Up to 1943, with the German capital ships blockaded and ineffective, the Germans were nonetheless winning the war at sea: their U-boat arm had already sunk 12 million tons of merchant shipping. In the month of November 1942 alone they sank 117 ships, comprising 700,000 tons. Meanwhile the Allies' best technological minds devised instruments and techniques to pinpoint and destroy the predators. From May 1943 the hunters became the hunters and the odds shortened on…