SM U-28 or U-XXVIII was a U-boat or submarine for the Austro-Hungarian Navy. U-28, built by the Austrian firm of Cantiere Navale Triestino (CNT) at the Pola Navy Yard, was launched in January 1917 and commissioned in June.

She had a single hull and was just over in length. She displaced nearly when surfaced and over when submerged. Her two diesel engines moved her at up to on the surface, while her twin electric motors propelled her up to while underwater. She was armed with two bow torpedo tubes and could carry a load of up to four torpedoes. She was also equipped with a deck gun and a machine gun.

During her service career, U-28 sank the British Q-ship HMS and nine other ships, sending a combined tonnage of 44,743 to the bottom. U-28 was surrendered at Venice in 1919, granted to Italy as a war reparation and broken up the following year.

Design and construction Austria-Hungary's U-boat fleet was largely obsolete at the outbreak of World War I.Gardiner, p. 341. The Austro-Hungarian Navy satisfied its most urgent needs by purchasing five Type UB I submarines that comprised the from Germany,Gardiner, p. 343. by raising and recommissioning the sunken French submarine as , had been caught in an anti-submarine net while trying to enter the harbor at Pola on 20 December 1914. See: Gardiner, p. 343. and by building four submarines of the that were based on the 1911 Danish .Gardiner, p. 344.The plans for the Danish s, three of which were built in Austria-Hungary, were seized from Whitehead & Co. in Fiume. See: Gardiner, pp. 344, 354.

After these steps alleviated their most urgent needs, the Austro-Hungarian Navy selected the German Type UB II design for its newest submarines in mid 1915.Halpern, p. 383. The Germans were reluctant to allocate any of their wartime resources to Austro-Hungarian construction, but were willing to sell plans for up to six of the UB II boats to be constructed under license in Austria-Hungary. The Navy agreed to the proposal and purchased the plans from AG Weser of Bremen.Baumgartner and Sieche, as excerpted here (reprinted and translated into English by Sieche). Retrieved 1 December 2008.

U-28 displaced surfaced and submerged. She had a single hull with saddle tanks,Gardiner, p. 181. and was long with a beam of and a draft of . For propulsion, she had two shafts, twin diesel engines of for surface running, and twin electric motors of for submerged travel. She was capable of while surfaced and while submerged. Although there is no specific notation of a range for U-28 in Conway's All the World's Fighting Ships 1906–1921, the German UB II boats, upon which the U-27 class was based, had a range of over at surfaced, and at submerged. U-27-class boats were designed for a crew of 23–24.

U-28 was armed with two bow torpedo tubes and could carry a complement of four torpedoes. She was also equipped with a /26 caliber deck gun and an machine gun.

After intricate political negotiations to allocate production of the class between Austrian and Hungarian firms, U-28 was ordered from Cantiere Navale Triestino (CNT) on 12 October 1915. She was laid down by early 1916 at the Pola Navy Yard,By this time, the CNT shipyards at Monfalcone had been overrun by the Italian Army. See: Baumgartner and Sieche, as excerpted here (reprinted and translated into English by Sieche). Retrieved 17 January 2008. and launched on 8 January 1917.

Service career After her completion, U-28 was commissioned into the Austro-Hungarian Navy on 26 June 1917 under the command of Linienschiffsleutnant Zdenko Hudeček. Previously in command of , Hudeček was a 30-year-old native of Theresienstadt (present-day Terezín in the Czech Republic). Four days after the U-boat's commissioning, Hudeček achieved his first kill at the helm of U-28. On 30 June, while on patrol about east of Malta, U-28 came upon the 4,809 GRT British steamer Haigh Hall. The turret hull ship was carrying wheat from Bombay to Naples when torpedoed and sunk by Hudeček. Three days later, the British India passenger ship met the same fate. Even though escorted by an Italian destroyer and a trawler,Gibson and Prendergast, p. 258. Mongara was torpedoed and sunk by U-28 just from the breakwater at Messina. The 8,205 GRT liner—the largest ship sunk by U-28—was en route from Sydney to London when she went down, but was spared any loss of life in the attack. In eight days in commission, U-28s tally was over 13,000 GRT, already exceeding the totals of all four U-boats of the .Gardiner, p. 341.

The following month, U-28 sank the 3,881 GRT collier Maston from Cape Spartivento, Calabria, on 13 August, killing two men of the British ship's crew. Three days after Maston went down, U-28 sank HMS Bradford City, a 3,683 GRT British Q ship in the Straits of Messina, with no loss of life. HMS Bradford City, operating under the pseudonym Saros, had been particularly detached to the Straits to hunt U-28 and had ignored orders to proceed to port from officers unaware of her naval status. After the torpedo struck, the ship's "panic party" had taken to the boats in the hope of luring her attacker to the surface, but the arrival of the French naval trawler Hiver drove U-28 away before the gun crews aboard HMS Bradford City could engage the submarine. HMS Bradford City sank within 30 minutes off San Remo.Hepper, p. 101. In October, U-28 closed out her 1917 list of victims with Bontnewydd, a British steamer sunk north-northeast of Susa. The 3,296 GRT steamer was sailing in ballast from Marseille for Karachi.

In January 1918, U-28 sank an additional three ships. Bosforo, an Italian steamer of 2,723 GRT headed for Salonika, was sent to the bottom near Cape Spartivento on 12 January. The following day, U-28 dispatched the British steamer Rapallo south of Cape Peloro. One sailor aboard the one-year-old ship died in the attack, which occurred while the ship was headed to Messina in ballast. On 21 January, West Wales, a collier headed from Barry to Alexandria, was sunk from Malta, taking her load of coal and two of her crew to the bottom.

On 8 March, U-28 attacked two ships, sinking one of them. The first ship, Mitra, a 5,592 GRT tanker was hit by U-28 but was able to make port in Malta with her cargo of oil.Mitra lived somewhat of a charmed life. The 1912 ship had survived the explosion of a mine laid by German U-boat in June 1917, in addition to weathering the attack from U-28. The ship, renamed Liberatador in 1935, remained in service until 1950, when she was scrapped at Buenos Aires. See: Later in the month, U-28 sank from Linosa, killing one sailor in the attack. The 1905 British ship was carrying cotton and cottonseed from Alexandria for London when the attack occurred. Three days later, Stolt Nielsen, a 5,684 GRT steamship, was sent to the bottom from Malta. Carrying a general cargo for the Admiralty when she went down, the British ship turned out to be the final ship to be sunk by U-28.

At the war's end, U-28 was surrendered to Italy at Venice in 1919. Later awarded to Italy as a war reparation, she was scrapped at Venice in 1920. In her 18-month career, U-28 sank ten ships with a combined tonnage of 44,743, and damaged an eleventh.

Summary of raiding history +Ships sunk or damaged by SM U-28DateNameNationalityTonnageMerchant ship tonnages are in gross register tons. Military vessels are listed by tons displacement.Fate30 June 1917Haigh Hall4,809Sunk3 July 1917Mongara8,205Sunk13 August 1917Maston3,881Sunk16 August 1917HMS Bradford City3,683Sunk5 October 1917Bontnewydd3,296Sunk12 January 1918Bosforo2,723Sunk13 January 1918Rapallo3,811Sunk21 January 1918West Wales4,336Sunk8 March 1918Mitra5,592Damaged8 March 1918Uganda4,315Sunk11 March 1918Stolt Nielsen5,684Sunk Sunk:Damaged:Total:44,7435,59250,335

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