type submarine boat german_imperial_navy german kaiserliche_marine world war laid february fourth boat class german und sold germany class november submarine ordered boats class outbreak world war august austro hungarian navy convinced submarines class delivered adriatic gibraltar consequence entire class including sold german_imperial_navy november german control class known type boats renumbered redesigned reconstructed german specifications launched june commissioned september completed displaced tonnes long tons surfaced tonnes long tons submerged boat metres long armed torpedo tubes deck gun 4th flotilla sank ships combined gross register war patrols left sixth patrol july operations ireland july reported position norway crew heard british records sunk destroyer july german postwar study cast doubt fate officially unknown design construction austro hungarian navy evaluated foreign submarine designs selected design known type new class submarines navy ordered boats february class seen improved version class design designed boats displace tonnes long tons surface tonnes long tons submerged doubled boats metres long overall beam metres draft metres austrian specifications called shafts twin diesel engines metric horsepower total surface running knots mph twin electric motors shp total maximum knots mph submerged boats designed torpedo tubes located bow stern boats armament include single deck gun laid february construction slated complete months sister boats complete world war began august boats construction kiel austrians convinced impossible delivery boats need towed mediterranean past gibraltar british territory result sisters sold imperial_german_navy november renumbered germans class redesignated type imperial_german_navy submarines redesigned reconstructed german standards increased surface displacement tonnes long tons submerged tonnes long tons torpedo load increased deck gun upgraded gun originally specified service career launched june september commissioned imperial_german_navy command march assigned successfully completed war patrols sank ships combined total gross register tons grt successful month number ships sunk april sank ships tons span days month highest sunk june sank ships tons day span nearly half total came ship ton british armed merchant cruiser sunk june patrolling returning scapa_flow struck single torpedo port ship began listing heavily non essential crew evacuated destroyers arrived took tow despite efforts save hours hit internal bulkheads collapsed man killed attack began sixth final patrol july departed destined operations ireland position report july reported nautical miles south norway known contact according author british sources report sank position july observer balloon deployed patriot spotted surfaced boat boat submerged patriot hunted submarine noon depth charges brought thick brown oil surface postwar study germany cast doubt submarine attacked patriot officially fate remains unknown summary raiding history
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