SM U - 4 ( Austria - Hungary ) SM " U - 4 or U - IV " was a " U - 3 " - class submarine or U - boat built for and operated by the Austro - Hungarian Navy ( ) before and during the First World War . The submarine was built as part of a plan to evaluate foreign submarine designs , and was the second of two boats of the class built by Germaniawerft of Kiel , Germany . " U - 4 " was authorized in 1906 , begun in March 1907 , launched in November 1908 , and towed from Kiel to Pola in April 1909 . The double - hull ed submarine was just under long and displaced between , depending on whether surfaced or submerged . The design of the submarine had poor diving qualities and several modifications to " U - 4 " s diving plane s and fins occurred in her first years in the Austro - Hungarian Navy . Her armament , as built , consisted of two bow torpedo tubes with a supply of three torpedoes , but was supplemented with a deck gun , the first of which was added in 1915 . The boat was commissioned into the Austro - Hungarian Navy in August 1909 , and served as a training boat — sometimes making as many as ten cruises a month — through the beginning of the First World War in 1914 . At the start of that conflict , she was one of only four operational submarines in the Austro - Hungarian Navy U - boat fleet . Over the first year of the war , " U - 4 " made several unsuccessful attacks on warships and captured several smaller vessels as prizes . In July 1915 , she scored what " Conway ' s All the World ' s Fighting Ships , 1906 – 1921 " calls her greatest success when she torpedoed and sank the Italian armored cruiser , the largest ship hit by " U - 4 " during the war . In mid - May 1917 , " U - 4 " was a participant in a raid on the Otranto Barrage which precipitated the Battle of Otranto Straits . In a separate action that same month , " U - 4 " sank her second largest ship , the Italian troopship " Perseo " . She scored her final success in July 1917 with the sinking of a French tug . In total , " U - 4 " sank twelve ships totaling over . She survived the war as Austria - Hungary ' s longest serving submarine , was ceded to France as a war reparation , and scrapped in 1920 . Design and construction . " U - 4 " was built as part of a plan by the Austro - Hungarian Navy to competitively evaluate foreign submarine designs from Simon Lake , Germaniawerft , and John Philip Holland . The Austro - Hungarian Navy authorized the construction of " U - 4 " ( and sister ship , " U - 3 " ) in 1906 by Germaniawerft of Kiel , Germany . " U - 4 " was laid down on 12 March 1907 and launched on 20 November 1908 . After completion , she was towed via Gibraltar to Pola , where she arrived on 19 April 1909 . " U - 4 " s design was an improved version of Germaniawerft ' s design for the Imperial German Navy ' s first U - boat , , and featured a double hull with internal saddle tank s . The Germaniawerft engineers refined the design ' s hull shape through extensive model trials . " U - 4 " was long by abeam and had a draft of . She displaced surfaced and submerged . She was armed with two bow torpedo tubes , and was designed to carry up to three torpedoes . Early career . After " U - 4 " s arrival at Pola in April 1909 , she was commissioned into the Austro - Hungarian Navy on 29 August 1909 as SM " U - 4 " . During the evaluation of the " U - 3 " class conducted by the Navy , the class ' poor diving and handling characteristics were noted . To alleviate the diving problems , " U - 4 " s fins were changed in size and shape several times , and eventually , the front diving plane s were removed and a stationary stern flap was affixed to the hull . " U - 4 " served as a training boat between 1910 and 1914 and made as many as ten cruises per month in that capacity . World War I . 1914 – 1916 . At the beginning of World War I , she was one of only four operational submarines in the Austro - Hungarian Navy . On 27 September 1914 , " U - 4 " began operating reconnaissance cruises out of the naval base at Cattaro under the command of " Linienschiffsleutnant " Hermann Jüstel . " U - 4 " attacked the cruiser " Waldeck - Rousseau " on 17 October , but the French vessel escaped without serious damage . In late November , " U - 4 " seized the Albanian sailing vessel " Fiore del Mar " as a prize off Montenegro . " U - 4 " received her first radio set the following month . " U - 4 " s next success was the capture of three Montenegrin boats on 19 February 1915 . Rudolph Singule , who was to become " U - 4 " s most successful commander , assumed command of the boat in April 1915 . Around the same time , the boat was equipped with a quick firing ( QF ) deck gun . On 24 May , in the Gulf of Drin , " U - 4 " unsuccessfully attacked an Italian , but on 9 June , Singule spotted the British cruiser escorting a convoy along the Montenegrin coast . Despite a screen of six destroyers , " U - 4 " was able to torpedo " Dublin " off San Giovanni de Medua . Twelve men on " Dublin " died in the attack , but the cruiser made her way safely , albeit damaged , back to port . On 18 July , " U - 4 " chanced upon an Italian squadron of ships shelling the railroads at Dubrovnik . Singule selected the Italian armored cruiser as a target and torpedoed her . " Giuseppe Garibaldi " — at , the largest ship sunk by " U - 4 " — sank with a loss of 53 men ; 525 men survived . " Conway ' s All the World ' s Fighting Ships , 1906 – 1921 " calls the sinking of " Giuseppe Garibaldi " as " U - 4 " s greatest success . In August , she was sent out to search for her missing sister ship , , which was overdue , having been sunk on 13 August by the French destroyer " Bisson " . In November , " U - 4 " made an unsuccessful attack on a British . In early December , " U - 4 " dispatched two small Albanian vessels in the Gulf of Drin . The sailing vessel " Papagallo " was sunk , and the " Gjovadje " was taken as a prize . New periscopes and a new gyrocompass were installed on " U - 4 " later in the month . On 3 January 1916 , operating again near the Gulf of Drin , Singule and " U - 4 " seized another Albanian sailing vessel , " Halil " , and sank two smaller boats . In early February , " U - 4 " sank the French patrol vessel " Jean Bart " southwest of Cape Laghi , off Durazzo . Just five days later , " U - 4 " made an unsuccessful attack on a British . Over 26 and 27 March , " U - 4 " participated in a search for the lost Austro - Hungarian submarine . Three days later , " U - 4 " sank the British schooner " John Pritchard Of Carnar " with explosive charges off the island of Antipaxos . In July , " U - 4 " was outfitted with a new 66 mm / 26 ( 2 . 6 in ) deck gun , which equaled the main gun planned for the , under construction at the time . On 2 August , " U - 4 " missed an Italian in a torpedo attack , and three days later , was missed by two torpedoes in an attack by an enemy submarine . A week later , " U - 4 " successfully torpedoed and sank the Italian schooner " Ponte Maria " off Brindisi and weathered another unsuccessful enemy submarine attack . Two days later , on 14 August , " U - 4 " closed out her busy month of August by attacking the British steamer " Inverbervie " off Cape Nau . Some two months later , " U - 4 " sank the Italian tanker " Margaretha " at position . " Margaretha " , originally the J . M . Lennard & Sons ship " Atilla " , went down without any reported loss of life on 13 October . 1917 – 1918 . In early May 1917 , " U - 4 " sank the steamer " Perseo " — the second largest ship sunk by the boat — in the Ionian Sea . Although " Perseo " was serving as an Italian troop transport at the time , there are no reports of casualties in the 4 May attack . In mid - May 1917 , " U - 4 " participated in a support role in a raid on the Otranto Barrage that precipitated the Battle of Otranto Straits . On the night of 14 / 15 May , the Austro - Hungarian cruisers , , and attacked the drifters that deployed the anti - submarine net s that formed part of the Barrage , sinking 14 , damaging 5 , and taking 72 prisoners . Destroyers and were sent to simultaneously attack Italian transports shuttling between Italy and Valona , and sank an Italian destroyer and a munitions ship . " U - 4 " , which was posted near Valona , was a part of a force of three U - boats intended to intercept British and Italian ships responding to the attacks ; the other two were the Austro - Hungarian ( assigned to patrol between Brindisi and Cattaro ) and the German ( assigned to mine Brindisi ) . A squadron of British cruisers and Italian and French destroyers joined the battle against the Austro - Hungarian cruisers on 15 May . Several ships on each side were damaged by the time the engagement was broken off . As a result of the attacks the drifter line of the Barrage was moved farther south and maintained only during the day , a success for the Central Powers . " U - 4 " did not take any offensive action during the raid and ensuing battle . On 30 May at Corfu , " U - 4 " torpedoed and sank the French passenger steamer " Italia " , in operation by the French Navy as an armed boarding ship . On 19 June , " U - 4 " scored a triple victory when she sank the French steamers " Edouarde Corbière " and " Cefira " and the Greek ship " Kerkyra " off Taranto . " U - 4 " sank what would be her final ship on 12 July , when she torpedoed the French tug " Berthilde " off Cape Stilo . In September , " U - 4 " received a new bulwark on her conning tower . " U - 4 " arrived at Pola for the final time on 1 November 1918 and was there at the war ' s end . She was ceded to France as a war reparation and scrapped in 1920 . " U - 4 " was the longest serving Austro - Hungarian submarine , and sank a total of enemy shipping during the war .