The Grey Wolves: Echoes from WWII S01 E01 The Killing Begins

In the early years of the Second World War, the elite force of German submariners known as the Ubootwaffe came perilously close to perfecting the underwater tactics of the First World War and successfully cutting Britain's transatlantic lifeline. In 1940, the U-boats started to take a real toll against merchant shipping, credited with sinking 2,606,000 tons of shipping.