Miklos Horthy de Nagybanya, who became the rear admiral of the Austro-Hungarian fleet in 1918, decided to activate the fleet and use it in a large naval operation against the Otranto Barrage. The attack was planned for June 1918, together with the operations of the Austrian army at the Italian (Soca) front.
Horthy's plan was too complicated. Horthy decided to use as much ships as possible, so that the crews would get some experience. There were to be two attack groups and seven support groups. The battleships left Pula in two groups, and due to small number of escort ships (destroyers and torpedo-boats) were poorly protected. SMS Viribus Unitis (with admiral Horthy aboard) and SMS Prinz Eugen left Pula with five escort ships on June 8th 1918, and headed for the south. The battleships SMS Szent István and Tegetthoff left Pula on June 9th in the evening, escorted by one destroyer and six torpedo-boats. They were late because the guards on the harbour entrance had not removed the barricades on time. To compensate the lost time, it was ordered that all the ships in the group increase the speed to 16 knots. However, the engines of the Szent István started overheating, so the speed was reduced to 12 knots. After a second attempt to increase the speed, the Szent István started smoking a lot, which made her visible to another, enemy group of ships.
A map of Croatia showing the place where SMS Szent István sank.
In the dawn of June 10th 1918 battleships SMS Szent István and Tegetthoff unexpectedly met Italian torpedo-boats, near the island Premuda. The Italian torpedo-boats MAS - 15 and MAS - 21 were on a mission that night, measuring the depth of sea near Premuda and looking for mines (to enable the operations of their own submarines). The Italian commander, Luigi Rizzo, had previously, on December 10th 1917, sunk the Austro-Hungarian ironclad SMS Wien (Monarch class). MAS - 21 attacked the Tegetthoff, but the first torpedo did not even leave its casing and the second one did not explode. The Szent István was hit by two torpedoes launched by MAS - 15 at 3:31 AM. The Italian torpedo-boats managed to escape, leaving the Austro-Hungarian task force shooting aimlessly at the surrounding sea.
The Szent István was severely damaged. The torpedoes had damaged the outer hull and the bulkhead between the boiler rooms (the biggest rooms below decks), so the ship was flooding quickly. Only two boilers remained lit, providing steam for electrical generators, and, thereby, electricity for the pumps. The attempt to beach the ship by hauling her to the nearby island Molat, failed. All main guns were turned to the left side to reduce the listing, but that was in vain. The crew received the final, the saddest and most difficult order: "Schiff verlassen! Los vom Schiff! (Abandon ship!)" The Austro-Hungarian newest battleship capsized and sank at 6:12 AM, after three hours of agony, taking along with it 89 sailors, including those who had been keeping the last two boilers lit. The sinking was filmed by a film crew aboard the Tegetthoff. The film was later used for raising money for the Red Cross. There are many copies, and it is one of the two films showing the loss of a battleship on the high seas, the second one showing the sinking of HMS Barham in World War II. After the sinking of the Szent István the operation was aborted and all the ships returned to Pula, where they remained until the war ended.
The various stages of sinking of SMS Szent István.
The wreck of SMS Szent István (at the depth of 66 metres) was visited several times, from 1990 to 1998 by Austrian, Croatian and Hungarian divers. The wreck lies turned upside down, with her turrets still turned to the left side. The divers found four holes on the hull, but only two of them could be the result of the explosions of the torpedoes. The third one could have been made by a torpedo that did not explode, while the fourth one was probably made when the ship hit the bottom. The bow is broken off, so the divers visited the forward ammunition magazine. The brass letters from the stern, once proudly showing the ship's name, are now in the museum in Pula, as well as all other recovered remains of the ship.