Characteristics
The ships had an overall length of 152 metres (498 ft 8 in), a beam of 27.9 metres (91 ft 6 in), and a draught of 8.7 metres (28 ft 7 in) at deep load. She displaced 20,000 tonnes (19,684 long tons) at load and 21,689 tonnes (21,346 long tons) at deep load.
The propulsion consisted of four Parsons steam turbines, each of which was housed in a separate engine-room. The turbines were powered by twelve Babcock & Wilcox boilers. The turbines were designed to produce a total of 27,000 shaft horsepower (20,134 kW), which was theoretically enough to attain her designed speed of 20 knots (23 mph; 37 km/h), but no figures from her speed trials are known to exist. She carried 1,844.5 tonnes (1,815.4 long tons) of coal, and an additional 267.2 tonnes (263.0 long tons) of fuel oil that was to be sprayed on the coal to increase its burn rate. At full capacity, she could steam for 4,200 nautical miles (7,800 km) at a speed of 10 knots (12 mph; 19 km/h).
Each ship had an armament consisting of twelve 305-millimetre (12 in)/45-caliber K 10 guns in four triple turrets mounted on the center-line, forward and aft of the superstructure. Their secondary armament consisted of twelve 150-millimetre (5.91 in)/50 K 10 guns mounted in casemates amidships. Eighteen 70-millimetre (3 in)/50 K 10 guns were mounted on open pivots on the upper deck above the casemates. Three more 66-mm K 10 guns were mounted on the upper turrets for anti-aircraft duties. Four 530-millimetre (21 in) submerged torpedo tubes were fitted, one each in the bow, stern and on each broadside; twelve torpedoes were carried.
The waterline armour belt of the Tegetthoff-class measured 280 millimetres (11 in) thick between the midpoints of the fore and aft barbettes and thinned to 150 millimetres (5.9 in) further towards the bow and stern, but did not reach either the bow or the stern. It was continued to the bow by a small patch of 110–130-millimetre (4–5 in) armour. The upper armour belt had a maximum thickness of 180 millimetres (7.1 in), but it thinned to 110 millimetres (4.3 in) from the forward barbette all the way to the bow. The casemate armour was also 180 millimetres (7.1 in) thick. The sides of the main gun turrets, barbettes and main conning tower were protected by 280 millimetres (11 in) of armour, except for the turret and conning tower roofs which were 60 to 150 millimetres (2 to 6 in) thick. The thickness of the decks ranged from 30 to 48 millimetres (1 to 2 in) in two layers. The underwater protection system consisted of the extension of the double bottom up to the lower edge of the waterline armour belt, with a thin 10-millimetre (0.4 in) plate acting as the outermost bulkhead. It was backed by a torpedo bulkhead that consisted of two layered 25-millimetre plates. The total thickness of this system was only 1.6 metres (5 ft 3 in) which made it incapable of containing a torpedo warhead detonation or mine explosion without rupturing.
Szent István, built at Fiume, differed from her half-sisters mainly in her machinery. She only had two shafts and two turbines, unlike the four shaft arrangement of the other ships of her class. External differences included a platform built around the fore funnel which extended from the bridge to the after funnel and on which several searchlights were installed. A further distinguishing feature was the modified ventilator trunk in front of the mainmast. She was the only ship of her class not to be fitted with torpedo nets.
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