SM U - 6 ( Austria - Hungary ) SM " U - 6 or U - VI " was a " U - 5 " - class submarine or U - boat built for and operated by the Austro - Hungarian Navy ( ) before and during the First World War . The submarine was built as part of a plan to evaluate foreign submarine designs , and was the second of three boats of the class built by Whitehead & Co . of Fiume after a design by Irishman John Philip Holland . " U - 6 " was laid down in February 1908 and launched in June 1909 . The double - hull ed submarine was just over long and displaced between , depending on whether surfaced or submerged . " U - 6 " s design had inadequate ventilation and exhaust from her twin gasoline engines often intoxicated the crew . The boat was commissioned into the Austro - Hungarian Navy in July 1910 , and served as a training boat — sometimes making as many as ten cruises a month — through the beginning of the First World War in 1914 . The submarine had only one wartime success , which was sinking a French destroyer in March 1916 . Later that year , in May , " U - 6 " became entangled in anti - submarine net ting deployed as part of the Otranto Barrage . Coming under fire from Royal Navy ' s drifter s running the nets , " U - 6 " was abandoned and sunk . All of her crewmen were rescued and were held in captivity through the end of the war . Design and construction . " U - 6 " was built as part of a plan by the Austro - Hungarian Navy to competitively evaluate foreign submarine designs from Simon Lake , Germaniawerft , and John Philip Holland . The Austro - Hungarian Navy authorized the construction of " U - 6 " ( and sister ship , " U - 5 " ) in 1906 by Whitehead & Co . of Fiume . The boat was designed by American John Philip Holland and licensed by Holland and his company , Electric Boat . " U - 6 " was laid down on 21 February 1908 in the United States , partially assembled , and shipped to Whitehead ' s for final assembly , a process which , author Edwin Sieche notes , " caused a lot of trouble " . She was launched at Fiume on 12 June 1909 . " U - 6 " s design featured a single - hull with a tear - drop shaped body that bore a strong resemblance to modern nuclear submarines . She was long by abeam and had a draft of . She displaced surfaced , and submerged . Her two bow torpedo tubes featured unique , cloverleaf - shaped design hatches that rotated on a central axis , and the boat was designed to carry up to four torpedoes . For surface running , " U - 6 " was outfitted with 2 gasoline engines , but suffered from inadequate ventilation , which resulted in frequent intoxication of the crew ; her underwater propulsion was by two electric motors . Service career . " U - 6 " was commissioned into the Austro - Hungarian Navy on 1 July 1910 , with " Linienschiffsleutnant " Georg Ritter von Trapp in command . Over the next three years she served primarily as a training boat , making as many as ten training cruises per month . On 7 November 1911 , she hosted a Norwegian naval delegation that inspected her . On 26 June 1912 , " U - 6 " was accidentally rammed by the submarine tender " Pelikan " while surfacing after a deep diving trial . At the outbreak of World War I , " U - 6 " was one of only four fully operational U - boats in the Austro - Hungarian Navy fleet , and was stationed at Cattaro by late 1914 . " U - 6 " s activities over the early part of the war are not reported , but the boat ' s armament was augmented by a 3 . 7 cm / 23 ( 1 . 5 in ) quick - firing ( QF ) deck gun in December 1915 . Sister boat " U - 5 " had her first radio receiver installed at the same time her deck gun was added , but it is not reported whether " U - 6 " did , too . On 23 February 1916 , " U - 6 " made an unsuccessful attack on an Italian , but she then managed to torpedo and sink the French destroyer " Renaudin " on 18 March off Durazzo . " Renaudin " went down with 47 of her 83 - man complement . On the night of 12 May , " U - 6 " headed out to try to intercept shipping between Santa Maria di Leuca and Valona . " Linienschiffsleutnant " Hugo von Falkhausen , " U - 6 " s commander since November 1915 , attempted to pass underneath two drifter s that formed a part of the Otranto Barrage . While submerged , von Falkhausen heard an unexplained noise on the hull of the boat , which was likely the sound of " U - 6 " fouling one of the anti - submarine net s deployed from the drifter " Calistoga " . The drifter ' s skipper was alerted to the submarine ' s presence when one of the indicator buoys had fired . " Calistoga " launched signal flares that attracted the attention of two nearby drifters " Dulcie Doris " and " Evening Star II " . In the meantime , von Falkhausen surfaced " U - 6 " to try to cut loose the buoy being dragged behind his boat . When the hatch was opened , the crew discovered the boat entangled in the net . Though unable to submerge , von Falkhausen attempted to flee on the surface , but the port propeller shaft became fouled . Realizing that he was stuck , and with " Dulcie Doris " and " Evening Star II " beginning to shell his boat , " U - 6 " s captain ordered code books and confidential material thrown overboard and the submarine scuttle d . " U - 6 " s three officers and seventeen crewmen were all rescued , but spent the remainder of the war as prisoners of the Italians . In her career , " U - 6 " sank one ship totaling .