SM U-15 or U-XV was a or U-boat of the Austro-Hungarian Navy ( or ) during World War I. U-15 was constructed in Germany and shipped by rail to Pola where she was assembled and launched in April 1915. She was commissioned in October 1915. U-15 was the most successful boat of the U-10 class, sinking six ships totaling and 745 tons. The boat survived the war and was handed over to Italy as a war reparation and scrapped in 1920.

Design and construction U-15 was constructed at AG Weser in Bremen for the Austro-Hungarian Navy and then shipped by rail in sections to the navy yard at Pola, where the sections were riveted together. Though there is no specific mention of how long it took for U-15s sections to be assembled, a sister boat, the German Type UB I submarine UB-3, shipped to Pola from Germany in mid-April 1915, was assembled in about two weeks.Messimer, p. 126–27.The Austro-Hungarian and the German Type UB I were virtually identical. U-15 was launched in April.

U-15 was a small, coastal submarine that displaced surfaced and submerged. She featured a single shaft, a single Daimler diesel engine for surface running, and a single electric motor for submerged travel. U-15 was capable of up to while surfaced and while submerged at a diving depth of up to . She was designed for a crew of 17 officers and men.

U-15 was equipped with two torpedo tubes located in the front and carried a complement of two torpedoes. In October 1916, U-15s armament was supplemented with a 37 mm/23 (1.5 in) quick-firing (QF) gun. This gun was replaced by a /33 QF gun in November 1917.

Operational history SM U-15 was commissioned into the Austro-Hungarian Navy on 6 October under the command of Linienschiffsleutnant Friedrich Schlosser. On 28 November, Linienschiffsleutnant Friedrich Fähndrich was assigned to the first of two stints in command of the boat. On 18 December, Fähndrich and U-15 attacked and sank two Albanian sailing vessels near Lezhë. The Erzen, of , and the Figlio Preligiona, of , were both sunk at position . After being relieved by Linienschiffsleutnant Franz Rzemenowsky von Trautenegg from late March to early May 1916, Fähndrich resumed command on 10 May. One week later, on 17 May, U-15 torpedoed and sank the Italian steamer in the Adriatic some east of Brindisi.Stura, launched in 1883, had sailed in passenger duty for Navigazione Generale Italiana between the Mediterranean and New York before the war. See: Immigration Information Bureau, pp. 8–9, 16, 23.

The following month, Fähndrich and the crew of U-15 scored their second double kill when they sank the Italian auxiliary cruiser () and the French destroyer Fourche (745 tons). While about east of Otranto on 23 June, U-15 torpedoed and sank Cittá di Messina. The escorting destroyer Fourche began a depth charge attack on U-15 and assumed success when an oil slick appeared on the surface. After the captain of Fourche turned his attentions to the rescue Cittá di Messinas survivors, U-15 launched a single torpedo that struck Fourche amidships and sank her.Compton-Hall, p. 230.

On 25 October, U-15, back under the command of von Trautenegg, sank the Italian steamer , Helgason refers to the ship as "Polceverra", but Haworth, and Swiggum & Kohli identify the ship as "Polcevera".For Haworth, see: For Swiggum & Kohli, see: a sister ship to Stura (sunk by U-15 in May). Polcevera was the last ship sunk by U-15.

From October 1916 to the end of the fighting in November 1918, U-15s activities are unknown. U-15 was at Pola at the end of the war when Austria-Hungary handed her over to Italy.Gibson and Pendergast, p. 388. U-15 was scrapped at Pola by 1920.

Summary of raiding history DateNameNationalityTonnageMerchant ship tonnages are in gross register tons. Military vessels are listed by tons displacement.Fate18 December 1915Erzen25Sunk18 December 1915Figlio Preligiona80Sunk17 May 1916Stura2,237Sunk23 June 1916Citta Di Messina3,495Sunk23 June 1916745Sunk25 October 1916Polceverra2,207SunkTotal:8,789

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