Editing Karl Dönitz (section)

==Interwar period==
He continued his naval career in the naval arm of the [[Weimar Republic]]'s armed forces. On 10 January 1921, he became a {{lang|de|[[Kapitänleutnant]]}} (lieutenant) in the new German navy ({{lang|de|[[Vorläufige Reichsmarine]]}}). Dönitz commanded [[torpedo boat]]s, becoming a {{lang|de|[[Korvettenkapitän]]}} (lieutenant-commander) on 1 November 1928. On 1 September 1933, he became a {{lang|de|[[Fregattenkapitän]]}} (commander) and, in 1934, was put in command of the cruiser [[German cruiser Emden|''Emden'']], the ship on which cadets and midshipmen took a year-long world cruise as training.{{sfn|Williamson|2007|p=10}}

In 1935, the {{lang|de|[[Reichsmarine]]}} was renamed {{lang|de|[[Kriegsmarine]]}}. Germany was prohibited by the [[Treaty of Versailles]] from possessing a submarine fleet. The [[Anglo-German Naval Agreement]] of 1935 allowed submarines and he was placed in command of the U-boat flotilla {{lang|de|Weddigen}}, which comprised three boats; {{GS|U-7|1935|2}}; {{GS|U-8|1935|2}} and; {{GS|U-9|1935|2}}. On 1 September 1935, he was promoted to {{lang|de|[[Kapitän zur See]]}} (naval captain).{{sfn|Williamson|2007|p=10}}

Dönitz opposed Raeder's views that surface ships should be given priority in the {{lang|de|Kriegsmarine}} during the war,{{sfn|Terraine|1989|pp=345–348}} but in 1935 Dönitz doubted U-boat suitability in a naval trade war on account of their slow speed.{{sfn|Terraine|1989|pp=186–188}} This phenomenal contrast with Dönitz's wartime policy is explained in the 1935 Anglo-German Naval Agreement. The accord was viewed by the navy with optimism, Dönitz included. He remarked, "Britain, in the circumstances, could not possibly be included in the number of potential enemies."{{sfn|Terraine|1989|p=187}} The statement, made after June 1935, was uttered at a time when the naval staff were sure [[France]] and the [[Soviet Union]] were likely to be Germany's only enemies.{{sfn|Terraine|1989|p=187}} Dönitz's statement was partially correct. Britain was not foreseen as an immediate enemy, but the navy still held onto a cadre of imperial officers, which along with its Nazi-instigated intake, understood war would be certain in the distant future, perhaps not until the mid-1940s.{{sfn|Terraine|1989|p=187}}

Dönitz came to recognise the need for more of these vessels. Only 26 were in commission or under construction that summer. In the time before his command of submarines, he perfected the group tactics that first appealed to him in 1917. At this time Dönitz first expressed his procurement policies. His preference for the submarine fleet was in the production of large numbers of small craft. In contrast to other warships, the fighting power of the U-boat, in his opinion, was not dependent on its size as the torpedo, not the gun, was the machine's main weapon. Dönitz had a tendency to be critical of larger submarines and listed a number of disadvantages in their production, operation and tactical use.{{sfn|Terraine|1989|pp=196–197}} Dönitz recommended the [[Type VII submarine]] as the ideal submarine. The boat was reliable and had a range of {{convert|6,200|nmi|km|abbr=off}}. Modifications lengthened this to {{convert|8700|nmi|km|abbr=off}}.{{sfn|Terraine|1989|pp=197–198}}

Dönitz revived [[Hermann Bauer]]'s idea of grouping several submarines together into a {{lang|de|Rudeltaktik}} ("pack tactic", commonly called "wolfpack") to overwhelm a merchant convoy's 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, (ukw) while the [[Enigma cipher machine]] was believed to have made communications secure.{{sfn|Rohwer|2015|pp=3–4, 257–262}} A 1922 paper written by {{lang|de|Kapitäinleutnant}} Wessner of the {{lang|de|Wehrabteilung}} (Defence Ministry) pointed to the success of surface attacks at night and the need to coordinate operations with multiple boats to defeat the escorts.{{sfn|Westwood|2005|pp=55–56}} Dönitz knew of the paper and improved the ideas suggested by Wessner.{{sfn|Haslop|2013|p=51}} This tactic had the added advantage that a submarine on the surface was undetectable by [[ASDIC]] (an early form of [[sonar]]). Dönitz claimed after the war he would not allow his service to be intimidated by British disclosures about ASDIC and the course of the war had proven him right.{{sfn|Terraine|1989|p=188}} In reality, Dönitz harboured fears stretching back to 1937 that the new technology would render the U-boat impotent.{{sfn|Westwood|2005|pp=53–54}} Dönitz published his ideas on night attacks in January 1939 in a booklet called {{lang|de|Die U-Bootwaffe}} which apparently went unnoticed by the British.{{sfn|Milner|2011|p=17}} The Royal Navy's overconfidence in Asdic encouraged the Admiralty to suppose it could deal with submarines whatever strategy they adopted — in this they were proven wrong; submarines were difficult to locate and destroy under operational conditions.{{sfn|Milner|2011|p=17}}

In 1939 he expressed his belief that he could win the war with 300 vessels.{{sfn|Terraine|1989|p=215}} The Nazi leadership's rearmament programme prioritised land and aerial warfare. From 1933 to 1936, the navy was granted only 13 per cent of total armament expenditure.{{sfn|Overy|2002|p=182}} The production of U-boats, despite the existing [[Plan Z|Z Plan]], remained low. In 1935 shipyards produced 14 submarines, 21 in 1936, 1 in 1937. In 1938 nine were commissioned and in 1939 18 U-boats were built.{{sfn|Westwood|2005|pp=53–54}} Dönitz's vision may have been misguided. The British had planned for contingency construction programmes for the summer, 1939. At least 78 small escorts and a crash construction programme of "[[Whaler|Whale catchers]]" had been invoked. The British, according to one historian, had taken all the sensible steps necessary to deal with the U-boat menace as it existed in 1939 and were well placed to deal with large numbers of submarines, prior to events in 1940.{{sfn|Milner|2011|pp=16–17}}