The heavy cruiser was a type of cruiser, a naval warship designed for long range and high speed, armed generally with naval guns of roughly 203 mm (8 inches) in calibre, whose design parameters were dictated by the Washington Naval Treaty of 1922 and the London Naval Treaty of 1930. The heavy cruiser is part of a lineage of ship design from 1915 through the early 1950s, although the term "heavy cruiser" only came into formal use in 1930. The heavy cruiser's immediate precursors were the light cruiser designs of the 1900s and 1910s, rather than the armoured cruisers of the years before 1905. When the armoured cruiser was supplanted by the battlecruiser, an intermediate ship type between this and the light cruiser was found to be needed—one larger and more powerful than the light cruisers of a potential enemy but not as large and expensive as the battlecruiser so as to be built in sufficient numbers to protect merchant ships and serve in a number of combat theatres.
With their intended targets being other cruisers and smaller vessels, the role of the heavy cruiser differed fundamentally from that of the armoured cruiser. Also, the heavy cruiser was designed to take advantage of advances in naval technology and design. Typically powered by oil-fired steam turbines rather than the reciprocating steam engines of the armoured cruiser, heavy cruisers were capable of far faster speeds and could cruise at high speed for much longer than could an armoured cruiser. They used uniform main guns, mounted in centre-line superfiring turrets rather than casemates. Casemate guns and a mixed battery were eliminated to make room for above deck torpedoes, and ever increasing and more effective anti-aircraft armaments. They also benefited from the superior fire control of the 1920s and continually upgraded through the 1950s. Late in the development cycle radar and electronic countermeasures would also appear and rapidly gain in importance.
History
Development
At the end of the 19th century, cruisers were classified as first, second or third class depending on their capabilities. First-class cruisers were typically armoured cruisers, with belt side armour, while lighter, cheaper and faster second- and third-class cruisers tended to have only an armoured deck and protective coal bunkers, rather than armoured hulls; they were hence known as protected cruisers. Their essential role had not changed since the age of sail—to serve on long-range missions, patrol for enemy warships and raid and defend commerce. Armoured cruisers had proved less versatile than needed to do this adequately. In a race to outsize and outgun one another, they had grown to around 15,000 tons and up to in main gun calibre—very close to the pre-dreadnought battleships of the day, although they were generally ascribed to be weaker than the battleship due to their lack of armour and not appreciably faster due to the limits of engine technology at the time. While Japanese armoured cruisers had distinguished themselves at the Battle of Tsushima in 1905, the armoured cruiser as it was then known had reached the pinnacle of its development.
Tactics and technology were gearing towards naval encounters held over increasingly longer ranges, which demanded an armament of primarily large calibre guns. The demand for speed with which to outflank a potential enemy and fulfil its traditional role as scout for the fleet demanded a speed preferably 30 percent faster than battleships. Thirty percent was the ratio by which frigates had been faster than ships of the line in the days of sail. If a battleship sailed at 20 knots, this would mean that an armoured cruiser would have to steam at least 26 or 27 knots.