"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 75 mm/26 (3.0 in) 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, and launched on 8 January 1917. 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-ton 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, "Mongara" was torpedoed and sunk by "U-28" just from the breakwater at Messina. The 8,205-ton 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-28"s tally was over 13,000 tons, already exceeding the totals of all four U-boats of the . The following month, "U-28" sank the 3,881-ton 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 "Bradford City", a 3,683-ton British Q ship in the Straits of Messina, with no loss of life. "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.