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SM U-21 was a U-boat built for the Imperial German Navy shortly before World War I. The third of four Type U-19-class submarines, these were the first U-boats in German service to be equipped with diesel engines. ''U-21'' was built between 1910 and October 1913 at the ''Kaiserliche Werft'' (Imperial Shipyard) in Danzig. She was armed with four torpedo tubes and a single deck gun, though a second was added during her career. In September 1914, ''U-21'' became the first submarine to sink a ship with a self-propelled torpedo when she destroyed the cruiser off the Firth of Forth. She also sank several transports in the English Channel and the Irish Sea later in the year, all in accordance with the cruiser rules then in effect. In early 1915, ''U-21'' was transferred to the Mediterranean Sea to support the Ottoman Empire against the Anglo-French attacks during the Gallipoli Campaign. Shortly after her arrival, she sank the British battleships and while they were bombarding Ottoman positions at Gallipoli. Further successes followed in the Mediterranean in 1916, including the sinking of the French armored cruiser ''Amiral Charner'' in February. Throughout 1916, ''U-21'' served in the Austro-Hungarian Navy as ''U-36'', since Germany was not yet at war with Italy and thus could not legally attack Italian warships under the German flag. She returned to Germany in March 1917 to join the unrestricted commerce war against British maritime trade. In 1918, she was withdrawn from front line service and was employed as a training submarine for new crews. She survived the war and sank while under tow by a British warship in 1919. ==Design== ''U-21'' was long overall with a beam of and a height of . She displaced surfaced and submerged. The boat's propulsion system consisted of a pair of 8-cylinder 2-stroke diesel engines manufactured by MAN SE for use on the surface and two electric double motor-dynamos built by AEG for use while submerged. ''U-21'' and her sister boats were the first German submarines to be equipped with diesel engines. The electric motors were powered by a bank of two 110-cell batteries. ''U-21'' could cruise at a top speed of on the surface and submerged. Steering was controlled by a pair of hydroplanes forward and another pair aft, and a single rudder.〔Gröner, p. 4〕 ''U-21'' was armed with four torpedo tubes, which were supplied with a total of six torpedoes. One pair was located in the bow and the other was in the stern. She was initially fitted with a machine gun for use on the surface, but by the end of 1914 this was replaced with a SK L/30 gun. In 1916, a second 8.8 cm gun was added. ''U-21'' had a crew of four officers and twenty-five enlisted sailors.〔Gröner, p. 5〕 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 (Germany)」の詳細全文を読む スポンサード リンク
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