The 250t class were high-seas torpedo boats built for the Austro-Hungarian Navy between 1913 and 1916. A total of 27 boats were built by three shipbuilding companies, with the letter after the boat number indicating the manufacturer. There were small variations between manufacturers, mainly in the steam turbines used, and whether they had one or two funnels. The eight boats of the T-group, designated 74 T – 81 T, were built by Stabilimento Tecnico Triestino, located at Triest. The sixteen boats of the F-group, 82 F – 97 F, were built by Ganz-Danubius at their shipyards at Fiume and Porto Re. The three M-group boats, 98 M – 100 M, were manufactured by Cantiere Navale Triestino at Monfalcone.
All 27 boats saw service in World War I, undertaking anti-submarine operations in the Adriatic Sea, shore bombardment missions along its Italian coastline, and convoy, escort and minesweeping tasks. Although widely used during the war, the class suffered no losses, despite taking hits during surface engagements and damage from accidents. In 1917, some of the guns on the boats were placed on anti-aircraft mounts. Under the terms of the post-war Treaty of Saint-Germain-en-Laye, the boats were transferred to various countries, including seven to Romania, six to Portugal, six to Greece, and eight to the newly created Kingdom of Serbs, Croats and Slovenes (later Yugoslavia). By 1940, thirteen boats of the class had been lost or scrapped, including all six Portuguese boats.
During World War II, the five remaining Greek boats were sunk by Axis aircraft during the German-led invasion of Greece in April 1941. One Romanian boat was lost during the war, while the two remaining Romanian boats performed escort tasks in the Black Sea before being taken over by the Soviet Navy, and serving in the Black Sea Fleet until the end of the war; they were finally stricken in late 1945.
The six surviving Yugoslav boats were captured by the Italians during the Axis invasion of Yugoslavia in April 1941, and were operated by the Regia Marina in a coastal and second-line escort role. Immediately following the Italian capitulation in September 1943, one ex-Yugoslav boat was sunk by German aircraft while attempting to escape to Allied-held southern Italy, another was scuttled by its Italian crew when it had insufficient fuel to escape, and two more escaped and were transferred back into Yugoslav hands a few months later. The remaining two were seized by the Germans. Of these, both were operated by Croatian crews or by the Navy of the Independent State of Croatia for some time before being recovered by the Germans. One was destroyed by Royal Navy Motor Torpedo Boats in June 1944, and the other was sunk by Royal Air Force aircraft in 1945. The two surviving boats were commissioned by the Yugoslav Navy after the war, one continuing in service until the early 1960s.
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 .
Description and construction Stabilimento Tecnico Triestino (STT) of Triest was selected for the contract to build eight vessels, ahead of one other tenderer. 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. The STT boats used Parsons turbines driving two propeller shafts. Another tender was requested for four more boats, but when Ganz-Danubius reduced their price by ten percent, a total of sixteen boats were ordered from them. These boats were powered by AEG-Curtiss turbines, and had two funnels rather than the single funnel of the STT boats. The third contract went to Cantiere Navale Triestino (CNT), who used Melms-Pfenniger turbines, and their boats also had two funnels. The boats of all three groups used steam generated by two Yarrow water-tube boilers, one of which burned fuel oil and the other coal.
The boats of the class were fast and agile, well designed for service in the Adriatic. The M-group boats were longer overall and had a longer forecastle than the T- and F- group boats. All boats of the class had a slight flare at the bow, a straight stem and keel, and a rounded stern. Until October 1915, the boats were painted black, but from that point they were painted a light blue-grey. The hulls were built with a series of 13 transverse bulkheads dividing them into 14 watertight compartments. The forward collision compartment and anchor chain locker were in the fore, abaft of which were two larger accommodation compartments for the enlisted crew, then the forward and aft boiler rooms, the forward and aft turbine rooms, accommodation for officers and non-commissioned officers, and the equipment room was located in the stern. The first two groups had a semi-balanced rudder, whereas the M-group boats had a fully balanced rudder.
The T-group boats were originally to be armed with three guns, and three torpedo tubesone twin and one singlebut this was changed to two guns and four torpedo tubesconsisting of two twin mountingsbefore the first boat was completed, to standardise the armament with the F group to follow. When completed, all 27 boats were armed with two Škoda L/30 guns. They were installed on anti-torpedo boat ( or TAG) mountsfore and aftwithout gun shields, and fired a shell at a muzzle velocity of to a maximum range of at an elevation of 25 degrees. A total of 216 shells were carried for each gun. On the T- and F- group boats, the forward torpedo tubes were mounted between the forecastle and bridge, and on the M-group boats, they were mounted on the aft section of the extended forecastle. On the T-group boats the aft torpedo tubes were located directly abaft the mainmast, and on the F-group boats they were mounted on the quarterdeck, abaft the ship's boat. On the M group boats, the aft torpedo tubes were mounted immediately forward of the aft mast. The torpedo tubes were manufactured by the Whitehead Torpedo Factory in Fiume, and fired the Whitehead 450 mm L/5 torpedo, which was long and weighed with a warhead. At a range of the torpedo could reach a maximum speed of , and at a range of they could travel at . A searchlight was mounted above the bridge. In July 1914, 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. Each vessel could carry 10–12 naval mines.
T-group The T-group were built by STT at the Port of Triest between April 1913 and December 1914. They had a waterline length of , a beam of , and a normal draught of . While their designed displacement was , they displaced about fully loaded. Their Parsons turbines were rated at and 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 boats were originally to be armed with three guns, and three torpedo tubesone twin and one singlebut this was changed to two guns and four torpedo tubesconsisting of two twin mountingsbefore the first boat was completed, to standardise the armament with the F group to follow. The torpedo tubes were mounted in pairs, with one pair mounted between the forecastle and bridge, and the other on a section of raised superstructure above the aft machinery room.
+ Construction of T-group torpedo boats Name Laid down Launched Commissioned 74 T 16 April 1913 28 August 1913 17 June 1914 75 T 28 May 1913 20 November 1913 11 July 1914 76 T 24 August 1913 15 December 1913 20 July 1914 77 T 24 August 1913 30 January 1914 11 August 1914 78 T 22 October 1913 4 March 1914 23 August 1914 79 T 1 December 1913 30 April 1914 1 October 1914 80 T 19 December 1913 3 August 1914 8 November 1914 81 T 6 February 1914 6 August 1914 2 December 1914 When 74 Ts turbines were initially installed, they suffered a major problem with heat expansion of the turbine blades, causing friction between the rotor and stator blades. The issue was so significant that her turbines had to be rebuilt, with additional space between the blades and improved fixing of the rotor blades. Having been first commissioned on 1 February 1914, 74 T was commissioned for a second time on 17 June. Likewise, the next two boats of the T-group had to have their turbines removed, modified and reinstalled due to these issues.
F-group The F-group were built by Ganz & Danubius at Fiume and nearby Porto Re between October 1913 and December 1916. They had a waterline length of , a beam of , and a normal draught of . While their designed displacement was , they displaced about fully loaded. The crew consisted of 38 officers and enlisted men. Their AEG-Curtiss turbines were rated at with a maximum output of , and the boats were designed to reach a top speed of . During trials, 93 F produced , and reached a top speed of . They carried of coal and of fuel oil, which gave them a range of at .
+ Construction of F-group torpedo boats Name Laid down Launched Completed 82 F 30 October 1913 11 August 1914 16 August 1916 83 F 17 November 1913 7 November 1914 7 August 1915 84 F 27 November 1913 21 November 1914 2 November 1916 85 F 7 January 1914 5 December 1914 19 December 1915 86 F 26 January 1914 19 December 1914 23 May 1916 87 F 5 March 1914 20 March 1915 25 October 1915 88 F 7 March 1914 24 April 1915 30 November 1915 89 F 13 May 1914 12 May 1915 1 March 1916 90 F 9 September 1914 28 May 1915 8 August 1916 91 F 24 November 1914 21 June 1916 11 July 1916 92 F 30 November 1914 29 September 1916 23 March 1916 93 F 9 January 1915 25 November 1915 16 April 1916 94 F 19 January 1915 8 March 1916 17 June 1916 95 F 9 February 1915 24 June 1916 27 September 1916 96 F 24 February 1915 7 July 1916 23 November 1916 97 F 5 March 1915 20 August 1916 22 December 1916 When Italy declared war on Austria-Hungary in May 1915, five incomplete F-group boats were towed to be completed in safety. 82 F, 83 F and 84 F were taken from Porto Re to Pola, and 90 F and 91 F were taken to Novigrad. This resulted in delays to the completion of these boats.
M-group The M-group were built by CNT at Monfalcone between March 1914 and March 1916. They had a waterline length of , a beam of , and a normal draught of . Their designed displacement was , and they displaced about fully loaded. The crew consisted of 38 officers and enlisted men. Their Melms-Pfenniger turbines were rated at with a maximum output of , and the boats were designed to reach a top speed of . They carried enough coal and fuel oil to give them a range of at .