Yugoslav torpedo boat T7

The Yugoslav torpedo boat T7 was a sea-going torpedo boat that was operated by the Royal Yugoslav Navy between 1921 and 1941. Originally built as 96 F, a 250t-class torpedo boat built for the Austro-Hungarian Navy in 1915–16, she was armed with two 66 mm guns and four 450 mm torpedo tubes, and could carry 10–12 naval mines. She saw active service during World War I, performing convoy, patrol, escort and minesweeping tasks, and anti-submarine operations. Following Austria-Hungary's defeat in 1918, 96 F was allocated to the Navy of the Kingdom of Serbs, Croats and Slovenes, which became the Royal Yugoslav Navy, and was renamed T7.

During the German-led Axis invasion of Yugoslavia in April 1941, the vessel was captured by the Italians and served with the Royal Italian Navy under her Yugoslav designation, conducting coastal and second-line escort duties in the Adriatic. Following the Italian capitulation in September 1943, she was handed over by the Germans to the Navy of the Independent State of Croatia. She was sunk by British motor torpedo boats in June 1944.

Background
In 1910, the Austria-Hungary Naval Technical Committee initiated the design and development of a 275 LT coastal torpedo boat, specifying that it should be capable of sustaining 30 kn for 10 hours. This specification was based 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 (kaiserliche und königliche Kriegsmarine) base at the Bay of Kotor (Bocche di Cattaro) 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. Stabilimento Tecnico Triestino (STT) of Trieste was selected for the contract to build the first eight vessels, designated the T-group. 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, designated the F-group. The F-group designation signified the location of Ganz & Danubius' main shipyard at Fiume.

Description and construction
The 250t-class F-group boats had a waterline length of 58.5 m, a beam of 5.8 m, and a normal draught of 1.5 m. While their designed displacement was 266 t, they displaced about 330 t fully loaded. The crew consisted of 38–41 officers and enlisted men. The boats were powered by two AEG-Curtiss steam turbines driving two propellers, using steam generated by two Yarrow water-tube boilers, one of which burned fuel oil and the other coal. The turbines were rated at 5000 shp with maximum output of 5000 shp with a maximum output of 6000 shp, and were designed to propel the boats to a top speed of 28 kn. They carried 20 t of coal and 34 t of fuel oil, which gave them a range of 1200 nmi at 16 kn. The F-group had two funnels rather than the single funnel of the T-group. Despite the specifications of the contract being very close to the requirements for the coastal torpedo boat, the Ganz & Danubius boats were classified as sea-going. The 250t-class were the first small Austro-Hungarian Navy boats to use turbines, and this contributed to ongoing problems with them.

The boats were armed with two Škoda 66 mm L/30 guns, and four 450 mm torpedo tubes. They could also carry 10–12 naval mines. 96 F was the second-to-last of its group to be completed, and was laid down on 24 February 1915, launched on 7 July 1916 and completed on 23 November of that year.

World War I and the interwar period
During World War I, 96 F was used for convoy, patrol, escort and minesweeping tasks, and anti-submarine operations. Due to inadequate funding, 96 F and the rest of the 250t class were essentially coastal vessels, despite the original intention that they would be used for "high seas" operations. In 1917, one of the 66 mm guns on each boat was placed on an anti-aircraft mount. On the night of 11 May 1917, the SMS Csikós, accompanied by 96 F and two other 250t-class boats, were pursued in the northern Adriatic by an Italian force of five destroyers, but were able to retire to safety behind a minefield. On 3 June, the destroyers SMS Wildfang and Csikós, along with 96 F and another 250t-class boat, had a brief encounter with three Italian MAS boats off the mouth of the Tagliamento river in the far north of the Adriatic.

96 F survived the war intact. In 1920, under the terms of the previous year's Treaty of Saint-Germain-en-Laye, she was allocated to the Kingdom of Serbs, Croats and Slovenes (KSCS, later Yugoslavia). Along with three other 250t-class F-group boats, 87 F, 93 F and 97 F, and four 250t-class T-group boats, she served with the Royal Yugoslav Navy (Kraljevska Jugoslovenska Ratna Mornarica, KJRM; Кpaљeвcкa Југословенска Pатна Морнарица). Transferred in March 1921, in KJRM service, 96 F was renamed T7. At the outset, she and the other seven 250t-class boats were the only modern sea-going vessels in the KJRM. In 1925, exercises were conducted off the Dalmatian coast, involving the majority of the navy. In May – June 1929, six of the eight 250t-class torpedo boats accompanied the light cruiser Dalmacija, the submarine tender Hvar and the submarines YUGOSLAV SUBMARINE Hrabri and YUGOSLAV SUBMARINE Nebojša, on a cruise to Malta, the Greek island of Corfu in the Ionian Sea, and Bizerte in the French protectorate of Tunisia. It is not clear if T7 was one of the torpedo boats involved. The ships and crews made a very good impression while visiting Malta. In 1932, the British naval attaché reported that Yugoslav ships engaged in few exercises, manoeuvres or gunnery training due to reduced budgets.

World War II
In April 1941, Yugoslavia entered World War II when it was invaded by the German-led Axis powers. At the time of the invasion, T7 was assigned as the flagship of the 3rd Torpedo Division located at Šibenik, which included her three former F-group sisters. On 8 April, the four boats of the 3rd Torpedo Division, along with other vessels, were tasked to support an attack on the Italian enclave of Zadar on the Dalmatia coast. They were subjected to three Italian air attacks and, after the last one, sailed from the area of Zaton into Lake Prokljan, where they remained until 11 April. On 12 April, the 3rd Torpedo Division arrived at Milna on the island of Brač, and refused to follow orders to sail to the Bay of Kotor. All four F-group boats, including T7, were then captured by the Italians.

T7 was then operated by the Italians under her Yugoslav designation, conducting coastal and second-line escort duties in the Adriatic. Her guns were replaced by two 76 mm L/40 anti-aircraft guns, but no other significant alterations was made to her. After the Italians capitulated in September 1943, once under German control, T7 was handed over to the Navy of the Independent State of Croatia, and served under her Yugoslav designation. Her crew came under the influence of the Yugoslav Partisans, and were preparing to mutiny when the Germans intervened. On 24 June 1944, she and the German S-boats S 154 and S 157 of the 7th S-Boat Flotilla were sailing between Šibenik and Rijeka, protecting German sea supply routes along the Adriatic, when they were attacked by the Royal Navy Fairmile D motor torpedo boats MTB 659, MTB 662 and MTB 670 near the island of Kukuljari, south of Murter Island. The MTBs fired two torpedoes at T7, but missed, so they closed and engaged her with their guns, setting her ablaze. She was beached, and 21 crew were rescued by the MTBs. The British crews later examined the wreck, capturing five more crew, then destroyed her with demolition charges.