U - 5 - class submarine ( Austria - Hungary ) The " U - 5 " class was a class of three submarine s or U - boats that were operated by the Austro - Hungarian Navy ( ) before and during World War I . The class was a part of the Austro - Hungarian Navy ' s efforts to competitively evaluate three foreign submarine designs . The design of the boats was based upon John Philip Holland ' s submarine design and featured a single , teardrop hull , which resembled the design of modern nuclear submarines . The class members were just over long and displaced surfaced and submerged . All were originally equipped with two bow torpedo tubes and could carry four torpedoes . The first two boats , " U - 5 " and " U - 6 " , built specifically for the Austro - Hungarian Navy , to the same design as the United States C class submarine were partially constructed in the United States and completed at Whitehead & Co . at Fiume . The third was completely constructed by Whitehead ' s at Fiume and purchased by Austria - Hungary to bolster their U - boat fleet after the outbreak of World War I . All three boats had successes during World War I ; between them they sank five ships with a combined tonnage of 22 , 391 . In addition they captured seven ships as prizes and damaged , a French dreadnought of 22 , 189 tons displacement . All three boats were sunk during the war , though " U - 5 " , the lead boat of the class , was raised and recommissioned after her sinking . After the war ' s end , " U - 5 " , the only survivor of the class , was ceded to Italy as a war reparation and was broken up in 1920 . Design and construction . In 1904 , after allowing the navies of other countries to pioneer submarine developments , the Austro - Hungarian Navy ordered the Austrian Naval Technical Committee ( MTK ) to produce a submarine design . The January 1905 design developed by the MTK and other designs submitted by the public as part of a design competition were all rejected by the Navy as impracticable . They instead opted to order two submarines each of designs by Simon Lake , Germaniawerft , and John Philip Holland for a competitive evaluation . The two Holland submarines comprised the " U - 5 " class . The Navy authorized two boats , " U - 5 " and " U - 6 " , from Whitehead & Co . of Fiume in 1906 . The " U - 5 " class was built to the same design as the C class for the US Navy and was built by Robert Whitehead ' s firm of Whitehead & Co . under license from Holland and his company , Electric Boat . Components for the first two Austrian boats were manufactured by the Electric Boat Company and assembled at Fiume , while the third boat was a speculative private venture by Whitehead that failed to find a buyer and was purchased by Austria - Hungary upon the outbreak of World War I . The " U - 5 " class boats had a single - hulled design with a teardrop - shape that bore a strong resemblance to modern nuclear submarines . The boats were just over long and displaced surfaced , and submerged . The torpedo tubes featured unique , cloverleaf - shaped design hatch es that rotated on a central axis . The ships were powered by twin 6 - cylinder gasoline engines while surfaced , but suffered from inadequate ventilation which resulted in frequent intoxication of the crew . While submerged , they were propelled by twin electric motors . The first two boats , " U - 5 " and " U - 6 " , were ordered by the Austro - Hungarian Navy for evaluation and were partially assembled in the United States , shipped to Fiume , and riveted together by Whitehead & Co . , which , author Edwin Sieche reports , " caused a lot of trouble " . " U - 5 " was launched in February 1909 and was followed in June by the launch of " U - 6 " . Both boats were commissioned by April 1910 . The third boat , originally named " SS - 3 " , was built on speculation entirely at Whitehead ' s in Fiume . The boat ' s design featured improvements in the electrical and mechanical systems . Gibson and Prendergast report that , when built , " SS - 3 " was powered by electric motors for both surface and submerged running . When the surface performance of the electric motors proved disappointing in trials , " SS - 3 " s power - plant was rebuilt to match the gasoline / electric combination used in " U - 5 " and " U - 6 " . " SS - 3 " was launched in March 1911 and was offered to the Austro - Hungarian Navy , but because the evaluation of the first two " U - 5 " - class boats was still underway , they declined to purchase . As built , the " U - 5 " - class boats were armed with two bow torpedo tube s and could carry a supply of four torpedoes . By 1915 , all had received a 3 . 7 cm / 23 ( 1 . 5 in ) deck gun . Service career . " U - 5 " and " U - 6 " were both commissioned into the Austro - Hungarian Navy by April 1910 , and served as training boats through 1914 , making as many as ten training cruises per month . During their early years , each boat was demonstrated to a foreign naval delegation ; " U - 5 " to a Peruvian detachment in 1911 , " U - 6 " to a Norwegian group in 1910 . At the beginning of World War I in August 1914 , " U - 5 " and " U - 6 " comprised half of the operational U - boat fleet of the Austro - Hungarian Navy . In the three years after " SS - 3 " s March 1911 launch , Whitehead ' s attempted to sell the boat to the navies of Peru , Portugal , the Netherlands , Brazil , and Bulgaria , before the Austro - Hungarian Navy rejected an offer for the second time . With the outbreak of war , however , the Austro - Hungarian Navy purchased the unsold submarine to quickly bolster its fleet . Although provisionally commissioned as " U - 7 " , she was commissioned as " U - 12 " in August 1914 . By late December 1914 , all three of the " U - 5 " - class boats were based at the naval base at Cattaro and all took part in combat patrols . Between the three boats , they sank five ships with a combined tonnage of 22 , 391 , captured seven ships , and damaged one dreadnought . " U - 6 " was the least successful , sinking a single ship of ; " U - 5 " was the most successful , sinking four ships with of a combined , including the French armoured cruiser " Léon Gambetta " . " U - 12 " damaged , but did not sink , the largest ship torpedoed by any of the " U - 5 " class when she hit the French battleship on 21 December 1914 . Of the three boats of the class , only " U - 5 " survived the war intact . " U - 12 " was sunk with the loss of all hands when she hit a mine near Venice in August 1915 , while " U - 6 " was scuttled by her crew in May 1916 after becoming trapped in an anti - submarine net that was a part of the Otranto Barrage . " U - 5 " herself sank after hitting an Austro - Hungarian mine during a training exercise , but was raised , repaired and recommissioned before the war ' s end . " U - 5 " was ceded to Italy as a war reparation and scrapped in 1920 . Class members . SM " U - 5 " . SM " U - 5 " was laid down in April 1907 and launched in February 1909 . She was commissioned into the Austro - Hungarian Navy in April 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 scored most of her wartime successes during the first year of the war while under the command of Georg Ritter von Trapp . The French armoured cruiser " Léon Gambetta " , sunk in April 1915 , was the largest ship sunk by " U - 5 " . In May 1917 , " U - 5 " hit a mine and sank with the loss of six men . She was raised , rebuilt , and recommissioned , but sank no more ships . At the end of the war , " U - 5 " was ceded to Italy as a war reparation , and scrapped in 1920 . In all , " U - 5 " sank four ships totaling 21 , 604 tons . SM " U - 6 " . SM " U - 6 " was laid down in February 1908 and launched the following June . She served as a training boat after her July 1910 commissioning into the Austro - Hungarian Navy . She served in that capacity through the beginning of World War I in 1914 , making as many as ten training cruises a month . " U - 6 " scored only one wartime success , sinking a French destroyer in March 1916 . In May that same year , she became entangled in anti - submarine net ting deployed as part of the Otranto Barrage . Coming under fire from drifters 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 . SM " U - 12 " . SM " U - 12 " was built on speculation by Whitehead & Co . of Fiume under the name " SS - 3 " . She was laid down in 1909 and launched in March 1911 and featured improvements in the electrical and mechanical systems from the Holland design of her older sister boats , " U - 5 " and " U - 6 " . Whitehead ' s tried selling " SS - 3 " to several different navies , but she was finally bought by the Austro - Hungarian Navy after the outbreak of World War I , despite having been rejected twice before . She was commissioned as " U - 12 " in August 1914 . She sank only one ship during the war , a Greek cargo ship in May 1915 , but had earlier captured six Montenegrin sailing vessels as prizes in March . " U - 12 " also damaged , but did not sink , the French battleship in December 1914 . While searching for targets in the vicinity of Venice in August 1915 , " U - 12 " struck a mine that blew her stern off , and sank with all hands , becoming the first Austro - Hungarian submarine sunk in the war . Her wreck was salvaged the next year by the Italians , who interred the bodies of " U - 12 " s crewmen in a Venetian cemetery .