SM U-4 (Austria-Hungary)

At the beginning of World War I, she was one of only four operational submarines in the Austro-Hungarian Navy.[10] On 27 September 1914, U-4 began operating reconnaissance cruises out of the naval base at Cattaro under the command of Linienschiffsleutnant Hermann Jüstel.[5][9] U-4 attacked the cruiser Waldeck-Rousseau on 17 October, but the French vessel escaped without serious damage.[11] In late November, U-4 seized the 13 GRT Albanian sailing vessel Fiore del Mar as a prize off Montenegro.[12] U-4 received her first radio set the following month.[9]

U-4's next success was the capture of three Montenegrin boats on 19 February 1915.[9] Rudolf Singule, who was to become U-4's most successful commander,[13] assumed command of the boat in April 1915.[5][Note 3] Around the same time, the boat was equipped with a 3.7-centimeter (1.5 in) quick firing (QF) deck gun.[9] On 24 May, in the Gulf of Drin, U-4 unsuccessfully attacked an Italian Lombardia-class cruiser,[9] but on 9 June, Singule spotted the British cruiser Dublin 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.[14] Twelve men on Dublin died in the attack,[15] but the cruiser made her way safely, albeit damaged, back to port.[14]

On 18 July, U-4 chanced upon an Italian squadron of ships shelling the railroads at Dubrovnik. Singule selected the Italian armored cruiser Giuseppe Garibaldi as a target and torpedoed her.[16][17] Giuseppe Garibaldi—at 7,234 tons, the largest ship sunk by U-4[13]—sank with a loss of 53 men; 525 men survived.[9] Conway's All the World's Fighting Ships 1906–1921 calls the sinking of Giuseppe Garibaldi as U-4's greatest success.[2] In August, she was sent out to search for her missing sister ship, U-3,[9] which was overdue, having been sunk on 13 August by the French destroyer Bisson.[4] In November, U-4 made an unsuccessful attack on a British Topaze-class cruiser.[9] In early December, U-4 dispatched two small Albanian vessels in the Gulf of Drin.[9][18] The 10 GRT sailing vessel Papagallo was sunk,[19] and the Gjovadje was taken as a prize.[18] 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.[20]

In early February, U-4 sank the 475 GRT French patrol vessel Jean Bart 6 nautical miles (11 km) southwest of Cape Laghi, off Durazzo.[21][Note 4] Just five days later, U-4 made an unsuccessful attack on a British Birmingham-class cruiser.[9] Over 26 and 27 March, U-4 participated in a search for the lost Austro-Hungarian submarine U-24.[9][Note 5] Three days later, U-4 sank the British schooner John Pritchard Of Carnar with explosive charges off the island of Antipaxos.[22] In July, U-4 was outfitted with a new 66 mm (2.6 in) deck gun,[23] which equaled the main gun planned for the U-20 class, under construction at the time.[24]

On 2 August, U-4 missed an Italian Nino Bixio-class cruiser 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.[23][Note 6] Some two months later, U-4 sank the Italian tanker Margaretha at position 40°1′N 17°44′E. Margaretha, originally the J.M.Lennard & Sons ship Atilla, went down without any reported loss of life on 13 October.[25][26]

In early May 1917, U-4 sank the steamer Perseo—the second largest ship sunk by the boat[13]—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.[27] 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 Helgoland, Saida, and Novara attacked the drifters that deployed the anti-submarine nets that formed part of the Barrage, sinking 14, damaging 5, and taking 72 prisoners.[28][Note 7] Destroyers Csepel and Balaton 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 U-27 (assigned to patrol between Brindisi and Cattaro) and the German UC-25 (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.[28]

On 30 May at Corfu, U-4 torpedoed and sank the French passenger steamer SS Italia, in operation by the French Navy as an armed boarding ship.[29] 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.[23][30] 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.[23]

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.[23] U-4 was the longest serving Austro-Hungarian submarine,[2] and sank a total of 14,928 GRT and 7,345 tons enemy shipping during the war.[5]