Tegetthoff - class battleship The Tegetthoff " - class ( sometimes erroneously named the Viribus Unitis " - class ) was the sole class of dreadnought battleship built for the Austro - Hungarian Navy . Four ships were built , , , and . Three of the four were laid down in Trieste , with " Szent Istvan " being built at Fiume , to incorporate both parts of the dual monarchy into the construction of the ships . The smaller size of the Fiume shipyards meant that " Szent István " was built three years after her sisters , with slightly different characteristics . The first three ships , " Viribus Unitis " , " Tegetthoff " and " Prinz Eugen " were joined by their sister in 1915 , when they bombarded the Italian installations at Ancona . The " Tegetthoff " s attempted to sortie through the Otranto Barrage with the support of lighter ships in 1918 , but failed after " Szent István " was sunk . After the transfer to State of Slovenes , Croats and Serbs , " Virbus Unitus " was sunk by Italian frogmen , and " Tegetthoff " and " Prinz Eugen " were transferred to Italy and France , respectively . Characteristics . Dimensions . The ships had an overall length of , a beam of , and a draught of at deep load . She displaced at load and at deep load . Propulsion . The propulsion consisted of four Parsons steam turbines , each of which was housed in a separate engine - room . The turbines were powered by twelve Babcock & Wilcox boilers . The turbines were designed to produce a total of , which was theoretically enough to attain her designed speed of , but no figures from her speed trials are known to exist . She carried of coal , and an additional of fuel oil that was to be sprayed on the coal to increase its burn rate . At full capacity , she could steam for at a speed of . Armament . Each ship had an armament consisting of twelve / 45 - caliber K 10 guns in four triple turrets mounted on the center - line , forward and aft of the superstructure . Their secondary armament consisted of twelve / 50 K 10 guns mounted in casemate s amidships . Eighteen / 50 K 10 guns were mounted on open pivots on the upper deck above the casemates . Three more 66 - mm K 10 guns were mounted on the upper turrets for anti - aircraft duties . Four submerged torpedo tube s were fitted , one each in the bow , stern and on each broadside ; twelve torpedoes were carried . Armor . The waterline armour belt of the " Tegetthoff " - class measured thick between the midpoints of the fore and aft barbettes and thinned to further towards the bow and stern , but did not reach either the bow or the stern . It was continued to the bow by a small patch of armour . The upper armour belt had a maximum thickness of , but it thinned to from the forward barbette all the way to the bow . The casemate armour was also thick . The sides of the main gun turrets , barbettes and main conning tower were protected by of armour , except for the turret and conning tower roofs which were thick . The thickness of the decks ranged from in two layers . The underwater protection system consisted of the extension of the double bottom up to the lower edge of the waterline armour belt , with a thin plate acting as the outermost bulkhead . It was backed by a torpedo bulkhead that consisted of two layered 25 - millimetre plates . The total thickness of this system was only which made it incapable of containing a torpedo warhead detonation or mine explosion without rupturing . Variations . " Szent István " , built at Fiume , differed from her half - sisters mainly in her machinery . She only had two shafts and two turbines , unlike the four shaft arrangement of the other ships of her class . External differences included a platform built around the fore funnel which extended from the bridge to the after funnel and on which several searchlights were installed . A further distinguishing feature was the modified ventilator trunk in front of the mainmast . She was the only ship of her class not to be fitted with torpedo nets . Construction . The Austro - Hungarian government ordered the construction of a new fleet in 1908 , following the announcement of the start of construction of the first dreadnought for the Regia Marina ( the Italian navy ) , the . The ships of this class were among the first ships to utilize triple gun turrets for their main armament , the first one being the Italian battleship " Dante Alighieri " , which the Austro - Hungarian ships were supposed to act against in a war ; as for the Italian ship , this choice made it possible to deliver a heavier broadside than other dreadnoughts of a similar size . The triple turrets were built at the Škoda Works , in Plzeň , Bohemia ( Czech republic ) , and was available at short notice because Škoda were already working on a design for an order for the Russian navy . The first unit was to bear the name of Wilhelm von Tegetthoff , an Austrian naval admiral of the 19th century , but Franz Joseph I wanted it to be named after his personal motto , " Viribus Unitis " ( Latin for " With united forces " ) . In any event , the class name remained " Tegetthoff " . The first three ships were built at the Stabilimento Tecnico Triestino yard , Trieste , but as a condition of agreeing to the construction and financing of the new fleet , the Hungarian parliament insisted that one of the battleships be built at the Hungarian facility , the Danubius yard at Fiume – Rijeka ( pronounced : riiyeca ) , now Croatia . However , the Danibius shipyard had until then never built anything larger than a destroyer , therefore delayed construction as the yard was extended in preparation for the dreadnought . For this reason the final ship , delivered seventeen months late , was given a Hungarian name — named Szent István after Saint Stephen , the first king and patron saint of Hungary . Service History . World War I . The assistance of the Austro - Hungarian fleet was called upon by the German Mediterranean Division , which consisted of the battlecruiser and light cruiser . The German ships were attempting to break out of Messina , where they had been coaling prior to the outbreak of war — British ships had begun to assemble off Messina in an attempt to trap the Germans . By this time , the Austro - Hungarians had not yet fully mobilized their fleet , though the three " Radetzky " s and three " Tegetthoff " s , along with several cruisers and smaller craft , were available . The Austro - Hungarian high command , wary of instigating war with Great Britain , ordered the fleet to avoid the British ships , and to only openly support the Germans while they were in Austro - Hungarian waters . On 7 August , when the Germans broke out of Messina , the Austro - Hungarian fleet , including the " Tegetthoff " - class battleships , sailed as far south as Brindisi , before returning to port . After the breakout , the Austro - Hungarian navy saw very little action , spending much of its time in its base at Pola ( now Pula , Croatia ) . The navy ' s general inactivity was partly caused by a lack of coal , which became a problem as the war progressed , and partly by a fear of mines in the Adriatic ( which also kept the Italian navy in port for most of the war ) . They did , however , leave Pula to bombard Ancona in May 1915 . On 23 May 1915 , four hours after the Italian declaration of war reached the main Austro - Hungarian naval base at Pola , the members of the " Tegetthoff " class and the rest of the fleet departed to bombard the Italian coast . The Austro - Hungarian ships bombarded the important naval base at Ancona , and later the coast of Montenegro , without opposition ; by the time Italian ships arrived on the scene , the Austro - Hungarians were safely back in Pola . Otranto Raid . In 1918 Admiral Miklós Horthy de Nagybánya became rear admiral of the fleet , and he determined to use the fleet to attack the Otranto Barrage . On 8 June 1918 he took the " Viribus Unitis " and " Prinz Eugen " south with a small supporting flotilla ; on the evening of 9 June , " Szent István " and " Tegetthoff " followed . In trying to make maximum speed in order to catch up , " Szent István " s turbines started to overheat and speed had to be reduced to 12 knots ( 22 km / h ) . When an attempt was made to raise more steam in order to increase to 16 knots ( 30 km / h ) " Szent István " produced an excess of smoke , attracting the attention of a pair of patrolling Italian torpedo boat s at 3 . 20 a . m . on 10 June . " MAS - 21 " attacked " Tegetthoff " , but one of her torpedoes failed to leave the launch tube and the other failed to explode . " MAS - 15 " however succeeded in striking " Szent István " with two torpedoes at 3 : 31 a . m . The " Tegetthoff " returned to the scene to take the " Szent István " in tow . An attempt to beach the ship on nearby Molat Island ( northwest of Zara ) was considered , but the ship was taking on too much water . At 6 : 12 am , with the pumps unequal to the task , " Szent István " capsized , taking 89 of her crew with her . The last half - hour of the sinking was filmed in stages from the " Tegetthoff " ( one of only two battleship sinkings on the high seas to ever be filmed , the other being that of the British battleship in the Second World War ) . Fearing further attacks by torpedo boats or destroyers from the Italian navy , his element of surprise now compromised , Admiral Horthy called off the attack and the fleet returned to base for the remainder of the war . Post - war . After it was clear that Austria - Hungary had lost World War I , the Austrian government decided to give the " Viribus Unitis " , along with much of the Austro - Hungarian fleet , to the newly formed State of Slovenes , Croats and Serbs . This move would have avoided handing the fleet to the Allies , since the new state had declared neutrality . Following the transfer , she was renamed the " Yugoslavia " . Despite the transfer , on 1 November 1918 , two men of the Regia Marina , Raffaele Paolucci and Raffaele Rossetti , rode a primitive manned torpedo ( nicknamed the " Mignatta " or " leech " ) into the Austro - Hungarian naval base at Pola . Using limpet mine s , they then sank the " Viribus Unitis " , as well as the freighter " Wien " . Traveling down the rows of Austrian battleships , the two men encountered the " Viribus Unitis " at around 4 : 40 am . Rossetti placed one canister of TNT on the hull of the battleship , timed to explode at 6 : 30 am . He then flooded the second canister , sinking it on the harbor floor close to the ship . This second canister exploded close to the Austrian freighter " Wien " , resulting in her sinking . The men had no breathing sets , and therefore had to keep their heads above water . They were discovered and taken prisoner just after placing the explosives under the battleship ' s hull . The Italians did not know that the Austrian government had handed over the " Viribus Unitis " , along with most of the Austro - Hungarian fleet , to the newly created State of Slovenes , Croats and Serbs . The two - man team were captured and taken aboard " Viribus Unitis " , where they informed the new captain of the battleship what they had done but did not reveal the exact position of the explosives . Vuković then arranged for the two prisoners to be taken safely to the sister ship , and ordered the evacuation of the ship . The explosion did not happen at 6 : 30 as predicted and Vuković returned to the ship with many sailors ( believing mistakenly that the Italians had lied ) . He therefore remained on his ship and went down with her and 300 – 400 of her crew when the mines exploded shortly afterwards at 6 : 44 . Following the explosion , the battleship sank in 15 minutes . The two Italian crew were interned for a few days until the end of the war and were honored by the Kingdom of Italy with the Gold Medal of Military Valor . On 4 November Italian troops entered Pola and seized " Tegetthoff " and " Prinz Eugen " . The Italians kept " Tegetthoff " for their own use , although they broke her up in 1924 following the Washington Naval Treaty of 1922 , but she had first featured in the movie " Eroi di nostri mari " " ( Heroes of our seas ) " about the sinking of " Szent István " . " Prinz Eugen " became French property — they removed the main armament for inspection and used the ship to test aerial bombardment attacks , before she was finally used as a target ship by the battleships , , and , and sunk in the Atlantic . Bibliography . Other sources