"This convoy must not get through-U-boats pursue, attack and sink." This was the signal that Admiral D nitz sent to the commanders of the 21 U-boats of the Markgraf wolf-pack on September 9, 1941 just before the United States entered the war. Sixty-three merchant ships; a number old and dilapidated and all slow and heavy-laden with vital supplies from the United States for the United Kingdom, were strung out in 12 columns abreast, covering 25 miles...