Yugoslav torpedo boat T4

The original concept of operation for the 250t-class boats was that they would sail in a flotilla at the rear of a cruising battle formation, and were to intervene in fighting only if the battleships around which the formation was established were disabled, or in order to attack damaged enemy battleships.[9] When a torpedo attack was ordered, it was to be led by a scout cruiser, supported by two destroyers to repel any enemy torpedo boats. A group of four to six torpedo boats would deliver the attack under the direction of the flotilla commander.[10] During World War I, 79 T was used for convoy, patrol, escort and minesweeping tasks, anti-submarine operations,[1] and shore bombardment missions.[11]

Italy declared war on Austria-Hungary on 23 May 1915,[12] and hostilities in the Adriatic, which had thus far mostly involved intermittent forays by the French fleet,[13] immediately intensified.[12] Almost the entire Austro-Hungarian fleet left its main fleet base at Pola – in the upper Adriatic – soon after the declaration to deliver an immediate response against Italian cities and towns along the Adriatic coast, aiming to interdict land and sea transport between southern Italy and the northern regions of that country which were expected to be a theatre of land operations. The fleet split into six groups with a range of targets up and down the coast.[12] On 24 May, 79 T and seven other 250t-class boats participated in this operation, known as the Bombardment of Ancona, which involved shelling of various Italian shore-based targets, with 79 T involved in the shelling of Porto Corsini near Ravenna.[14] During that action, an Italian 120 mm (4.7 in) shore battery returned fire, hitting the light cruiser Novara and damaging one of the other 250t-class boats.[15] On 27 July, a group led by Novara and the scout cruiser Admiral Spaun, with two destroyers, 79 T and two other 250t-class boats shelled the railway line between Ancona and Pesaro during a seaplane raid on Ancona.[16] On 17 August, the 1st Torpedo Flotilla shelled the island chain of Pelagosa in the middle of the Adriatic, and 79 T was part of a force tasked to protect the southern approaches to the islands from enemy submarines. The success of this bombardment, which destroyed the only source of drinking water, caused the Italians to abandon Pelagosa.[17]

In late November 1915, the Austro-Hungarian fleet deployed a force from Pola to Cattaro in the southern Adriatic; this force included six of the eight T-group torpedo boats. This force was tasked to maintain a permanent patrol of the Albanian coastline and interdict any troop transports crossing from Italy.[18] On 9 December, 79 T, three destroyers, two Kaiman-class torpedo boats and two other 250t-class boats formed a group led by the protected cruiser Szigetvár which escorted seaplanes during a raid on Ancona.[19] On the night of 31 May/1 June 1916, the Tátra-class destroyers Orjen and Balaton, accompanied by 79 T and two other 250t-class boats, raided the Otranto Barrage, an Allied naval blockade of the Strait of Otranto. Orjen sank one drifter, but once the alarm had been raised, the Austro-Hungarian force withdrew.[20]

In 1917, one of 79 T's 66 mm guns was placed on an anti-aircraft mount,[2] and on 21 May of that year, the suffix of all Austro-Hungarian torpedo boats was removed, and thereafter they were referred to only by their numeral.[1] On 28 November, a number of 250t-class boats were involved in two shore bombardment missions. In the first mission, 79 and two other 250t-class boats supported the bombardment of Senigallia by three destroyers, before they were joined by five more 250t-class boats and another three destroyers for the bombardment of Porto Corsini, Marotta and Cesenatico.[21] The bombardment damaged the railway tracks between Senigallia and Rimini and destroyed one locomotive and several wagons, but when the flotilla moved to attack two small steamers, an Italian armoured train arrived and engaged them with its 15 cm (6 in) guns, and they broke off. On the return voyage to Pola, the ships were apparently pursued by Italian warships, but Admiral Spaun sailed to provide support, and the Italians withdrew.[22] On 1 February 1918, a mutiny broke out among the sailors of some vessels of the Austro-Hungarian Navy at the Đenovići anchorage within the Bocche, largely over poor food, lack of replacement uniforms and supplies, and insufficient leave, although the poor state of the Austro-Hungarian economy and its impact on their families was also a factor. 79 was moored in the Castelnuovo anchorage and her crew did not participate in the revolt, possibly because on smaller vessels the officers and sailors endured similar conditions, and their vessels were constantly in action, unlike the crews of the larger ships. Loyal ships were despatched to the Bocche from Pola, but by the time they arrived on 3 February, the mutiny had ended.[23]

By 1918, the Allies had strengthened their ongoing blockade on the Strait of Otranto, as foreseen by the Austro-Hungarian Navy. As a result, it was becoming more difficult for the German and Austro-Hungarian U-boats to get through the strait and into the Mediterranean Sea. In response to these blockades, the new commander of the Austro-Hungarian Navy, Konteradmiral Miklós Horthy, decided to launch an attack on the Allied defenders with battleships, scout cruisers, and destroyers.[24] During the night of 8/9 June 1918, Horthy left the naval base of Pola in the upper Adriatic with the dreadnought battleships Viribus Unitis and Prinz Eugen. At about 23:00 on 9 June, after some difficulties getting the harbour defence barrage opened, the dreadnoughts Szent István and Tegetthoff,[25] escorted by one destroyer and six torpedo boats, including 79, also departed Pola and set course for Slano, north of Ragusa, to rendezvous with Horthy in preparation for a coordinated attack on the Otranto Barrage. About 03:15 on 10 June,[lower-alpha 2] while returning from an uneventful patrol off the Dalmatian coast, two Italian MAS boats, MAS 15 and MAS 21, spotted the smoke from the Austro-Hungarian ships.[27] With their engines off, the two Italian boats waited for the lead ships of the starboard escort to pass, before launching their attack.[28] Both boats successfully penetrated the escort screen and split to engage the dreadnoughts individually. MAS 21 attacked Tegetthoff, but her torpedoes missed.[27] Under the command of Luigi Rizzo, MAS 15 fired two torpedoes at 03:25, both of which hit Szent István. Both boats evaded pursuit. The torpedo hits on Szent István were abreast of her boiler rooms, which flooded, knocking out power to the pumps. Szent István capsized less than three hours after being torpedoed.[26] This disaster essentially ended Austro-Hungarian fleet operations in the Adriatic for the remaining months of the war.[29]

79's final action of the war was on 26 September, when three Austro-Hungarian steamers were attacked by the British submarine H1 near Cape Menders (current day Cape Mandra near Ulcinj, Montenegro). The two escorting destroyers repelled the attack, assisted by 79, three other 250t-class boats, and a seaplane.[30]

The Austro-Hungarian Empire sued for peace in November 1918, and 79 survived the war intact.[1] In 1920, under the terms of the previous year's Treaty of Saint-Germain-en-Laye by which rump Austria officially ended World War I, she was allocated to the Kingdom of Serbs, Croats and Slovenes (KSCS, later Yugoslavia).[31] Immediately after the Austro-Hungarian capitulation, French troops occupied Cattaro, which was treated by the Allies as Austro-Hungarian territory.[32] During the French occupation, the captured Austro-Hungarian Navy ships moored at Cattaro were neglected, and 77's original torpedo tubes were destroyed or damaged by French troops.[33] Along with three other 250t-class T-group boats, 76, 77 and 78, and four 250t-class F-group boats, she served with the Royal Yugoslav Navy (Serbo-Croatian Latin: Kraljevska mornarica, KM; Краљевска морнарица). Taken over in March 1921 when French forces withdrew,[31][33] in KM service, 79 was renamed T4.[2] At the outset, she and the other seven 250t-class boats were the only modern sea-going vessels in the KM.[34]

New torpedo tubes of the same size were ordered from the Strojne Tovarne factory in Ljubljana.[5] In KM service it was intended to replace one or both guns on each boat of the 250t class with a longer Škoda 66 mm L/45 gun, and it is believed that this included the forward gun on T4.[5] She was also fitted with one or two Zbrojovka 15 mm (0.59 in) machine guns. In KM service, the crew increased to 52,[5] and she was commissioned in 1923.[35] In 1925, exercises were conducted off the Dalmatian coast, involving the majority of the KM.[36] During a 1927 refit T4 was re-armed with a pair of Škoda 75 mm (3.0 in) L/30 guns that had been manufactured as deck guns for submarines, and were procured from the Škoda works in Plzeň, Czechoslovakia.[37] In May and June 1929, six of the eight 250t-class torpedo boats accompanied the light cruiser Dalmacija, the submarine tender Hvar and the submarines Hrabri and Nebojša, on a cruise to Malta, the Greek island of Corfu in the Ionian Sea, and Bizerte in the French protectorate of Tunisia. The ships and their crews made a very good impression on the British while visiting Malta.[38] In 1932, the British naval attaché reported that Yugoslav ships engaged in few exercises, manoeuvres or gunnery training due to reduced budgets.[39] In the same year, T4 ran aground on the island of Drvenik Mali off the central Dalmatian coast. The hull broke in half, and while the bow initially remained on the island, the stern was towed to the Tivat Arsenal in the Bay of Kotor. As a result, it became a standing joke among KM sailors that T4 was the "world's longest torpedo boat". Eventually both sections were scrapped.[40]