It was not an easy task to hunt down Kriegsmarine U-boats. The grey wolves of the Atlantic knew precisely when to attack and when to hide from its prey. It was even harder to destroy U-boat pens scattered in the French coasts and the Northern Sea. From the beginning of the war in 1939 through the end of 1942, Allied forces had only neutralized 150 U-boats, roughly three per month. In contrast, the Germans had a success rate of sinking 20 ships of roughly 180,000 tons per month. The British were