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SM ''U-21'' or ''U-XXI'' was a or U-boat built for and operated by the Austro-Hungarian Navy ((ドイツ語:Kaiserliche und Königliche Kriegsmarine ''or'' K.u.K. Kriegsmarine)) during the First World War. The design for ''U-21'' was based on submarines of the Royal Danish Navy's ''Havmanden'' class (three of which had been built in Austria-Hungary), and was largely obsolete by the beginning of the war. ''U-21'' was just over long and was armed with two bow torpedo tubes, a deck gun, and a machine gun. Construction on ''U-21'' began in mid 1915 and the boat was launched in September 1916. After suffering damage during a diving trial in January 1917, ''U-21'' underwent seven months of repairs before her commissioning in August 1917. The U-boat conducted patrols off the Albanian coast in October 1917, but experienced the failure of the seal on her main hatch. The repairs kept the boat out of action until June 1918. But in July a piston in her diesel engine broke, knocking the submarine out of the rest of the war. At the end of World War I, ''U-21'' was ceded to Italy as a war reparation and scrapped in 1920. ''U-21'' had no wartime successes. == Design and construction == When it became apparent to the Austro-Hungarian Navy that the First World War would not be a short one,〔Halpern, p. 382.〕 they moved to bolster their U-boat fleet by seizing the plans for the Danish ''Havmanden'' class submarines,〔Gardiner, p. 344.〕 three of which had been built at Whitehead & Co. in Fiume.〔 Although the Austro-Hungarian Navy was not happy with the design, which was largely obsolete,〔Halpern, p. 383.〕〔Gardiner, p. 341.〕 it was the only design for which plans were available and which could be begun immediately in domestic shipyards.〔 The Austro-Hungarian Navy unenthusiastically placed orders for ''U-21'' and her three sister boats on 27 March 1915.〔 ''U-21'' was one of two boats of the class to be built at the Pola Navy Yard.〔 Due to demands by the Hungarian government,〔 subcontracts for the class were divided between Hungarian and Austrian firms,〔 and this politically expedient solution worsened technical problems with the design, resulting in numerous modifications and delays for the class in general.〔 ''U-21'' was an ocean-going submarine that displaced surfaced and submerged and was designed for a complement of 18. She was long with a beam of and a draft of . For propulsion, she featured a single shaft, a single diesel engine for surface running, and a single electric motor for submerged travel.〔 She was capable of while surfaced and while submerged. Although there is no specific notation of a range for ''U-21'', the ''Havmanden'' class, upon which the ''U-20'' class was based, had a range of at , surfaced, and at submerged.〔 ''U-21'' was armed with two torpedo tubes located in the front and carried a complement of two torpedoes. She was also equipped with a 66 mm/26 (2.6 in) deck gun and an machine gun.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「SM U-21 (Austria-Hungary)」の詳細全文を読む スポンサード リンク
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