SM U - 69 SM " U - 69 was a Type U 66 submarine or U - boat for the German Imperial Navy ( ) during the First World War . She had been laid down in February 1914 as U - 10 " the fourth boat of the " U - 7 " class for the Austro - Hungarian Navy ( ) but was sold to Germany , along with the others in her class , in November 1914 . The submarine was ordered as " U - 10 " from Germaniawerft of Kiel as the first of five boats of the " U - 7 " class for the Austro - Hungarian Navy . After the outbreak of World War I in August 1914 , the Austro - Hungarian Navy became convinced that none of the submarines of the class could be delivered to the Adriatic via Gibraltar . As a consequence , the entire class , including " U - 10 " , was sold to the German Imperial Navy in November 1914 . Under German control , the class became known as the U 66 type and the boats were renumbered ; " U - 10 " became " U - 69 " , and all were redesigned and reconstructed to German specifications . " U - 69 " was launched in June 1915 and commissioned in September . As completed , she displaced , surfaced , and , submerged . The boat was long and was armed with five torpedo tubes and a deck gun . As a part of the 4th Flotilla , " U - 69 " sank 31 ships with a combined gross register tonnage of 102 , 875 in five war patrols . " U - 69 " left Emden on her sixth patrol on 9 July 1917 for operations off Ireland . On 11 July , " U - 69 " reported her position off Norway but neither she nor any of her crew were ever heard from again . British records say that " U - 69 " was sunk by destroyer on 12 July , but a German postwar study cast doubt on this . " U - 69 " s fate is officially unknown . Design and construction . After the Austro - Hungarian Navy had competitively evaluated three foreign submarine designs , it selected the Germaniawerft 506d design , also known as the Type UD , for its new " U - 7 " class of five submarines . The Navy ordered five boats on 1 February 1913 . 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 66 cm / 26 ( 2 . 6 in ) deck gun . " U - 10 " was laid down on 7 February 1914 , and her construction was slated to be complete within 29 to 33 months . Neither " U - 10 " nor any of her sister boats 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 , " U - 10 " and her four sisters were sold to the Imperial German Navy on 28 November 1914 . " U - 10 " was renumbered by the Germans as " U - 69 " when her class was redesignated as the Type U 66 . 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 . Service career . " U - 69 " was launched on 24 June 1915 . On 4 September , SM " U - 69 " was commissioned into the " Kaiserliche Marine " under the command of " Kapitänleutnant " Ernst Wilhelms . On 4 March 1916 , " U - 69 " was assigned to the IV . " U - Halbflotille " . " U - 69 " successfully completed five war patrols in which she sank 31 ships with a combined a total of . " U - 69 " s most successful month for number of ships sunk was April 1916 , when she sank eight ships of 21 , 051 tons in a span of six days . The month with the highest tonnage sunk was June 1917 when she sank five ships of 28 , 808 tons in a nine - day span ; nearly half of that total came from one ship , the 13 , 441 - ton British armed merchant cruiser sunk on 14 June . " Avenger " had been patrolling off the Shetland Islands and was returning to Scapa Flow , when she was struck by a single torpedo on the port side . The ship began listing heavily and non - essential crew were evacuated while destroyers arrived and took her under tow . Despite strenuous efforts to save her , " Avenger " foundered ten hours after being hit when her internal bulkheads collapsed . One man was killed in the attack . " U - 69 " began her sixth and final patrol on 9 July when she departed from Emden , destined for operations off Ireland . " U - 69 " s position report at 02 : 30 on 11 July reported that she was south of Lindesnes , Norway , and was the last known contact with " U - 69 " . According to author Dwight Messimer , two British sources report that sank " U - 69 " at position on 12 July . An observer in a kite balloon deployed by " Patriot " spotted a surfaced U - boat at 07 : 00 . The U - boat submerged and " Patriot " hunted the submarine until noon , when it loosed two depth charge s that brought thick brown oil to the surface . A postwar study by Germany cast doubt on whether or not the submarine attacked by " Patriot " was " U - 69 " . Officially , her fate remains unknown . Ships sunk or damaged . < nowiki > * < / nowiki > damaged but not sunk < br >