May 1943. The month Germany lost the Atlantic in 22 days. In the first three weeks of May 1943, German U-boats sank 34 Allied merchant ships in the North Atlantic. In the same three weeks, they lost 41 submarines of their own. For four years, Karl Dönitz had been winning the war at sea. His wolfpack tactics had nearly starved Britain into surrender. In March 1943, U-boats sank 120 ships, and the British Admiralty privately concluded that the convoy system itself might no longer be viable. Then everything turned at once. Centimetric radar arrived on escort ships and patrol aircraft. Submarines that surfaced at night to recharge their batteries, the standard wolfpack tactic, were now visible from 30 miles away through fog and darkness. American escort carriers closed the "mid-Atlantic gap," the patch of ocean previously beyond land-based air cover. Very long range B-24 Liberators flew patrols from Iceland. HF/DF radio direction finders, nicknamed "Huff-Duff," triangulated a U-boat's position the moment it radioed home. Bletchley Park read those messages in near real time. Convoy SC 130 sailed in mid-May. Not a single merchant ship was lost. Six U-boats were sunk. On May 19, 1943, U-954 was depth-charged in the North Atlantic by the British escorts HMS Jed and HMS Sennen. All 47 crew died. Among them was Oberleutnant zur See Peter Dönitz, age 21. Karl Dönitz's son. Five days later, on May 24, Admiral Dönitz signaled every U-boat in the North Atlantic to withdraw. He wrote in his war diary, "We have lost the Battle of the Atlantic." He would lose his second son, Klaus, exactly one year later, in May 1944. Klaus was not supposed to be aboard the torpedo boat that night. He had volunteered, against orders, to celebrate his 24th birthday with the crew. The boat was sunk by British destroyers off Selsey Bill. By the end of the war, three out of every four men who ever sailed in a U-boat were dead. It was the highest casualty rate of any service arm of any nation in the Second World War.