Austro - Hungarian U - boat classes The Austro - Hungarian U - boat fleet during the First World War mainly consisted of German manufactured units transported by rail from Germany ' s northern shipyards to the Austrian ports on the Adriatic Sea . They served throughout the war against Italian , French and British shipping in the Mediterranean Sea with some success , losing eight of the twenty eight boats in service in return . Following the end of the war in 1918 , all Austrian submarines were surrendered to the Entente powers , who disposed of them individually . As both Austria and Hungary became landlocked in the aftermath of the war , no Austrian or Hungarian submarines ( or any other naval vessels ) have been commissioned since . In some sources Austro - Hungarian U - boats are referenced with Roman numerals as a way to distinguish them from German U - boats with similar numbers , but the Austro - Hungarian Navy itself used Arabic numerals . There are gaps in the numbering for several reasons . One series of Austro - Hungarian U - boats under construction in Germany was sold and commissioned into the Imperial German Navy . In other cases , U - boats commissioned into the Imperial German Navy were temporarily assigned Austro - Hungarian numbers when they operated in the Mediterranean . One final reason , in the case of the unassigned " U - 13 " , was superstition . This is a list of all U - boats commissioned into the Austro - Hungarian Navy . ( Submarines on which construction was begun but which were not completed or commissioned during World War I are not included . ) " U - 1 " class . The " U - 1 " class consisted of two submarine s or U - boats named " U - 1 " and " U - 2 " , which were built for and operated by the Austro - Hungarian Navy . The " U - 1 " - class boats were built to an American design at the navy yard in Pola . The class was a part of the Austro - Hungarian Navy ' s efforts to competitively evaluate three foreign submarine designs . The two " U - 1 " - class boats , both launched in 1909 , were long and as built were each powered by two gasoline engines while surfaced , and two electric motors when submerged . Neither boat was operational at the beginning of World War I because both were in drydock awaiting replacement diesel engines for their problematic gasoline engines . Beginning in 1915 , both boats conducted reconnaissance cruises out of either Trieste or Pola until declared obsolete in early 1918 . Both remained in service as a training boats at the submarine base on Brioni , but each was at Pola at the end of the war . They were ceded to Italy as war reparations in 1920 and scrapped at Pola . Neither submarine sank any ships during the war . " U - 3 " class . The " U - 3 " class consisted of two U - boats , " U - 3 " and " U - 4 " , and was also a part of the Austro - Hungarian Navy ' s efforts to competitively evaluate three foreign submarine designs . The " U - 3 " - class boats were designed and built by Germaniawerft of Kiel , Germany . During the evaluations conducted by the Navy , the " U - 3 " design bested the " U - 1 " ( Lake ) and " U - 5 " ( Holland ) classes in reliability and provided the best living conditions . They did , however , have the worst diving abilities of the three designs , and produced excessive exhaust smoke . The two " U - 3 " - class boats , both launched in 1908 , were just under long and were each powered by two kerosene two - stroke engine s while surfaced , and two electric motors when submerged . The " U - 3 " class initially had diving problems that were alleviated after several modifications to fins and diving plane s . Both boats of the class served in combat during World War I . , the lead boat of the class , was sunk by gunfire in August 1915 . was the longest - serving Austro - Hungarian submarine and sank over of ships , including the Italian armored cruiser " Giuseppe Garibaldi " in July 1915 . " U - 4 " was handed over to France as a war reparation in 1920 and scrapped . " U - 5 " class . The " U - 5 " class consisted of three U - boats , " U - 5 " , " U - 6 " , and " U - 12 " , and was also a part of the efforts of Austro - Hungarian navy to competitively evaluate three foreign submarine designs . The design of the boats was based upon John Philip Holland ' s submarine design and the boats featured a single , teardrop - shaped 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 , 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 , sinking five ships with a combined gross register tonnage ( GRT ) of 22 , 391 . In addition they captured seven ships as prizes and damaged a French dreadnought of . 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 surviving example of the class , was ceded to Italy as a war reparation and was broken up in 1920 . " U - 10 " class . The " U - 10 " class was a class of five U - boats — " U - 10 " , " U - 11 " , " U - 15 " , " U - 16 " , and " U - 17 " — of the Austro - Hungarian Navy during World War I . The class was similar to the German Type UB I submarine of the German Imperial Navy ( ) . The boats were small coastal submarines that displaced surfaced and submerged . The first two boats delivered to Austria - Hungary had previously been commissioned in February 1915 by the Kaiserliche Marine , while the remaining three were commissioned by the Austro - Hungarian marine in April 1915 . The " U - 10 " class as a whole did not have much wartime success , with three of the boats sinking either one or no ships . Only one boat , sank more than of enemy ships . Of the five submarines of the class , only was sunk during the war ; the remaining four were delivered as war reparations and broken up by 1920 . " U - 14 " class . SM " U - 14 or U - XIV was a U - boat of the Austro - Hungarian Navy during World War I . She was launched in 1912 as the French Curie " ( Q 87 ) , but captured and rebuilt for service in the Austro - Hungarian Navy . At war ' s end , the submarine was returned to France and restored to her former name . " Curie " was launched in July 1912 at Toulon and completed in 1914 . She measured just under long and displaced nearly on the surface and just over when submerged . At the outbreak of World War I in August 1914 , " Curie " was assigned to duty in the Mediterranean . In mid - December , " Curie " s commander conceived a plan to infiltrate the Austro - Hungarian Navy ' s main base at Pola , but during the 20 December attempt , the vessel became ensnared in harbor defenses . Two Austro - Hungarian ships sank " Curie " , killing three of her crew ; the remainder were taken prisoner . The Austro - Hungarian Navy , which had a small and largely obsolete U - boat fleet , immediately began salvage efforts and succeeded in raising the lightly damaged submarine in early February 1915 . After a refit , the boat was commissioned as SM " U - 14 " in June , but had little success early in her career . When her commander fell ill in October , he was replaced by Georg Ludwig von Trapp . " U - 14 " was damaged by a depth charge attack in February 1916 , and underwent an extensive modernization through November . Resuming duty under von Trapp , " U - 14 " sank her first ship in April 1917 , but had her most successful patrol in August , when she sank five ships — including , reportedly the largest cargo ship in the world — in a six - day span . In January 1918 , von Trapp was replaced as commander , but neither of his two successors were able to match his accomplishments . In all , " U - 14 " sank 11 ships with a combined gross register tonnage of nearly 48 , 000 tons . Returned to France at the end of the war , she rejoined the French Navy in July 1919 under her former name of " Curie " . She was stricken in 1928 and scrapped in 1929 . " U - 20 " class . The U - 20 " class was a class of four U - boats , " U - 20 " , " U - 21 " , " U - 22 " , and " U - 23 " . The class is sometimes referred to as the Havmanden " class because it was based upon the design of the Royal Danish Navy ' s 1911 " Havmanden " class submarines , three of which were built in Fiume . Even though the " Havmanden " - class design was largely obsolete by the beginning of the war , four boats were ordered by the Austro - Hungarian Navy in 1915 , in part because construction could begin immediately . Political considerations caused the order to be split between Austrian and Hungarian firms , which contributed to construction problems and delays , keeping any of the boats from being operational until mid - 1917 . The class boats were just over than long and were armed with two front torpedo tubes , a deck gun , and a machine gun . The engines for the boats were unreliable , which compounded handling problems with the design . The " U - 20 " class did not claim any wartime successes , yet lost two of the boats — " U - 20 " and " U - 23 " — to enemy action during the war . The remaining two were delivered as war reparations and broken up . The conning tower from " U - 20 " , which was raised and salvaged in 1962 , is on display in a military museum in Vienna . " U - 27 " class . The " U - 27 " class was a class of eight U - boats — " U - 27 " , " U - 28 " , " U - 29 " , " U - 30 " , " U - 31 " , " U - 32 " , " U - 40 " , and " U - 41 " — based upon the German Type UB II design of the German Imperial Navy and was constructed under license in Austria - Hungary . After the Austro - Hungarian Navy had filled its most urgent needs for submarines after the outbreak of World War I , they selected the German Type UB II design for its next group of submarines in mid - 1915 . Orders for the first six boats were placed in October 1915 with the Austrian firm of Cantiere Navale Triestino and the Hungarian firm of Ganz Danubius . Two more boats were ordered in 1916 , bringing the class total to eight . The boats were just over long and were armed with two bow torpedo tubes , a deck gun , and a machine gun . For propulsion they were equipped with twin diesel engines for surface running and twin electric motors for subsurface movement . Although the class was based on the German design , the Austro - Hungarian U - boats were heavier and slightly faster underwater , but less heavily armed than their German counterparts All eight boats were commissioned into the Austro - Hungarian Navy between 1917 and 1918 and saw active service during the war . and were the most successful in terms of ships sunk and gross register tonnage sunk , respectively . Two boats sank only one ship each , and a third , , sank no ships . " U - 30 " was also the only boat of the class to be lost during the war . The remaining seven were ceded to France and Italy as war reparations and six were scrapped by 1920 ; the seventh sank while being towed to Bizerta for scrapping . " U - 43 " class . The " U - 43 " class was a class of two coastal U - boats which were Type UB II submarines — " U - 43 " , and " U - 47 " — of the Imperial German Navy , making the two classes identical . From the beginning of World War I , Austria - Hungary had been working to increase the size of its U - boat fleet , so the Imperial German Navy , which was finding it difficult to obtain trained submarine crews , sold two of its UB II boats , and , to its ally in June 1917 . The German Type UB II design incorporated improvements over Type UB I boats , the first coastal submarines of the German Imperial Navy . Among these were twin engines and shafts for more redundancy during operations , a higher top speed , and larger torpedo tubes with double the complement of torpedoes . As a result the UB II boats were nearly twice as heavy as their predecessor UB I boats . Both boats of the class were selected for German service in the Mediterranean while under construction . They were shipped via rail to Pola , assembled , launched , and commissioned in the German Imperial Navy , where both enjoyed great success against Allied shipping . In June 1917 , the boats were decommissioned , handed over to Austria - Hungary , and then commissioned into the Austro - Hungarian Navy in July . The " B " in the designation of both boats was dropped , but the submarines retained the same numbers , becoming " U - 43 " and " U - 47 " under the Austro - Hungarian flag . At the end of the war and were ceded to Italy and France , respectively , and had been scrapped by 1920 . Other classes . Several other classes were designed , but none of these ended up being operated by the Austro - Hungarian navy . The Type U 66 was a class of five U - boats operated by the German Imperial Navy ( ) during World War I . The class is alternately referred to as the U - 66 " - class or the Type UD . The class was built by Germaniawerft of Kiel to their 506d design as the U - 7 " - class for the Austro - Hungarian Navy . The five boats were sold to the Imperial Germany Navy at the beginning of World War I when it was thought impossible for the submarines to reach the Mediterranean for delivery to Austria - Hungary . The Austro - Hungarian Navy , after competitively evaluating six submarines of three foreign designs , selected the Germaniwerft 506d or Type UD design over a design from Whitehead & Co . for the " U - 7 " class . The boats , numbered " U - 7 " to " U - 11 " , were designed to be long and displace between when surfaced and submerged . They were to be armed with five torpedo tubes and a deck gun . For propulsion the design called for twin diesel engines for surface running and twin electric motors for subsurface movement . The Austro - Hungarian Navy ordered the boats in February 1913 and construction began on the first boats in November . After the outbreak of World War I in August 1914 , the Austro - Hungarian Navy became convinced that delivery of the still - unfinished submarines to the Mediterranean via Gibraltar would be impossible . As a result , they sold the five boats to the Imperial German Navy in November 1914 . The German Navy assigned the numbers " U - 66 " to " U - 70 " to the five submarines and had them redesigned and reconstructed to their specifications . These changes , which included a larger deck gun , increased the displacement of the U - boats by almost surfaced and nearly submerged . The " U - 48 " class was a class of four U - boats planned for the Austro - Hungarian Navy ( ) during World War I . The design of the boats was based on plans purchased from the German firm of AG Weser in January 1916 . The Navy authorized Cantiere Navale Triestino to begin construction of the submarines in Pola in September 1916 . Only two of the planned four boats were laid down , but both of them were never launched or completed . Both incomplete submarines were scrapped after the war ended . The " U - 50 " class was a class of four ocean - going U - boats planned for the Austro - Hungarian Navy ( ) during World War I . The design of the boats was based on the Project 835 design purchased from the German firm of Germaniawerft in July 1915 . The Navy authorized Ganz Danubius to begin construction of the submarines in Fiume in February 1916 . Only two of the planned four boats were laid down , but neither were ever launched or completed . The two incomplete submarines were scrapped after the war ended . The " U - 52 " class was a class of four ocean - going U - boats planned for the Austro - Hungarian Navy ( ) during World War I . The submarine design was based on the A 6 proposal submitted by Stabilimento Tecnico Triestino ( STT ) as part of a Navy design competition . STT , under its wartime name of Austriawerft , began construction on the first two boats in 1916 , but neither boat was launched or completed before the end of the war . Both incomplete submarines were scrapped after the war ended . Neither of the third and fourth submarines was ever laid down . The " U - 101 " class was a class of nine U - boats planned for the Austro - Hungarian Navy ( ) during World War I . The class was based on the Type 1916 S 1 design from Ungarische Unterseebotsbau AG . The first three boats were laid down in late 1917 and early 1918 by Austriawerft in Trieste , but none were launched or completed before the end of the war . None of the other six submarines was ever laid down . The " U - 107 " class was a class of U - boats planned for the Austro - Hungarian Navy ( ) during World War I . The design was similar to the Germaniawerft UD design which had formed the basis for the Austro - Hungarian Navy ' s s . Two boats ( " U - 107 " and " U - 108 " ) were laid down in early 1918 by Ganz Danubius in Fiume , but neither was launched or completed before the end of the war . No other submarines of the class were ever laid down .