Formed in 1935, 1st U-Boat Flotilla operated against Hitlers enemies from the very earliest stage of the War through to September 1944 when disbanded amid the flames of Brest (its operating base) during the US siege. Many of the top German naval figures feature in this authoritative history including Karl Donitz, Otto Kretschemmer, Joachim Schepke and Erich Topp. The Flotilla took part in most major operations; the invasions of Norway, Belgium and France and the all-important Battle of the Atlantic. Over 75% of operational U-Boats were lost as the Allies counter-measures and code-breaking successes took ever greater effect. This work records the Flotillas successes and disasters in detail.