Karl Dönitz : biography
Commander of the submarine fleet
On 1 October 1939, Dönitz became a Rear Admiral (Konteradmiral) and "Commander of the Submarines" (Befehlshaber der Unterseeboote, BdU); on 1 September the following year, he was made a Vice Admiral (Vizeadmiral).
With the fall of France, Germany acquired U-Boat bases at Lorient, Brest, St Nazaire and La Pallice/La Rochelle. A communication centre was established at the Chateau de Pignerolles at Saint-Barthélemy-d’Anjou.
By 1941, the delivery of new Type VIIs had improved to the point where operations were having a real effect on the British wartime economy. Although production of merchant ships shot up in response, improved torpedoes, better U-boats and much better operational planning led to increasing numbers of "kills". On 11 December 1941, following Adolf Hitler’s declaration of war on the United States, Dönitz immediately planned for implementation of Operation Drumbeat (Unternehmen Paukenschlag)Commonly known as Drumbeat, it has connotations of "tattoo" or "thunderbolt" in German. This targeted shipping along the east coast of the United States. Carried out the next month with only nine U-boats (all the larger Type IX), it had dramatic and far-reaching results. The U.S. Navy was entirely unprepared for antisubmarine warfare despite having had two years of British experience to draw from, and committed every imaginable mistake. Shipping losses, which had appeared to be coming under control as the Royal Navy and Royal Canadian Navy gradually adapted to the new challenge, skyrocketed.
On at least two occasions, Allied success against U-boat operations led Dönitz to investigate. Among reasons considered were espionage and Allied interception and decoding of German Navy communications (the naval version of the Enigma cipher machine). Both investigations into communications security came to the conclusion espionage was more likely, or else the Allied successes had been accidental. Nevertheless, Dönitz ordered his U-boat fleet to use an improved version of the Enigma machine (one with four rotors, which was more secure than the three-rotor version it replaced), the M4, for communications within the fleet, on 1 February 1942. The German Navy (Kriegsmarine) was the only branch to use this improved version; the rest of the German armed forces (Wehrmacht) continued to use their then-current three-rotor versions of the Enigma machine. The new system was termed "Triton" ("Shark" to the Allies). For a time, this change in encryption between submarines caused considerable difficulty for Allied codebreakers; it took ten months before Shark traffic could be read (see also Ultra codebreaking and Cryptanalysis of the Enigma).
By the end of 1942, the production of Type VII U-boats had increased to the point where Dönitz was finally able to conduct mass attacks by groups of submarines, a tactic he called "Rudel" (group or pack) and became known as "wolfpack" in English. Allied shipping losses shot up tremendously, and there was serious concern for a while about the state of British fuel supplies.
During 1943 the war in the Atlantic turned against the Germans, but Dönitz continued to push for increased U-boat construction and entertained the notion that further technological developments would tip the war once more in Germany’s favour, briefing the Führer to that effect.http://www.militaryhistoryonline.com/wwii/atlantic/bitterend.aspx At the end of the war the German submarine fleet was by far the most advanced in the world, and late-war examples such as the Type XXI U-boat served as models for Soviet and American construction after the war. The Schnorchel (snorkel) and Type XXI boats appeared late in the war because of Dönitz’s personal indifference, at times even hostility, to new technology he perceived as disruptive to the production process.von der Porten, op. cit. His opposition to the larger Type IX was not unique; Admiral Thomas C. Hart, commander of the United States Asiatic Fleet in the Philippines at the outbreak of the Pacific War, opposed fleet boats as "too luxurious".Blair, Silent Victory