This book is an in-depth study of the U-boat section of the German navy, which came so very close to bringing Britain to its knees during the Battle of the Atlantic in 1941-2. It looks at pre-war German efforts to buildup and reinvigorate the U-boat theory of war, consulting hitherto lightly-researched material in the Bundesarchiv, and the U-Boat Diary during the war. It follows the clandestine U-boat research of the 1920s and early 1930s, and the effects of the assumption of power by the Nazi Party in 1933. It investigates Doentiz's early career and his subsequent efforts to run the U-boat arm during the Second World War. It does not stop here; it will constitute a thorough new look at the entire U-boat campaign from the start of the war through to the final days, and points out the moments when fortunes changed for both sides.