Viribus Unitis was the first Austrian dreadnought, commissioned in December 1912. Viribus Unitis carried 12 12″ guns in four triple superfiring turrets, giving her a 12 gun broadside and 6 gun end on fire. She could make 20 knots, but displaced only 20000 tons. Although reasonably well protected from surface fire, Viribus Unitis had very poor underwater protection and was vulnerable to torpedo attack. Early on in the design process, German engineers recommended that the top two turrets be reduced from three to two guns, and that the weight saving be used to shore up her compartmentation. Unfortunately, this advice was rejected.
Austria-Hungary was reluctant to use Viribus Unitis and her sisters aggressively. The German Navy requested the deployment of the three dreadnoughts in August 1914 to support Goeben. However, because Austria-Hungary hoped to remain at peace with the United Kingdom, and because the Austrians feared that a big naval display would bring Italy into the war, the request was declined. This must be regarded as a poor strategic decision; VU and her sisters would play virtually no role in the war after 1914, and early vigorous employment might have damaged the Royal Navy. Neither Admiral Troubridge’s force of four armored cruisers nor the battlecruisers Indomitable and Inflexible (chasing Goeben at the time) would have stood much chance against the Austrian ships.
The rest of Viribus Unitis’ career was uneventful. In May 1915, she bombarded the Italian port city Ancona. In 1918, she and her three sisters sortied to attack the Otranto Barrage, a set of defenses designed to seal the Adriatic off and trap the Austrian Navy. Szent Istvan, one of VU’s sisters, was struck by two torpedos and sank, leading to the cancellation of the operation. Viribis Unitis returned to port, where she sat while Austria-Hungary disintegrated.
In late October 1918, Croatia and Slovenia severed their connection to the Hapsburg crown. Emperor Karl I, a stand up guy when he wasn’t ordering the gassing of his enemies, turned over the entire Austrian Navy to the state that would (eventually) become Yugoslavia. The Allies, however, refused to recognize this transfer. The Italians in particular were not enthusiastic about the creation of a new, large Slavic state with a large and powerful navy. On October 31st, two Italian frogmen entered Pula harbor and attached a mine to Viribus Unitis’ hull. The two frogmen were captured before the mine exploded, and brought aboard the Croatian battleships. When questioned, they admitted that they had attached a mine, and recommended that the ship be abandoned. Panic and frenzy ensued, with the Croatian sailors understandably irritated at the Italians. The ship was partially abandoned and the mine exploded. 300 sailors who had remained on board for damage control, as well as the admiral of the Croatian Navy, died when the ship capsized.
Most of the wreck of Viribus Unitis remains at the bottom of Pula Harbor. A more detailed description of her loss can be found here.
Trivia: What battleship was capable of launching 22 aircraft?