Plan Z

Plan Z was the name given to the planned re-equipment and expansion of the Kriegsmarine (German navy) ordered by Adolf Hitler in early 1939. The fleet was meant to challenge the naval power of the United Kingdom, and was to be completed by 1948. Development of the plan began in 1938, but it reflected the evolution of the strategic thinking of the Oberkommando der Marine (Naval High Command) over the two decades following World War I. The plan called for a fleet centered on ten battleships and four aircraft carriers which were intended to battle the Royal Navy. This force would be supplemented with numerous long-range cruisers that would attack British shipping. A relatively small force of U-boats was also stipulated.

When World War II broke out in September 1939, almost no work had been done on the new ships ordered under Plan Z. The need to shift manufacturing capacity to more pressing requirements forced the Kriegsmarine to abandon the construction program, and only a handful of major ships—all of which had been ordered before Plan Z—were completed during the war. Nevertheless, the plan still had a significant effect on the course of World War II, in that only a few dozen U-boats had been completed by the outbreak of war. Admiral Karl Dönitz's U-boat fleet only reached the 300 U-boats he deemed necessary to win a commerce war against Britain in 1943, by which time his forces had been decisively defeated.

Following the end of World War I, the German armed forces became subject to the restrictions of the Treaty of Versailles. For the new Reichsmarine, this meant it was limited to six pre-dreadnought battleships, six old light cruisers, 12 destroyers and 12 torpedo boats. A further two pre-dreadnoughts, two cruisers, and four destroyers and torpedo boats apiece could be kept in reserve. The first major ship to be built after the war was the light cruiser Emden in the early 1920s. This was followed by a further three light cruisers of the Königsberg class: Königsberg, Karlsruhe and Köln, and a further two ships that were modified versions of the Königsberg-class, Leipzig and Nürnberg. At the same time, the Germans created a dummy corporation, NV Ingenieurskantoor voor Scheepsbouw (IvS), in the Netherlands to secretly continue development of submarines. This was in violation of Article 191 of the Treaty of Versailles, which prohibited Germany from possessing or building submarines for any purpose. IvS built several submarines for foreign navies, including the Turkish Gür, which was the basis for the Type I U-boat, and the Finnish Vesikko, which was the prototype for the Type II U-boat.

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