SM UB - 12 SM " UB - 12 " was a German Type UB I submarine or U - boat in the German Imperial Navy ( ) during World War I . The submarine disappeared in August 1918 . " UB - 12 " was ordered in October 1914 and was laid down at the AG Weser shipyard in Bremen in November . " UB - 12 " was a little under in length and displaced between , depending on whether surfaced or submerged . She carried two torpedo es for her two bow torpedo tube s and was also armed with a deck - mounted machine gun . " UB - 12 " was broken into sections and shipped by rail to Antwerp for reassembly . She was launched and commissioned as SM " UB - 12 " in March 1915 . " UB - 12 " spent her entire career in the Flanders Flotilla and sank 22 merchant ships , about half of them British fishing vessels . The U - boat was also responsible for sinking the British destroyer in 1917 . By early 1917 , " UB - 12 " had been converted into a minelayer with the replacement of her torpedo tubes with four mine chutes . " UB - 12 " disappeared after 19 August 1918 . Design and construction . After the German Army ' s rapid advance along the North Sea coast in the earliest stages of World War I , the German Imperial Navy found itself without suitable submarines that could be operated in the narrow and shallow seas off Flanders . Project 34 , a design effort begun in mid - August 1914 , produced the Type UB I design : a small submarine that could be shipped by rail to a port of operations and quickly assembled . Constrained by railroad size limitations , the UB I design called for a boat about long and displacing about with two torpedo tube s . " UB - 12 " was part of the initial allotment of seven submarines — numbered to — ordered on 15 October from AG Weser of Bremen , just shy of two months after planning for the class began . " UB - 12 " was laid down by Weser in Bremen on 7 November . As built , " UB - 12 " was long , abeam , and had a draft of . She had a single Körting 4 - cylinder diesel engine for surface travel , and a single Siemens - Schuckert electric motor for underwater travel , both attached to a single propeller shaft . Her top speeds were , surfaced , and , submerged . At more moderate speeds , she could sail up to on the surface before refueling , and up to submerged before recharging her batteries . Like all boats of the class , " UB - 12 " was rated to a diving depth of , and could completely submerge in 33 seconds . " UB - 12 " was armed with two torpedo es in two bow torpedo tube s . She was also outfitted for a single machine gun on deck . " UB - 12 " s standard complement consisted of one officer and thirteen enlisted men . After work on " UB - 12 " was complete at the Weser yard , she was readied for rail shipment . The process of shipping a UB I boat involved breaking the submarine down into what was essentially a knock down kit . Each boat was broken into approximately fifteen pieces and loaded on to eight railway flatcar s . In February 1915 , the sections of " UB - 12 " were shipped to Antwerp for assembly in what was typically a two - to three - week process . After " UB - 12 " was assembled and launched on 2 March , she was loaded on a barge and taken through canals to Bruges where she underwent trials . Early career . The submarine was commissioned into the German Imperial Navy as SM " UB - 12 " on 29 March 1915 under the command of " Kapitänleutnant " ( " Kapt . " ) Hans Nieland , a 29 - year - old first - time U - boat commander . On 18 April , " UB - 12 " joined the Flanders Flotilla ( ) , which had been organized on 29 March . When " UB - 12 " joined the flotilla , Germany was in the midst of its first submarine offensive , begun in February . During this campaign , enemy vessels in the German - defined war zone ( ) , which encompassed all waters around the United Kingdom , were to be sunk . Vessels of neutral countries were not to be attacked unless they definitively could be identified as enemy vessels operating under a false flag . On 24 July , Nieland and " UB - 12 " sank four British fishing vessels while patrolling between east - northeast of Lowestoft . All four of the sunken ships were smack s — sailing vessels traditionally rigged with red ochre sails — which were stopped , boarded by crewmen from " UB - 12 " , and sunk with explosives . " UB - 12 " similarly sank a pair of smacks off Lowestoft on 4 August , and another trio from 23 to 25 August . On 21 November , Nieland was succeeded by " Oberleutnant zur See " ( " Oblt . " ) Wilhelm Kiel in command of " UB - 12 " . Under Kiel ' s command , " UB - 12 " sank three ships on 21 February 1916 : the 100 - ton Belgian fishing ship " La Petite Henriette " , the largest sunk to - date by " UB - 12 " , and another pair of British smacks , " Oleander " and " W . E . Brown " . " UB - 12 " sank her largest ship , " Silksworth Hall " of , on 10 April . The British - registered ship was en route from Hull to Philadelphia in ballast when Kiel torpedoed her without warning a little more than one nautical mile ( two kilometers ) from the Corton Lightvessel . Other ships picked up 31 survivors from " Silksworth Hall " , but 3 men were lost . Later in the month , Admiral Reinhardt Scheer , the newest commander - in - chief of the High Seas Fleet , called off the merchant shipping offensive and ordered all boats at sea to return , and all boats in port to remain there . Grand Fleet ambush attempts . In mid - May , Scheer completed plans to draw out part of the British Grand Fleet . The German High Seas Fleet would sortie for a raid on Sunderland , luring the British fleet across nests ' of submarines and mine - fields " . In support of the operation , " UB - 12 " and five other Flanders boats set out at midnight 30 / 31 May to form a line east of Lowestoft . This group was to intercept and attack the British light forces from Harwich , should they sortie north to join the battle . Unfortunately for the Germans , the British Admiralty had intelligence reports of the departure of the submarines which , coupled with an absence of attacks on shipping , aroused British suspicions . A delayed departure of the German High Seas Fleet for its sortie ( which had been redirected to the Skagerrak ) and the failure of several of the U - boats stationed to the north to receive the coded message warning of the British advance caused Scheer ' s anticipated ambush to be a " complete and disappointing failure " . In " UB - 12 " s group , only " UB - 10 " sighted the Harwich forces , and they were too far away to mount an attack . The failure of the submarine ambush to sink any British capital ships allowed the full Grand Fleet to engage the numerically inferior High Seas Fleet in the Battle of Jutland , which took place 31 May – 1 June . " Kapitänleutnant " Georg Gerth took command of " UB - 12 " on 26 June , after " Oblt . " Kiel was assigned to command the new minelaying submarine . Two months later , Admiral Scheer set up another ambush for the British fleet with plans for another High Seas Fleet raid on Sunderland ( as had been the original intention in May ) . The German fleet planned to depart late in the day on 18 August and shell military targets the next morning . As in May , " UB - 12 " was part of a group intended to attack the Harwich forces . As one of five boats forming the second line of boats from the Flanders Flotilla , " UB - 12 " was stationed off Texel by the morning of 20 August . Once again , British intelligence had given warning of the impending attack and ambush , causing the Grand Fleet to sortie at 16 : 00 on 18 August , five hours before the German fleet sailed . Faulty intelligence caused Scheer initially to divert from Sunderland , and then to eventually call off the whole operation . Although U - boats to the north sank two British light cruisers , " UB - 12 " and her group played no part in the action . In September , Gerth led " UB - 12 " in sinking two more ships and capturing a third ship as a prize . The 313 - ton Norwegian steamer " Rilda " was sunk on 6 September , while the 55 - ton " Marjorie " was sunk on the 28th . In between the Dutch ship " Niobe " was seized as a prize on the 7th . Conversion to minelayer . " UB - 12 " and three sister boats — " UB - 10 " , " UB - 16 " , and " UB - 17 " — were all converted to minelaying submarines . " UB - 12 " was at the dockyard from November 1916 to January 1917 , and it is likely the boat was converted during this timeframe . The conversion involved removing the bow section containing the pair of torpedo tubes from each U - boat and replacing it with a new bow containing four mine chutes capable of carrying two mines each . In the process , the boats were lengthened to , and the displacement increased to on the surface , and below the surface . During this same time , " Kapt . " Gerth was transferred to , and replaced on " UB - 12 " by " Oblt . " Friedrich Moecke in early November . Moecke was , in turn , replaced by " Oblt . " Ernst Steindorff in January 1917 . By March , the newly converted submarine had begun laying mines off the French coast . The French Navy trawler " Elisabeth " struck one of " UB - 12 " s mines off Calais on 13 March and sank . Five days later , the British auxiliary minesweeper " Duchess of Montrose " sank with a loss of 12 men after detonating a mine laid by " UB - 12 " off Gravelines . On 23 March , , a destroyer with the Dover Patrol , struck one of " UB - 12 " s mines off Cape Gris - Nez and went down with the loss of 59 men . In May , " UB - 12 " was on a patrol with in the English Channel . On the night of 14 / 15 May while " UB - 12 " was on the surface , Steindorff noted a large underwater explosion some miles away in a British minefield , and when " UB - 39 " failed to return to Zeebrugge , one of the bases for the Flanders Flotilla , reported what was likely the demise of " UB - 39 " at the hands of a British mine . April found two more victims added to " UB - 12 " s tally . On the 20th , " Nepaulin " , another British auxiliary minesweeper was lost on one of " UB - 12 " s mines near the Dyck Lightvessel . Six days later , the British steamer " Alhama " was mined while loaded with pit prop s destined for Dunkirk . The 1 , 744 - ton cargo ship was the largest ship sunk by " UB - 12 " since the " Silksworth Hall " , sunk the previous April . " UB - 12 " sank another two ships under Steindorff ' s command , one each in June and July . The steamer " Dulwich " — carrying coal from Seaham for London — was mined and sunk with the loss of five men on 10 June . One month later , the French patrol vessel " Jupiter I " was mined off Calais . These were the last two ships credited to mines from " UB - 12 " for the next fourteen months . Fate . " UB - 12 " s activities over the next year are not well documented , and no specific record of her can be found in English - language sources . However , it is known that during this period , she was helmed by four different commanders , with the final officer , " Oblt . " Ernst Schöller , assuming command in May 1918 . Under Schöller ' s command , " UB - 12 " departed Zeebrugge on 19 August to lay mines in the Downs off the Kentish coast , but never returned . According to one British source , " UB - 12 " was herself mined off Helgoland sometime in August . Author Dwight Messimer considers this unlikely given that Helgoland is nowhere near the route that " UB - 12 " could have taken to get to the Downs . A postwar German study concluded the two most likely fates for " UB - 12 " were that she either struck a British mine or was destroyed by one of her own mines that malfunctioned during deployment . Messimer also considers it possible that " UB - 12 " may have had a diving accident related to her conversion to a minelayer . Some two months after " UB - 12 " s presumed loss , she was credited with the sinking of her final ship . On 27 October , two weeks before the end of the war , the 92 - ton British ship " Calceolaria " struck one of " UB - 12 " s mines near the Elbow Lightvessel and sank . Ships sunk or damaged . < nowiki > * < / nowiki > captured as a prize