German submarine U - 703 German submarine " U - 703 " was a Type VIIC U - boat of the German Kriegsmarine deployed during the Second World War against allied shipping in the Arctic Ocean . She was a successful boat , which had a far longer service life than most other U - boats , primarily due to the restricted zone of operations in which she fought . Her main mission during the war was to target the Arctic Convoys which carried supplies to the Soviet Union from Britain . At this she was quite successful in her three years of raiding until her presumed demise in 1944 . " U - 703 " was built at Hamburg in Northern Germany on the North Sea . She was completed in the autumn of 1941 , and given to the experienced Kptlt . Heinz Bielfeld to command . He took her on her working - up period in which the boat was tested and the crew trained in the Baltic Sea and around the German held coastlines , before being dispatched to Narvik in Norway for her first war patrol in April 1942 . War Patrols . Enjoying the improving Arctic weather , " U - 703 " had an unsuccessful patrol in terms of victims , but the boat began to work better as a team , and the second patrol in May reaped dividends , with the sinking of the 6 , 000 ton American freighter SS " Syros " . This ship sank with eleven lives after a torpedo touched off her ammunition . The same patrol scored greater success during the disastrous end to Convoy PQ - 17 on the 5 May , when she managed to sink two lone cargo ships , one of them damaged by long range German bombers beforehand . Returning to port at Narvik , " U - 703 " was cheered by her victory , but she struggled to make further impressions during the year , as her two further patrols yielded only one victim , the British destroyer , which was fatally crippled by a torpedo near Convoy PQ - 18 in September . Following her lay - over in the winter as her home ports of Narvik , Trondheim , Hammerfest , Harstad and Bergen were all frozen , " U - 703 " returned to the offensive , again attacking allied convoys in the Arctic Sea . Her first two patrols , in January and April were short and barren , but on the next two in July and August 1943 under her new commander Joachim Brünner , she cruised in Soviet waters in the Barents Sea and further east , catching a small Soviet armed trawler on 1 August , and larger Soviet merchant ship the next day , sinking the SS " Sergj Kirov " near Istvestij Island . These patrols had shown the vulnerability of older U - boats to newer allied countermeasures and protection , forcing the submarines to divert themselves into backwaters of the Battle of the Atlantic in order to gain any victories . The " U - 703 " continued operating in the spring of 1944 , but she was obviously less efficient and was given duties deploying weather balloons in the Arctic Sea to test weather conditions for reports to other shipping . This was in part a result of terrible damage she received off Narvik during her first patrol of the season , when allied aircraft strafed her , killing three crew and wounding three more . Just a few days before she had claimed her only victim of the year , the SS " Empire Tourist " , which was sunk whilst part of Convoy RA - 57 . Relegated to her new duties , " U - 703 " suddenly disappeared around the 25 September 1944 . She had left Narvik on her thirteenth war patrol on 14 September , in order to deploy a weather balloon in the Arctic . At the time a heavy gale was running , and it has been assumed that " U - 703 " foundered due to heavy seas in the course of this difficult and highly technical operation . No trace of the boat and her 54 crew has ever been found .