SM UB - 8 SM " UB - 8 was a German Type UB I submarine or U - boat in the German Imperial Navy ( ) during World War I . She was sold to Bulgaria in 1916 and renamed Podvodnik No . 18 " ( ) , and was the first ever Bulgarian submarine . " UB - 8 " was ordered in October 1914 and was laid down at the AG Weser shipyard in Bremen in November . " UB - 8 " 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 - 8 " was originally one of a pair of UB I boats sent to the Austro - Hungarian Navy to replace an Austrian pair to be sent to the Dardanelles , and was broken into sections and shipped by rail to Pola in March 1915 for reassembly . She was launched and commissioned as SM " UB - 8 " in the German Imperial Navy in April when the Austrians opted out of the agreement . Although briefly a part of the Pola Flotilla at commissioning , " UB - 8 " spent the majority of her German career patrolling the Black Sea as part of the Constantinople Flotilla . The U - boat sank two ships . One of them , , was disguised by the British Admiralty as a Royal Navy battlecruiser as part of a decoy operation . In October , she helped repel a Russian bombardment of Bulgaria . In May 1916 , the submarine was transferred to the Bulgarian Navy as " Podvodnik No . 18 " and commissioned in a ceremony that was attended by Crown Prince Boris and Prince Kiril . In Bulgarian service , the submarine patrolled the Bulgarian Black Sea coast and had encounters with Russian vessels on several occasions . After the war ended , the submarine was surrendered to France in February 1919 and scrapped at Bizerta in August 1921 . However in July 2011 Viceadmiral Manushev , Commander of the Bulgarian Navy , announced that the submarine , discovered in 2010 at the sea bottom near the town of Varna , is UB - 8 . Divers discovered manufacturer numbers and according to them the identity is confirmed . 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 - 8 " was last boat of the initial allotment of eight submarines — numbered from — ordered on 15 October from Germaniawerft of Kiel , just shy of two months after planning for the class began . " UB - 8 " was laid down by Germaniawerft in Kiel on 4 December . As built , " UB - 8 " was long , abeam , and had a draft of . She had a single Daimler 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 - 8 " was rated to a diving depth of , and could completely submerge in 33 seconds . " UB - 8 " was armed with two torpedo es in two bow torpedo tube s . She was also outfitted for a single machine gun on deck . " UB - 8 " s standard complement consisted of one officer and thirteen enlisted men . While " UB - 8 " s construction neared completion in early March 1915 , Enver Pasha and other Turkish leaders were pleading with their German and Austro - Hungarian allies to send submarines to the Dardanelles to help attack the British and French fleet pounding Turkish positions . The Germans induced the Austro - Hungarian Navy ( ) to send two boats — its own Germaniawerft - built boats and — with the promise of and " UB - 8 " as replacements . When work on " UB - 7 " and " UB - 8 " was complete at the Germaniwerft yard , they were both 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 . The boats were ready for shipment to the main Austrian naval base at Pola on 15 March , despite the fact that the Austrian pair was still not ready . German engineers and technicians that accompanied the German boats to Pola worked under the supervision of " Kapitänleutnant " Hans Adam , head of the newly created U - boat special command ( ) . Typically , the UB I assembly process took about two to three weeks , and , accordingly , " UB - 8 " was launched at Pola sometime in April . German career . During her trials , " UB - 8 " was assigned the Austrian number of " U - 8 " and an Austrian commander . Her German crew at Pola — since it was still the intent for " UB - 8 " to be transferred to the " K . u . K . Kriegsmarine " — wore either civilian clothes or Austrian uniforms . As time dragged on , the Austrian " U - 3 " and " U - 4 " were still not ready , and eventually Admiral Anton Haus , the head of the Austro - Hungarian Navy , reneged on his commitment because of the overt hostility from neighbor and former ally Italy . With the change of heart from the Austrians , Germany resolved to retain " UB - 8 " and send her to the aid of the Turks . So , the boat was commissioned into the German Imperial Navy as SM " UB - 8 " on 23 April under the command of " Kapitänleutnant " Ernst von Voigt , a 27 - year - old first - time U - boat commander . At commissioning , the boat temporarily joined the Pola Flotilla ( ) . Because of her limited range , " UB - 8 " would not have been able to make the entire journey to Turkey , so on 2 May , she was towed by the Austrian cruiser from Pola down the Adriatic and through the Straits of Otranto . The duo continued until spotted by French forces near Kefalonia . " UB - 8 " slipped the tow and " Novara " raced back into the Adriatic without incident . Two days after her departure , " UB - 8 " was running on the surface when the stern of the boat suddenly dropped . The watch officer , on the conning tower with the helmsman and a lookout , was able to partially close the hatch before the entire submarine slipped below the waves , depositing the three men in the water . On board the submarine , water continued to pour in through the hatch and the boat was sinking by the stern . Voigt ordered the interior hatch to the control room sealed and all the ballast tanks filled with compressed air to increase buoyancy . The tactic returned " UB - 8 " to the surface where the boat ' s diesel engines were restarted . Voigt circled back for the missing crewmen but only the watch officer and helmsman were recovered ; the lookout had drowned . On 29 May 1915 , " UB - 8 " came upon an Allied convoy near Lemnos , and , enticed by the prospect of hitting what he identified as the Royal Navy battlecruiser , Voigt allowed five fully laden transport ships to pass unmolested . When he had a clear shot , Voigt launched one of his torpedoes at the stationary ship and hit it , sending debris into the air . Unfortunately for Voigt and " UB - 8 " , they had in fact torpedoed the British ocean liner , which was a participant in an Admiralty plan to disguise large liners as Royal Navy capital ships . " Merion " , which eventually sank on 31 May , had been outfitted with wood and canvas " guns " and overloaded with cement and stones to approximate the profile of " Tiger " . There are no reports of any deaths during " Merion " s sinking . On 4 June , " UB - 8 " became the first submarine in the new Constantinople Flotilla ( ) based in Constantinople ( present - day Istanbul ) . Despite German intentions to use her in the Dardanelles , " UB - 8 " was ineffective because she was hampered by her limited torpedo supply and her weak engines , which made negotiating the strong currents there nearly impossible . Because of this , " UB - 8 " was sent to patrol in the Black Sea , where she was active by late July . Off Sevastopol on 31 July , " UB - 8 " sank her second and final ship , the 1 , 265 - ton Russian ship " Peter Melnikoff " . On 12 August , " UB - 8 " fired a torpedoe at HMS Manica from 500 yards , which passed under Manica ' s shallow draught , the submarine was then sighted outside net , two torpedoes fired and missed Manica , which hit the net at an acute angle and burst . An attack two days later on similar vessels was also unsuccessful . In September , " UB - 7 " and " UB - 8 " were sent to Varna , Bulgaria , and from there , to patrol off the Russian Black Sea coast . Because Bulgaria had joined the Central Powers , battleships of the Russian Black Sea Fleet , and aircraft from the seaplane carrier s and began attacks on Varna and the Bulgarian coast on 25 October . " UB - 7 " and " UB - 8 " , both based out of Varna by this time , sortied to disrupt the bombardment . " UB - 8 " was never able to launch any attacks , but " UB - 7 " launched a torpedo at the ( most well - known under her former name of " Potemkin " ) , but it missed . Despite the lack of any success by either submarine , their presence did cause the Russians to break off their attacks and withdraw . In early 1916 , " UB - 7 " and " UB - 8 " were still cruising in the Black Sea out of Varna . The Germans did not have good luck in the Black Sea , which was not a priority for them . The Bulgarians , who saw the value of the submarines in repelling Russian attacks , began negotiations to purchase " UB - 7 " and " UB - 8 " . Bulgarian sailors practiced in the pair of boats and technicians were sent to Kiel for training at the German submarine school there . The transfer of " UB - 8 " to the Bulgarian Navy took place on 25 May 1916 , but for reasons unreported in sources , " UB - 7 " remained under the German flag . Bulgarian career . Upon acceptance of " UB - 8 " by the Bulgarian Navy , she was renamed " Podvodnik No . 18 " ( in Cyrillic : " Пoдвoдник №18 " ) . Although the commissioning ceremony for " Podvodnik No . 18 " was kept out of newspapers , it was attended by Crown Prince Boris and his brother Prince Kiril , who both boarded the submarine for a ceremonial first voyage to Euxinograd , the Bulgarian summer palace located just north of Varna . In Bulgarian service , the submarine was armed with a deck gun that supplemented its machine gun . " Podvodnik No . 18 " s first patrol under the Bulgarian flag took place on 4 and 5 July 1916 when she sailed to Cape Shabla and Mangalia . The submarine was used for reconnaissance and coastal defense , and patrolled a regular route . This route was a loop that began in Varna and went northward to Kaliakra , Mangalia , and Constanţa ; then southward to Burgas , and Sozopol ; then ended at Varna . On 6 September , she had an encounter with the Russian destroyers and , drove off Russian submarines on other occasions , and on 16 December helped turn back a Russian sortie against Balchik . After the Russian withdrawal from World War I in 1917 , " Podvodnik No . 18 " s activities were greatly reduced . After the end of the war , " Podvodnik No . 18 " was surrendered to the French on 23 February 1919 . Towed to Bizerta , she was scrapped after August 1921 .