German Type UB I submarine The Type UB I was a class of small coastal submarines ( U - boat s ) built in Germany at the beginning of the First World War . Twenty boats were constructed , most of which went into service with the German Imperial Navy . Boats of this design were also operated by the Austro - Hungarian Navy ( Kaiserliche und Königliche Kriegsmarine " or " K . u . K . Kriegsmarine ) and the Bulgarian Navy . The group is sometimes known as the UB - 1 " class " ' after , the class leader . In the Austro - Hungarian Navy , it was called the ' . Built to meet the need for small maneuverable submarines able to operate in the narrow , shallow seas off Flanders , the vessels were intended to be quickly constructed , then shipped by rail and assembled at their port of operation . The design effort began in mid - August 1914 and by mid - October the first 15 boats were ordered from two German shipyards . The German Imperial Navy subsequently ordered an additional pair of boats to replace two sold to Austria - Hungary , who ordered a further three boats in April 1915 . A total of twenty UB Is were built . Construction of the first boats for Germany began in early November 1914 ; all twenty were completed by October 1915 . Several of the first boats underwent trials in German home waters , but the rest were assembled and tested at either Antwerp or Pola . The German boats operated primarily in the Flanders , Baltic , and Constantinople Flotilla s . The boats were about long and displaced when surfaced and while submerged . All had two bow torpedo tube s and two torpedo es , and were equipped with a deck - mounted machine gun . In 1918 four of the surviving German boats were converted into coastal minelayer s . Of the seventeen boats in German service , two were sold to Austria - Hungary , one was sold to Bulgaria , and nine were lost during the war . One of the five Austro - Hungarian boats was sunk and another mined and not repaired . The five surviving German boats , the four surviving Austro - Hungarian boats , and the Bulgarian boat were all turned over to the Allies after the end of the war and were broken up . Design . In the earliest stages of the First World War the German Army ' s rapid advance along the North Sea coast found the German Imperial Navy without submarines suitable to operate in the narrow and shallow seas off Flanders . By 18 August 1914 , two weeks after the German invasion of Belgium , the planning of a series of small coastal submarines had already begun . The German Imperial Navy stipulated that the submarines must be transportable by rail , which imposed a maximum diameter of . The rushed planning effort — which had been assigned the name " Project 34 " — resulted in the Type UB I design , created specifically for operation from Flanders . The boats were to be about long and to displace about with two bow torpedo tubes . Boats of the Type UB I design were built by two manufacturers , Germaniawerft of Kiel and AG Weser of Bremen , which led to some variations in boats from the two shipyards . The eight Germaniawerft - built boats were slightly longer at length overall , while the twelve Weser - built boats came in shorter than their counterparts . All were abeam and had a draft of . The boats all displaced while surfaced , but differed slightly in displacement submerged . The slightly longer Germaniawerft boats displaced while submerged , as they weighed more than the Weser boats . The drivetrain of the boats consisted of a single propeller shaft driven by a Daimler ( Germaniawerft ) or Körting ( Weser ) diesel engine on the surface , or a Siemens - Schuckert electric motor for underwater travel . The Weser boats were capable of nearly on the surface and a little more than submerged . The Germaniawerft boats were about slower than their Bremen - made counterparts . The boats were equipped with two bow torpedo tubes and carried two torpedoes . They were also armed with a single machine gun affixed to the deck . Construction . The German Imperial Navy ordered its first fifteen Type UB I boats on 15 October 1914 . Eight boats — numbered " UB - 1 " to " UB - 8 " — were ordered from Germaniawerft of Kiel , and seven boats — numbered " UB - 9 " to " U - 15 " — from AG Weser of Bremen . After two of the class , " UB - 1 " and " UB - 15 " , were sold in February 1915 to ally Austria - Hungary ( becoming " U - 10 " and " U - 11 " in the Austro - Hungarian Navy ) , the German Imperial Navy ordered " UB - 16 " and " UB - 17 " from Weser . A further three for Austria - Hungary — " U - 15 " , " U - 16 " , and " U - 17 " — had been ordered from Weser by April , bringing the total number constructed to twenty . " UB - 1 " and " UB - 2 " were laid down on 1 November 1914 at the Germaniawerft yard at Kiel . " UB - 1 " was launched on 22 January 1915 , just 75 working days later . " UB - 2 " s launch followed on 13 February . Among the Weser boats , " UB - 9 " was laid down first , on 6 November 1914 , and launched on 6 February 1915 , a week ahead of " UB - 2 " . These first three boats launched underwent trials in home waters , but most of the other members of the class were shipped via rail and underwent trials at their assembly point . The process of shipping the submarines by rail involved breaking the submarines 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 . Type UB I boats destined for service with the Flanders Flotilla made a five - day journey to Antwerp for the two - to three - week assembly process . After assembly at Antwerp the boats were towed by barge to Bruges for trials . Boats selected for service in the Mediterranean were sent to the Austro - Hungarian port of Pola for assembly . The total time from departure of the railcars from the shipyard to operational readiness for the boats was about six weeks . By July 1915 all seventeen of the German Imperial Navy Type UB Is had been completed . Service . During their trials the Type UB Is were found to be too small and too slow and had a reputation for being underpowered ; one commander compared his Type UB I to a " sewing machine " . According to authors R . H . Gibson and Maurice Prendergast in their 1931 book " The German Submarine War , 1914 – 1918 " , the UBs did not have enough power to chase down steamers while surfaced and lacked the endurance to spend any extended amount of time underwater , exhausting their batteries after little over an hour ' s running . In - service use revealed another problem : with a single propeller shaft / engine combination , if either component failed , the U - boat was almost totally disabled . Another reported problem with the Type UB Is was the tendency to break trim after the firing of torpedoes . The boats were equipped with compensating tanks designed to flood and offset the loss of the C / 06 torpedo ' s weight , but this system did not always function properly ; as a result , when firing from periscope depth the boat could broach after firing or , if too much weight was taken on , plunge to the depths . When " UB - 15 " torpedoed and sank in June 1915 , the tank failed to properly compensate , forcing the entire crew to run to the stern to offset the trim imbalance . Despite the problems , the " tin tadpoles " , as the Germans referred to them , were in active service from March 1915 through the end of the war , with half of the twenty boats lost during the war . Boats of the class served in three navies : the German Imperial Navy , the Austro - Hungarian Navy , and the Bulgarian Navy . In German service , they served primarily in the Flanders Flotilla , the Baltic Flotilla , and the Constantinople Flotilla . German Imperial Navy . Flanders Flotilla . The first Type UB I to enter service was " UB - 10 " , which formed the nucleus of the Flanders Flotilla , on 27 March 1915 . By the end of April five more Type UB I boats had become operational . " UB - 10 " was eventually joined in the Flanders Flotilla by " UB - 2 " , " UB - 4 " , " UB - 5 " , " UB - 6 " , " UB - 12 " , " UB - 13 " , " UB - 16 " , and " UB - 17 " ; of these , only " UB - 2 " made the journey to Flanders by sea rather than rail . " UB - 4 " departed on the first patrol from Flanders on 9 April , and was responsible for sinking the first ship sent down by the flotilla . The Type UB I boats of the Flanders Flotilla originally patrolled the area between the United Kingdom and the Netherlands , but began patrolling the English Channel after " UB - 6 " pioneered a route past British antisubmarine nets and mines in the Straits of Dover in late June . Over the Type UB Is ' first year of service , " UB - 4 " and " UB - 13 " were both lost , and " UB - 2 " and " UB - 5 " were transferred to the Baltic Flotilla . In March 1917 , " UB - 6 " ran aground in Dutch waters and was interned for the rest of the war , along with her crew . The four remaining Type UB Is in Flanders — " UB - 10 " , " UB - 12 " , " UB - 16 " , " UB - 17 " — were all converted to minelayers by 1918 , having their torpedo tubes removed and replaced with chutes to carry up to eight mines . All but " UB - 10 " were lost in 1918 ; " UB - 10 " , in poor repair and out of service , was scuttle d in October 1918 when the Germans evacuated from Flanders . Baltic Flotilla . " UB - 9 " was initially assigned to the Baltic Flotilla , and was joined by " UB - 2 " and " UB - 5 " in early 1916 . All three became training boats at Kiel in 1916 , joining " UB - 11 " in that duty . Little information is available about the Type UB I boats operating in the Baltic . Constantinople Flotilla . Four of the German Imperial Navy boats — " UB - 3 " , " UB - 7 " , " UB - 8 " , and " UB - 14 " — were selected for service with the Constantinople Flotilla . All were sent to Pola for assembly and trials there as part of the Pola Flotilla before sailing on to join the Constantinople Flotilla . " UB - 3 " disappeared en route to Constantinople in May 1915 , but the other three arrived there by mid - June . The three Type UB I boats of the Constantinople Flotilla seem to have patrolled primarily in the Black Sea . " UB - 8 " was transferred to the Bulgarian Navy in May 1916 , and " UB - 7 " disappeared in the Black Sea in October 1916 , leaving " UB - 14 " as the sole remaining German Type UB I in the flotilla ; she was surrendered at Sevastopol in November 1918 to French armies stationed there during the Russian Civil War . Austro - Hungarian Navy . " UB - 1 " and the still incomplete " UB - 15 " were sold to the Austria - Hungary in February 1915 ; both were dismantled and shipped to Pola in May . After one cruise under the German flag , each boat was commissioned into the Austro - Hungarian Navy . The pair — renamed " U - 10 " and " U - 11 " , respectively — were joined by " U - 15 " , " U - 16 " , and " U - 17 " in October . Known as the " U - 10 " or the " Okarina " ( ) class as a part of the Austro - Hungarian Navy , the five boats operated primarily in the Adriatic in patrols off Italy and Albania . " U - 10 " ( ex " UB - 1 " ) hit a mine in July 1918 and was beached , but had not been repaired by the end of the war . " U - 16 " was sunk after she torpedoed an Italian destroyer in October 1916 , and the remaining three ( and the unrepaired " U - 10 " ) were ceded to Italy at the end of the war . Bulgarian Navy . After " UB - 8 " was transferred to the Bulgarian Navy in May 1916 , she was renamed " Podvodnik No . 18 " ( in Cyrillic : " Пoдвoдник No . 18 " ) . She was Bulgaria ' s first submarine , and was engaged primarily in coastal defense duties off Bulgaria ' s main Black Sea port of Varna . " Podvodnik No . 18 " survived the war and was ceded to France after the Treaty of Neuilly - sur - Seine . List of Type UB I submarines . Twenty Type UB I submarines were built , 17 for the German Imperial Navy and three for the Austro - Hungarian Navy . Two of the German submarines — " UB - 1 " and " UB - 15 " — were sold to Austria - Hungary and commissioned into the Austro - Hungarian Navy as " U - 10 " and " U - 11 " , respectively . Those two and a further three built by AG Weser comprised the virtually identical " U - 10 " class for the Austro - Hungarian Navy . Another of the German submarines , " UB - 8 " , was sold to Bulgaria in May 1916 , becoming " Podvodnik No . 18 " . Austro - Hungarian Navy . In the Austro - Hungarian Navy the Type UB I boats were known as the " U - 10 " class , which consisted of two former German Type UB I boats and three built specifically for Austria - Hungary . In addition , four of the German Type UB Is assigned to the Pola Flotilla based at the Austro - Hungarian Navy ' s main naval base at Pola were assigned Austro - Hungarian designations . These four boats remained under commission in the German Imperial Navy , retained German crews and commanders , and received orders from the German flotilla commander at Pola . Bulgarian Navy . Germany and Bulgaria negotiated the purchase of two UB I boats for the Bulgarian Navy , and , in 1916 . Two crews of Bulgarian sailors were sent to Kiel for training . Before the purchase could be completed , " UB - 7 " was sunk , leaving only one boat for Bulgaria . On 25 May 1916 , " UB - 8 " was officially transferred to Bulgaria for the remainder of the war . Key