Central battery ship

The centre battery ship (UK) or casemate ship (continental navies) was a development of the (high-freeboard) broadside ironclad of the 1860s. The central battery ships had their main guns concentrated in the middle of the ship in an armoured citadel. The concentration of armament amidships meant the ship could be shorter and handier than a broadside type like previous warships. In this manner the design could maximize the thickness of armour in a limited area while still carrying a significant broadside. These ships meant the end of the armoured frigates with their full-length gun decks.

In the UK, the man behind the design was the newly appointed Chief Constructor of the Royal Navy, Edward James Reed. The previous Royal Navy ironclad designs, represented by HMS Warrior, had proven to be seaworthy, fast under power and sail, but their armour could be easily penetrated by more modern guns. The first central battery ship was HMS Bellerophon of 1865. Great Britain built a total of 18 central battery ships before turrets became common on high-freeboard ships in the 1880s.

The 2nd British central battery ship, HMS Hercules, served as model for the Austrian navy, starting with their first design SMS Lissa (6,100 tons) designed by Joseph von Romako and launched in 1871. The Austrian SMS Kaiser (1871)—not to be confused with German SMS Kaiser (1874)—was built along a similar design, although the hull had been converted from a wooden ship, and it was slightly smaller (5,800 tons). The Austrian central battery design was pushed further with SMS Custoza (7,100 tons) and SMS Erzherzog Albrecht (5,900 tons), which had double-decked casemates; after studying the Battle of Lissa, Romako designed these so more guns could shoot forward. Three older broadside ironclads of the Kaiser Max class (3600 tons: Kaiser Max, Don Juan D'Austria and Prinz Eugen) were also officially "converted" to casemate design, although they were mostly built from scratch. The largest design yet was the SMS Tegetthoff (1878), later renamed to Mars when SMS Tegetthoff (1912) was commissioned. The Austrian records distinguish between the category of older broadside ironclads and the newer designs using the words Panzerfregatten (armoured frigates) and respectively Casemattschiffe (casemate ships).

The German navy had two large casemate ships (about 8800 tons) of the Kaiser class built in UK shipyards. The first ironclad of the Greek navy, Vasilefs Georgios (1867), was also built in the UK; at 1700 tons, it was a minimalist casemate design having only two large 9in guns, and two small 20 pounders. The Italians had only one casemate ship built, the Venezia, converted from broadside during construction.

The disadvantage of the centre-battery was that, while more flexible than the broadside, each gun still had a relatively restricted field of fire and few guns could fire directly ahead. The centre-battery ships were soon succeeded by turreted warships.