Heavy cruisers

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 203mm calibre (8 inches in caliber) and displacing approximately 10,000 tons. While the general mission of the heavy cruiser, to act as a fast scout for a battle fleet and protect and hunt down commerce, was largely unchanged from the days of sail, its design parameters were dictated by the Washington Naval Treaty of 1922 and the London Naval Treaty of 1930.

The heavy cruiser can be seen as a lineage of ship design from 1915 until 1945, 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 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 theaters.

With their intended targets being other cruisers and smaller vessels, the role of the heavy cruiser differed fundamentally from that of the armored 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 much longer time than could an armoured cruiser. They often had a larger number of main guns than did armoured cruisers, mounted in center-line superfiring turrets rather than casemates. This arrangement saved tonnage and enabled the ship to fire all guns on one broadside. They also benefited from the introduction of fire control in the 1920s and 1930s. These developments meant that the heavy cruiser was an overall more powerful ship type than the armoured cruiser had been.

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 armor, 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 9.2 and 10 inches (230 and 250 mm) in main gun caliber—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 armor and not appreciably faster due to the limits of engine technology at the time. While Japanese armored cruisers had distinguished themselves at the Battle of Tsushima in 1905, the armoured cruiser as it was then known had reached the end of its development.

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