T5 was a sea-going torpedo boat operated by the Royal Yugoslav Navy between 1921 and 1941. Originally 87 F, a 250t-class torpedo boat of the Austro-Hungarian Navy built in 1914–1915, she was armed with two guns and four torpedo tubes, and could carry 10–12 naval mines. She saw active service during World War I, performing convoy, patrol, escort and minesweeping tasks, anti-submarine operations and shore bombardment missions. In 1917 the suffixes of all Austro-Hungarian torpedo boats were removed, and thereafter she was referred to as 87. She was part of the escort force for the Austro-Hungarian dreadnought during the action that resulted in the sinking of that ship by Italian torpedo boats in June 1918, and rescued many of her crew.

Following Austria-Hungary's defeat in 1918, 87 was allocated to the Navy of the Kingdom of Serbs, Croats and Slovenes, which later became the Royal Yugoslav Navy, and was renamed T5. At the time, she and the seven other 250t-class boats were the only modern sea-going vessels of the fledgling maritime force. During the interwar period, T5 and the rest of the navy were involved in exercises of training and cruises to friendly ports, but activity was limited by reduced naval budgets. The boat was captured by the Italians during the German-led Axis invasion of Yugoslavia in April 1941. After her main armament was modernised, she served with the Royal Italian Navy under her Yugoslav designation, conducting coastal and second-line escort duties in the Adriatic Sea. Following the Italian capitulation in September 1943, she was returned to the Royal Yugoslav Navy-in-exile and continued serving as T5. At the end of the war, she was transferred to the new Yugoslav Navy and served as Cer in guard ship, patrol ship and training ship roles until she was stricken off the naval register in 1963 and scrapped soon after.

Background In 1910, the Austria-Hungary Naval Technical Committee initiated the design and development of a coastal torpedo boat, specifying that it should be capable of sustaining for 10 hours. At the same time, the committee issued design parameters for a high seas or fleet torpedo boat of , top speed of 30 kn and endurance of . This design would have been a larger and better-armed vessel than the existing Austro-Hungarian s. The specification for the high seas torpedo boat was based on an expectation that the Strait of Otranto, where the Adriatic Sea meets the Ionian Sea, would be blockaded by hostile forces during a future conflict. In such circumstances, there would be a need for a torpedo boat that could sail from the Austro-Hungarian Navy (, ) base at the Bocche di Cattaro (the Bocche or Bay of Kotor) to the strait during the night, locate and attack blockading ships and return to port before morning. Steam turbine power was selected for propulsion, as diesels with the necessary power were not available, and the Austro-Hungarian Navy did not have the practical experience to run turbo-electric boats. Despite having developed these ideas, the Austro-Hungarian Navy then asked shipyards to submit proposals for a boat with a maximum speed of . Stabilimento Tecnico Triestino (STT) of Trieste was selected for the contract to build the first eight vessels, designated as the T-group. Another tender was requested for four more boats, but when Ganz & Danubius reduced their price by ten per cent, a total of sixteen boats were ordered from them, designated the F-group. The F-group designation signified the location of Ganz & Danubius' main shipyard at Fiume.

Description and construction

The F-group boats had short raised forecastles and an open bridge, and were fast and agile, well designed for service in the Adriatic. They had a waterline length of , a beam of , and a normal draught of . While their designed displacement was , they displaced fully loaded. The boats were powered by two AEG-Curtis steam turbines driving two propellers, using steam generated by two Yarrow water-tube boilers, one of which burned fuel oil and the other coal. There were two boiler rooms, one behind the other. The turbines were rated at with a maximum output of and were designed to propel the boats to a top speed of . They carried of coal and of fuel oil, which gave them a range of at . The F-group had two funnels rather than the single funnel of the T-group. 79 T and the rest of the 250t class were classified as high seas torpedo boats by the Austro-Hungarian Navy, despite being smaller than the original concept for a coastal torpedo boat. The naval historian Zvonimir Freivogel states that this type of situation was common due to the parsimony of the Austro-Hungarian Navy. They were the first small Austro-Hungarian Navy boats to use turbines, and this contributed to ongoing problems with them, which had to be progressively solved once they were in service. The crew consisted of three officers and thirty-eight enlisted men. The vessel carried one yawl as a ship's boat.

The boats were armed with two Škoda L/30 guns, with the forward gun mounted on the forecastle, and the aft gun on the quarterdeck. A searchlight was mounted above the bridge. They were also armed with four torpedo tubes mounted in pairs, with one pair mounted between the forecastle and bridge, and the other aft of the mainmast. They could also carry 10–12 naval mines.

The first of the F-group to be completed at Ganz-Danubius' main shipyard at Fiume, 87 F was laid down on 5 March 1914, launched on 20 March 1915, and commissioned on 28 September. Prior to her commissioning, one Schwarzlose M.7/12 machine gun was included in the armament of all boats of the class for anti-aircraft work. Four mounting points were installed so that the machine gun could be mounted in the most effective position depending on the expected direction of attack.

Career

World War I 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. 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. On 9 December 1915, 87 F, two other 250t-class boats, two s and three destroyers accompanied the protected cruiser to escort Austro-Hungarian seaplanes attacking Ancona. Five days later, Szigetvár led a similar seaplane raid on Rimini, escorted by two destroyers, two Kaiman-class boats, and three 250t-class boats including 87 F.

On 14 January 1916, 87 F laid mines in the Gulf of Triest. On 2 February 87 F, two other 250t-class boats and the Huszár-class destroyer were sent from the main Austro-Hungarian naval base at Polain the northern Adriaticto the Bocche escorting the armoured cruiser and the scout cruiser . The following day this group of vessels conducted a shore bombardment operation against the Italian coast near San Vito Chietino, including the railway line between Ortona and Tollo. During this operation, Sankt Georg exchanged fire with an Italian armed train operated by the Royal Italian Navy (), equipped with guns. On 6 February, Helgoland, 87 F and five other 250t-class boats were sent to intercept the British light cruiser and Italian which had attacked Wildfang while she was escorting a seaplane raid. Instead of meeting the pair that had forced Wildfang to retreat, the Austro-Hungarian force encountered the British light cruiser and French which had since relieved themnorth of Durazzo in Albania. The torpedo boats manoeuvred into two groups of three for the attack, but in one of the groups two leading boats collided, with one sustaining damage, forcing that group to retreat to the port of Budva in Austro-Hungarian-occupied Montenegro, and the other group pressed their attack unsuccessfully. The entire Austro-Hungarian force then returned to the Bocche, having lost an opportunity to interdict significant convoy traffic further south between Albania and Italy.

On 4/5 July 1916, Helgoland led an unproductive raid on the Otranto Barrage, the Allied naval blockade of the Strait of Otranto, escorted by three destroyers, 87 F, and 85 F. On the night of 8/9 July, the scout cruiser led 87 F and two Kaiman-class boats in a more successful raid on the barrage which resulted in the sinking of two drifters, damage to two more, and the capture of nine crew as prisoners of war. The force was chased by Italian destroyers, but escaped with the assistance of Austro-Hungarian seaplanes from the Bocche that attacked the Italian ships. On 15 August, 87 F joined 85 F and two destroyers to search for the missing seaplane L 87, which was located and towed to the Bocche the following day. On 28 August, a large force led by Sankt Georg, the armoured cruiser , Novara and Helgoland, escorted by five destroyers, 87 F and three other 250t-class boats, steamed to the Italian coast in an attempt to draw Italian ships into a trap set with four Austro-Hungarian u-boats. The Italians did not detect the Austro-Hungarian ships due to fog, and the operation was a failure. On 23 September, 87 along with two other 250t-class boats and a Kaiman-class boat laid mines outside the port of Durazzo. On the night of 4/5 October, 87 F and two other 250t-class boats steamed to the barrage but located no targets. On 4 November 1916, three Italian destroyers and three torpedo boats were involved in a brief encounter in the northern Adriatic with two Austro-Hungarian destroyers accompanied by 87 F and two other 250t-class boats. The following day, the same three torpedo boats conducted a shore bombardment of Sant'Elpidio a Mare while en route to Pola which resulted in an artillery duel with an Italian armoured train.