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.
Dönitz 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.
The Battle of the Atlantic was the decisive battle in the west. UK prime Minister Winston Churchill said in his memoirs, “the only thing that ever really frightened me was the U-boat peril.”