Although the Austrian navy had won a remarkable victory against the Italians at the Battle of Lissa in the Adriatic on 20 July 1866, economic problems following the creation of the Dual Monarchy the following year meant that the new Austro-Hungarian navy had to struggle for funding against the competing demands of the army.
However, from about 1900, the navy began a programme of modernisation with the invaluable support of Kaiser Franz Josef’s heir, the ill-fated Archduke Franz Ferdinand. At this time, the far more powerful Italian navy dominated the Adriatic, but the situation changed with the revolution in naval technology following the launch of HMS Dreadnought in 1906.
All earlier battleships were suddenly obsolescent, and Ferdinand’s influence helped to push through approval for a succession of new vessels, the most important of which were the first Austro-Hungarian dreadnoughts: Viribus Unitis, Tegetthoff, Prinz Eugen, and Szent István – collectively known as the Viribus Unitis-class.
Their design was not finalised until 1909-1910, enough time to incorporate some of the lessons from the first generation of British and German dreadnoughts, notably the adoption of an improved main armament layout of four triple centreline 305mm (12in) gun turrets.
However, despite this firepower, the class had serious weaknesses, including excessively large gaps between the main armament turrets and the armoured barbettes on which they were mounted. Large-calibre shells hitting these ‘shot traps’ could easily jam or even destroy the turrets.
Most seriously, underwater protection and internal subdivision were very poor. The double-bottom was extended upwards to the lower edge of the waterline main armour belt, with a thin 10mm (0.4in) plate as the outermost bulkhead. It was backed by a torpedo bulkhead comprising two 25mm (1in) plates. The total depth of this protection was only 1.6 metres (5ft 3in), which proved insufficient against even light torpedoes.
As the vessels saw little real action until the last months of the war, this vulnerability was not fully appreciated until June 1918, when all four of the class made a rare sortie into the Adriatic. At 03.30 on 10 June, Szent István was hit by two 45cm (18in) torpedoes launched by the Italian motor torpedo boat MAS-15. The aft boiler room quickly flooded, and the ship listed 10° to starboard.
Counter-flooding the portside trim cells and magazines reduced the list to 7°, but the leaks could not be plugged, and the ship had to be stopped to divert power to the pumps. Tegetthoff attempted to take her in tow, but the list steadily worsened until she finally capsized and sank three hours after being hit, with the loss of 89 men.
The vulnerability of the class to underwater damage was demonstrated even more dramatically on 1 November 1918 by an Italian attack on the fleet anchored at Pula on the modern-day Croatian coast. Events were moving so quickly that the Italians were unaware that Viribus Unitis had just been taken over by the newly formed Yugoslav navy and renamed Jugoslavija.
A manned torpedo placed a time-fused mine containing 180kg (400lb) of TNT under the battleship, which ripped a large hole in her hull. She capsized and sank within 15 minutes, with the loss of almost 400 men. •