Karl Dönitz - Inter-war Period

Inter-war Period

The war ended in 1918, but Dönitz remained in a British camp near Sheffield as a prisoner of war until his release in July 1919. He returned to Germany in 1920.

During the interwar period, he continued his naval career in the naval arm of the Weimar Republic's Armed Forces (Reichswehr). On 10 January 1921, he became a lieutenant (Kapitänleutnant) in the new German Navy (Vorläufige Reichsmarine). Dönitz commanded torpedo boats by 1928, becoming a lieutenant-commander (Korvettenkapitän) on 1 November of that same year.

On 1 September 1933, he became a full commander (Fregattenkapitän) and, in 1934, was put in command of the cruiser Emden, the ship on which cadets and midshipmen took a year-long world cruise in preparation for a future officer's commission.

On 1 September 1935, he was promoted to captain (Kapitän zur See). He was placed in command of the 1st U-boat flotilla Weddigen, which included U-7, U-8 and U-9.

During 1935, the Weimar Republic's navy, the Reichsmarine, was replaced by the Nazi German navy, the Kriegsmarine.

Throughout 1935 and 1936, Dönitz had misgivings regarding submarines due to German overestimation of the capabilities of British ASDIC intelligence. In reality, ASDIC could detect only one submarine in ten during exercises. In the words of Alan Hotham, British Director of Naval Intelligence, ASDIC was a "huge bluff".

German doctrine at the time, based on the work of American naval captain Alfred Mahan and shared by all major navies, called for submarines to be integrated with surface fleets and employed against enemy warships. By November 1937, Dönitz became convinced that a major campaign against merchant shipping was practicable and began pressing for the conversion of the German fleet almost entirely to U-boats. He advocated a strategy of attacking only merchant ships, targets relatively safe to attack. He pointed out that destroying Britain's fleet of oil tankers would starve the Royal Navy of supplies needed to run its ships, which would be just as effective as sinking them. He thought a German fleet of 300 of the newer Type VII U-boats could knock Britain out of the war.

Dönitz revived the World War I idea of grouping several submarines together into a "wolfpack" to overwhelm a merchant convoy's defensive escorts. Implementation of wolfpacks had been difficult in World War I owing to the limitations of available radios. In the interwar years, Germany had developed ultra-high frequency transmitters which it was hoped would make their radio communication unjammable, while the Enigma cipher machine was believed to have made communications secure. Dönitz also adopted and claimed credit for Wilhelm Marschall's 1922 idea of attacking convoys using surface or very-near-the-surface night attacks. This tactic had the added advantage of making a submarine undetectable by sonar.

At the time, many – including Admiral Erich Raeder — felt such talk marked Dönitz as a weakling. Dönitz was alone among senior naval officers, including some former submariners, in believing in a new submarine war on trade. He and Raeder constantly argued over funding priorities within the Navy, while at the same time competing with Hitler's friends such as Hermann Göring, who received greater attention at this time.

Since the surface strength of the Kriegsmarine was much less than that of the British Royal Navy, Raeder believed any war with Britain in the near future would doom it to uselessness, once remarking all the Germans could hope to do was to die valiantly. Raeder based his hopes on war's being delayed until the German Navy's extensive "Z Plan", which would have expanded Germany's surface fleet to where it could effectively contend with the Royal Navy, was implemented. The "Z Plan", however, was not scheduled to be completed until 1945.

Dönitz, in contrast, was not constrained by such fatalism but set about intensely training his crews in the new tactics. The marked inferiority of the German surface fleet left submarine warfare as Germany's only naval option once war broke out.

On 28 January 1939, Dönitz was promoted to commodore (Kommodore) and Commander of Submarines (Führer der Unterseeboote).