SM U - 31 ( Austria - Hungary ) SM " U - 31 or U - XXXI " was a " U - 27 " class U - boat or submarine for the Austro - Hungarian Navy . " U - 31 " , built by the Hungarian firm of Ganz Danubius at Fiume , was launched in March 1917 and commissioned in April . " U - 31 " had a single hull and was just over in length . She displaced nearly when surfaced and over when submerged . Her two diesel engines moved her at up to on the surface , while her twin electric motors propelled her at up to while underwater . She was armed with two bow torpedo tube s and could carry a load of up to four torpedoes . She was also equipped with a deck gun and a machine gun . In October 1917 , " U - 31 " sank while in port at Porto Bergudi and was out of service through April 1918 while she was raised and repaired . During her service career , " U - 31 " sank two ships and damaged one warship , sending a combined tonnage of to the bottom . " U - 31 " was at Cattaro at war ' s end and was awarded to France as war reparation in 1920 , towed to Bizerta and scrapped there . Design and construction . Austria - Hungary ' s U - boat fleet was largely obsolete at the outbreak of World War I . The Austro - Hungarian Navy satisfied its most urgent needs by purchasing five Type UB I submarines that comprised the from Germany , by raising and recommissioning the sunken French submarine " Curie " as , and by building four submarines of the that were based on the 1911 Danish " Havmanden " class . After these steps alleviated their most urgent needs , the Austro - Hungarian Navy selected the German Type UB II design for its newest submarines in mid 1915 . The Germans were reluctant to allocate any of their wartime resources to Austro - Hungarian construction , but were willing to sell plans for up to six of the UB II boats to be constructed under license in Austria - Hungary . The Austro - Hungarian Navy agreed to the proposal and purchased the plans from AG Weser of Bremen . " U - 31 " displaced surfaced and submerged . She had a single hull with saddle tank s , and was long with a beam of and a draft of . For propulsion , she had two shafts , twin diesel engines of for surface running , and twin electric motors of for submerged travel . She was capable of while surfaced and while submerged . Although there is no specific notation of a range for " U - 31 " in " Conway ' s All the World ' s Fighting Ships , 1906 – 1921 " , the German UB II boats , upon which the " U - 27 " class was based , had a range of over at surfaced , and at submerged . " U - 27 " - class boats were designed for a crew of 23 – 24 . " U - 31 " was armed with two bow torpedo tube s and could carry a complement of four torpedoes . She was also equipped with a 75 mm / 26 ( 3 . 0 in ) deck gun and an machine gun . After intricate political negotiations to allocate production of the class between Austrian and Hungarian firms , " U - 27 " was ordered from Ganz Danubius on 12 October 1915 . She was laid down on 4 July 1916 at Fiume and launched on 20 March 1917 . Service career . After undergoing trials at Fiume during March , " U - 31 " made a training voyage to Brioni in April . On 24 April 1917 , SM " U - 31 " was commissioned into the Austro - Hungarian Navy under the command of " Linienschiffsleutnant " Franz Nejebsy . Nejebsy , a 32 - year - old native of Teplitz - Schönau , Bohemia ( present - day Czech Republic ) , had previously served two stints as commander of . " U - 31 " departed from Pola on 29 May to patrol along the Adriatic coast of Italy and returned on 5 June . " U - 31 " departed for a patrol in the Mediterranean on 19 June . After a problem with a pump required a stop at Brioni , the U - boat continued on . Nejebsy launched a torpedo attack on an armed yacht west of Strovathi on 25 June , but the torpedoes missed their mark . " U - 31 " ended her patrol at Cattaro after ventilation problems kept the temperature in the engine room from falling below . After a month of repairs at Cattaro , " U - 31 " headed out on another patrol on 6 August . On each of the next two days the U - boat had to crash dive to avoid bombing attacks by French airplanes , the second day ' s attack damaging the boat slightly . On 10 August , Nejebsy and " U - 31 " scored their first kill with the sinking of am Italian cargo ship . The 4 , 021 - ton " Lealta " was carrying ammunition from Syracuse to Malta when " U - 31 " intercepted her in the Ionian Sea east of Malta . An escorting destroyer dropped a pattern of ten depth charge s over " U - 31 " . The following day , Nejebsy was maneuvering " U - 31 " into position to attack a convoy when the U - boat was rammed from behind by a destroyer . " U - 31 " s periscope was hit and twisted by the impact , forcing Nejebsy to end his attack and " U - 31 " s patrol . On the way back to Cattaro , " U - 31 " was attacked by an aircraft in the Straits of Otranto , but reached the safety of the port on 15 August . " U - 31 " was assigned to patrol the Austro - Hungarian and Albanian coasts over the next six weeks . She headed to Fiume via Spalato on 16 October , reaching there three days later . On 26 October " U - 31 " sank from an unknown cause in the harbor at Porto Bergudi . When raised from her resting depth of the next day , one crewman was found alive inside the boat . " U - 31 " was taken first to the Danubius shipyard at nearby Fiume , and , later , on to Pola for repairs and trials . In January , while " U - 31 " s repairs were still ongoing , Nejebsy was reassigned , leaving the U - boat without a commander for the next three months . On 11 March " Linienschiffsleutnant " Hermann Rigele was transferred from the helm of to assume command of " U - 31 " . Rigele , who had been born in Sarajevo , was 26 years old and had also been in command of and , before that , at age 25 . Rigele and " U - 31 " departed Pola on 30 April for a three - day cruise to Cattaro via Sebenico . On 20 May , the boat left Cattaro for a Mediterranean patrol , but had to turn back with leaks after a day . In June , the Austro - Hungarian Navy planned an assault on the Otranto Barrage , similar to a May 1917 action that evolved into the Battle of Otranto Straits . " U - 31 " was deployed from Cattaro on 9 June in advance of the attack . One of the seven separate groups participating in the attack — dreadnoughts and — came under attack from Italian MAS torpedo boats in the early morning hours of 10 June . " Szent István " was hit and sank just after 06 : 00 , and the entire operation was called off . " U - 31 " returned to Cattaro on 12 June . On 16 June , Rigele and " U - 31 " again set out for a Mediterranean patrol , but had to immediately return with clutch problems . Two days later , the U - boat set out again for the Mediterranean . The next day , 19 June , Rigele had to take the boat to a depth of to avoid a depth charge attack . On 7 July , Rigele stopped the Italian sailing vessel " Giuseppino Padre " and , using explosive charges , sank the 67 - ton ship . " U - 31 " ended her patrol at Cattaro on 10 July . Over the next two months , the submarine operated in the Adriatic out of Cattaro and Pola , patrolling off Durazzo and the Albanian coast . After the Armistice with Bulgaria on 29 September ended Bulgaria ' s participation in the war , Durazzo gained importance to the remaining Central Powers as the main port for supplying their forces fighting in the Balkans . Anticipating this , the Allies put together a force to bombard Durazzo . While the second echelon of the attacking force got into position to shell the town , " U - 31 " and sister boat , both patrolling off Durazzo , maneuvered to attack . Although " U - 29 " was blocked by screening ships and experienced a heavy depth charge attack , " U - 31 " was able to get in position to launch torpedoes at the British cruiser . One of them hit its mark and blew the stern off of " Weymouth " , killing four sailors in the process . The other British cruisers involved in the attack took the damaged " Weymouth " under tow and departed . United States Navy submarine chaser s were involved in the depth charge attacks on " U - 29 " and " U - 31 " and erroneously claimed that they had sunk both of the submarines . " U - 31 " was able to make her way back to Cattaro on 6 October . Over the next three weeks , " U - 31 " patrolled between Cattaro and Antivari , Montenegro . After her arrival back at Cattaro on 26 October , she remained there until she was awarded to France as a war reparation in 1920 . " U - 31 " was towed , along with sister boats " U - 29 " and , from Cattaro for scrapping at Bizerta . In total , " U - 31 " sank two ships with a combined tonnage of 4 , 088 , and damaged one warship . Ships sunk or damaged . < nowiki > * < / nowiki > damaged but not sunk