German Type U 66 submarine The Type U 66 was a class of five submarine s or U - boat s operated by the German Imperial Navy ( ) during World War I . The class is alternately referred to as the U - 66 " - class or the Type UD . The class was built by Germaniawerft of Kiel to their 506d design as the U - 7 " - class for the Austro - Hungarian Navy . The five boats were sold to the Imperial Germany Navy at the beginning of World War I when it was thought impossible for the submarines to reach the Mediterranean for delivery to Austria - Hungary . The Austro - Hungarian Navy , after competitively evaluating six submarines of three foreign designs , selected the Germaniwerft 506d or Type UD design over a design from Whitehead & Co . for the " U - 7 " class . The boats , numbered " U - 7 " to " U - 11 " , were designed to be long and displace between when surfaced and submerged . They were to be armed with five torpedo tubes and a deck gun . For propulsion the design called for twin diesel engines for surface running and twin electric motors for subsurface movement . The Austro - Hungarian Navy ordered the boats in February 1913 and construction began on the first boats in November . After the outbreak of World War I in August 1914 , the Austro - Hungarian Navy became convinced that delivery of the still - unfinished submarines to the Mediterranean via Gibraltar would be impossible . As a result , they sold the five boats to the Imperial German Navy in November 1914 . The German Navy assigned the numbers " U - 66 " to " U - 70 " to the five submarines and had them redesigned and reconstructed to their specifications . These changes , which included a larger deck gun , increased the displacement of the U - boats by almost surfaced and nearly submerged . All five boats saw active service , and four sank 18 or more ships . Only , sunk six days into her first war patrol in March 1916 , had no successes . Two other boats , and disappeared in 1917 . The remaining two U - boats , and , were surrendered to the United Kingdom and were broken up by 1921 . Background . In 1904 , the Austro - Hungarian Navy , after allowing the navies of other countries to pioneer submarine developments , ordered the Austrian Naval Technical Committee ( ) to produce a submarine design . When the Navy rejected the January 1905 MTK design and other designs submitted as part of a public competition as impracticable , they instead opted to order two submarines each of designs by Simon Lake , Germaniawerft , and John Philip Holland for a competitive evaluation . Based on the trials results , the Austro - Hungarian Navy determined the characteristics that the next generation of Austro - Hungarian submarines should have . They were looking for a double - hulled submarine of about displacement with diesel propulsion . They also wanted a surface speed of between , and for the boat to be armed with between three and five torpedo tubes . The Austro - Hungarian Navy selected the Germaniawerft 506d design , also known as the Type UD , for the " U - 7 " class over the Type 48 design submitted by Whitehead & Co . , primarily because of the lower cost . The Navy ordered five boats on 1 February 1913 . Design . The " U - 7 " class was seen by the Austro - Hungarian Navy as an improved version of its " U - 3 " class , which was also a Germaniawerft design . As designed for the Austro - Hungarian Navy , the boats were to displace on the surface and while submerged . The doubled - hulled boats were to be long ( OA ) with a beam of and a draft of . The Austrian specifications called for two shafts with twin diesel engines ( total ) for surface running at up to , and twin electric motors ( total ) for a maximum of when submerged . The boats were designed with five torpedo tubes ; four located in the bow , one in the stern . The boats ' armament was to also include a single / 26 deck gun . Construction . After the Austro - Hungarian Navy ' s 1 February 1913 order , the first two boats , " U - 7 " and " U - 8 " , were laid down at Germaniawerft on 1 November . " U - 9 " was laid down at the end of December , and the final two boats , " U - 10 " and " U - 11 " were both begun in February 1914 . Construction of the boats was slated to be complete within 29 to 33 months . None of the submarines were complete when World War I began in August 1914 . With the boats under construction at Kiel , the Austrians became convinced that it would be impossible to take delivery of the boats , which would need to be towed into the Mediterranean past Gibraltar , a British territory . As a result , the five boats of the class were transferred to the Imperial German Navy on 28 November 1914 after the advance payment of 2 million Kronen had been returned . Germaniawerft was then awarded " Kriegsauftrag D " , hence the type was known as " UD " . After their purchase , the boats were assigned the numbers " U - 66 " to " U - 70 " , and the class became known as the U 66 type . The Imperial German Navy had the submarines redesigned and reconstructed to German standards , which increased the surface displacement by and the submerged by . The torpedo load was increased by a third , from 9 to 12 , and the deck gun was upgraded from the gun originally specified to an one . " U - 66 " was launched on 22 April 1915 , the first of the class , and was followed by the other four about one every three weeks , with the last boat , " U - 70 " , hitting the water on 20 July . The boats were all completed and commissioned into the Imperial German Navy between July and September . Service career . All the boats of the " U - 66 " class saw active service , and all but one boat , , had wartime successes ; and both sank over 100 , 000 tons of Allied shipping . " U - 68 " was sunk by the British Q - ship in March 1916 , and was the first boat of the class to be lost during the war . " U - 69 " and " U - 66 " were lost in July and September 1917 , respectively . and " U - 70 " both survived the war and were surrendered to the United Kingdom in November 1918 , and both were broken up by 1921 . Class members . SM " U - 66 " . " U - 66 " , the lead boat of the class , was laid down on 1 November 1913 ( yard number 203 ) by Germaniawerft at Kiel and launched on 22 April 1915 . She was commissioned on 23 July 1915 under the command of " Kapitänleutnant " Thorwald von Bothmer . During the war , she sank 25 ships totaling . The two largest ships she sank were the British steamers " Powhatan " ( ) and " Bay State " ( ) , both sunk in 1917 . " U - 66 " was last heard from on 3 September 1917 when she reported her position in the North Sea . Her fate is officially unknown . British records suggest that " U - 66 " may have struck a mine or been sunk by destroyer s , this is not borne out by German records . SM " U - 67 " . " U - 67 " was laid down on 1 November 1913 ( yard number 204 ) by Germaniawerft at Kiel and launched on 15 May 1915 . She was commissioned on 4 August 1915 under the command of " Korvettenkapitän " Erich von Rosenberg - Grusczyski . " U - 67 " sank a total of 18 ships ( ) and damaged a further 3 ( ) . " U - 67 " was surrendered to the United Kingdom on 20 November 1918 and was broken up at Fareham in 1921 . SM " U - 68 " . " U - 68 " was laid down on 31 December 1913 ( yard number 205 ) by Germaniawerft at Kiel and launched on 1 June 1915 . She was commissioned on 17 August 1915 under the command of " Kapitänleutnant " Ludwig Güntzel . Six days into her first war patrol , " U - 68 " encountered the British Q - ship ( Q - ship number five ) off Dingle and was sunk with all hands . " U - 68 " sank no ships during her brief service career . SM " U - 69 " . " U - 69 " was laid down on 7 February 1914 ( yard number 206 ) by Germaniawerft at Kiel and launched on 24 June 1915 . She was commissioned on 4 September 1915 under the command of " Kapitänleutnant " Ernst Wilhelms . During her service career , " U - 69 " sank 31 ships with a combined gross register tonnage of 102 , 875 , the largest among them , the 13 , 441 - ton armed merchant cruiser . " U - 69 " was last heard from on 11 July 1917 when she reported being off the coast of Norway . Her fate is officially unknown , even though British reports credit her sinking to destroyer . The dates in German records , however , do not support this claim . SM " U - 70 " . " U - 70 " was laid down on 11 February 1914 ( yard number 207 ) by Germaniawerft at Kiel and launched on 20 July 1915 . She was commissioned on 22 September 1915 under the command of " Kapitänleutnant " Otto Wünsche . During the war , Wünsche and " U - 70 " sank one warship , the British sloop , and 53 civilian ships totaling . Among the civilian ships was , at , one of the largest ships hit by U - boats during the war . " U - 70 " also damaged four ships of . " U - 70 " was surrendered to the British on 20 November 1918 and was broken up at Bo ' ness in 1919 – 20 .