not enter service until April 1945. By then it was too late.
By the time of the surrender in May 1945, U-boats sank 3,500 merchant vessels, 2,452 in the North Atlantic, totaling 18,300,000 aggregate tons, including 175 warships. Tens of thousands of Allied sailors and soldiers rest forever in them. 7500 German sailors, three-fourths of all the Germans who sailed in U-boats, are there too.