Heavy cruiser

HMS Frobisher, a Hawkins-class cruiser around which the Washington Naval Treaty limits for heavy cruisers were written.

The heavy cruiser was a type of cruiser, a naval warship designed for long range, high speed and an armament of naval guns roughly 203mm calibre (8 inches). 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.

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Evolution and definition

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, and they were hard to distinguish from a small pre-dreadnought battleship. The lighter, cheaper and faster Second and Third Class cruisers tended to have only an armoured deck and protective coal bunkers, rather than armoured hulls, and hence were known as protected cruisers.

In the first decade of the 20th century, the First Class Armoured Cruiser metamorphosed into the battlecruiser, and increased markedly in size and cost. At the same time, the Third Class Cruiser started to carry thin steel armour on the outside of its hull and became known as the light cruiser. The wide gap between the massive battlecruiser of perhaps 20,000 tons and 305 mm (12-inch) guns and the small light cruiser of up to 5,000 tons and 100 mm (4-in) or 155 mm (6-inch) guns naturally left room for an intermediate type.

The first such design was the British 'Atlantic cruiser' proposal of 1912, which proposed a long-range cruiser of about 8,000 tons displacement with 190 mm (7.5-inch) guns. This was a response to a rumour that Germany was building cruisers to attack merchant shipping in the Atlantic with 170mm guns. The German raiders proved to be fictional and the 'Atlantic cruisers' were never built. However, in 1915 the requirement for long-range trade-protection cruisers resurfaced and resulted in the Hawkins class. Essentially enlarged light cruisers, the Hawkins class each carried seven 190 mm (7.5-inch) guns, and had a displacement just under 10,000 tons.

The old armoured cruiser was not a close ancestor of these heavy cruiser models, even though the name sometimes suggests this. By 1905 the armoured cruiser had grown in size and power to be very close to the pre-dreadnought battleships of the day, with a displacement of around 15,000 tons: considerably larger than the 10,000 tons of the heavy cruiser. This trend resulted in the battlecruiser, which was initially conceived as an armoured cruiser on the same scale as the dreadnought battleship. By 1915, both battleships and battlecruisers had grown markedly; HMS Hood, for instance, designed at around that time, displaced 45,000 tons. The great gap between heavy cruisers and the capital ships of the same generation meant that, unlike the armoured cruiser, the heavy cruiser could not be expected to serve as a junior battleship.

There were also important technical differences between the heavy cruiser and the armoured cruiser, some of which reflected the generational gap between them. Heavy cruisers, like all contemporary ships, were typically powered by oil-fired steam turbine engines and were capable of far faster speeds than armoured cruisers had ever been (propelled by coal-fired reciprocating steam engines of their era). Like their protected cruiser predecessors and contemporary light cruisers, heavy cruisers lacked a side armoured belt, saving weight to achieve high speeds. The main armament of a heavy cruiser at a maximum 203 mm (8-inch) was smaller than the typical 233 mm (9.2-inch) guns of later armoured cruisers. Nonetheless, heavy cruisers often had a larger number of main guns (some armoured cruisers had a mixed instead of uniform complement of main guns), discarded the mounting of main guns in casemates in favor of center-line superfiring turrets (saved tonnage and enabled the ship to fire all guns on one broadside), and benefited from the introduction of fire control in the 1920s and 30s, meaning that the heavy cruiser was considerably more powerful.

Washington Treaty

HMAS Canberra, a County-class "treaty cruiser".

The Washington Naval Treaty of 1922 introduced very strict limits on the construction of battleships and battlecruisers, defined as warships of more than 10,000 tons standard displacement or with armament of a calibre greater than eight inches (203 mm). Under this limit, far fewer restrictions applied. The 10,000 tons and 203 mm (8-inch) level was set with reference to the British Hawkins class, but both Japan and the USA were also considering designs on a similar specification. The Japanese model became the Furutaka class.

The emergence of these new, powerful cruiser classes sparked off something of a cruiser arms-race. The Japanese navy had a doctrine of building more powerful ships in every class than its likely opponents, which led to the development of several very impressive heavy cruiser classes. British and American building was more influenced by the desire to be able to match the Japanese ships while keeping enough cruisers for their other global responsibilities. With battleships heavily regulated by the Washington Treaty, and aircraft carriers not yet mature, the cruiser question became the focus of naval affairs. The British, with a strained economy and global commitments, favoured unlimited cruiser tonnage but strict limits on the individual ships. The Americans favoured the opposite: strictly limited numbers of powerful cruisers. Disagreements between the British and Americans wrecked the 1927 conference on naval affairs.

Even during the 1920s, the 10,000 ton limit was not strictly observed. British, French and American designers generally worked to the limit with precision. The Japanese Myoko class, however, grew during its construction as the naval general staff prevailed on the designers to increase the weapons load. As well as a breach of the Treaty, this was a poor decision from the design point of view and the ships had to be reconstructed in the 1930s to reduce weight. The German Deutschland class, was classified as armoured coast defence ships under the terms of the Treaty of Versailles. They superficially resembled contemporary battleships due to their massive main gun turrets and unusually high conning tower/bridge. However, they were in effect a heavy cruiser being upgunned to 11-inch batteries at the cost of slower speed; their displacement was declared at 10,000 tons but was in practice considerably greater.

The Pensacola class cruisers were the US Navy's first "treaty cruisers", adhering to the Washington Naval Treaty restrictions. Their main battery consisted of the maximum 8" guns permitted by the treaty. However, they had a thin armor deck (varying from 2.5 to 4 inches in thickness), no thicker than the armor on 6" gun cruisers, being inadequate to protect their vitals from enemy 8" shells. The two vessels in this class, Pensacola and Salt Lake City, were originally classified as light cruisers due to their minimal armor until re-designated in July 1931 as heavy cruisers in accord with international practice of designating all cruisers with guns larger than 6".

London Treaty

In 1930 the Washington Naval Treaty was extended by the London Naval Treaty, which finally settled the arguments on cruisers which had raged in the 1920s. The treaty defined limits on both heavy cruisers - those with guns larger than 155 mm (6.1 inches) - and light cruisers - those with smaller-calibre guns. The limit of 10,000 tons displacement still applied to both. This was the point at which the split between 'heavy' and 'light' cruisers finally became official and widespread.

The Treaty satisfied Britain and America. However, it deeply offended Japan, as this severely limited the numbers of heavy cruisers that the Imperial Japanese Navy could have, as they considered heavy cruisers as key warships in a line of battle with their 8-inch guns and heavy torpedo armament. The IJN placed less priority on purpose-built light cruisers, most of their existing types dating back to the 1920s (the five WWII-era light cruisers that the IJN commissioned were less well-armed than light cruisers of the US and Royal Navies), which were largely relegated to leading destroyer squadrons. The solution the Japanese adopted was to build the Mogami class, which was declared as a 10,000 ton light cruiser with fifteen 6.1-inch guns. In practice, they displaced over 12,000 tons, and it was always intended to replace her turrets to give a final armament of ten 203 mm guns, making something of a nonsense of the light and heavy cruiser classifications.

The German navy also paid lip-service to the treaty limitations, with the Admiral Hipper class weighing in at 14,000 tons.

In the mid 1930s, Britain, France and Italy ceased building heavy cruisers. It was felt that in a likely cruiser engagement, a larger number of 155 mm (6-inch) guns would be preferable to a smaller number of 203 mm (8-inch). The heavier shell of the 203 mm weapon was of little advantage, as most ships that could withstand a 6-inch hit were also well-protected against eight-inch shells. This led to the construction of cruisers up to the 10,000-tons limit, with twelve to fifteen 155 mm guns. While these ships fell into the 'light cruiser' classification by virtue of the calibre of their main armament, they were designed to fight a heavy cruiser on equal terms, again making something of a nonsense of the classifications.

The 1936 London Naval Treaty, principally negotiated between Britain and the United States but never ratified, abolished the heavy cruiser entirely by restricting new construction to 8,000 tons and 155 mm (6.1-inch) guns. This suited Britain's needs very well, but was largely a dead letter. The U.S. continued to build heavy cruisers, culminating in the New Orleans class and USS Wichita.

Second World War

IJN Maya a Takao class heavy cruiser.

Heavy cruisers were still being built, and they could be balanced designs when nations decided to skirt the restrictions imposed by the London Naval Treaty.

The Germans built their Hipper class heavy cruisers of 14,000 tons, although the Anglo-German Naval Agreement was supposed to limit their shipbuilding.

The U.S. built the Baltimore class of heavy cruisers during the war. While earlier heavy cruisers were noted for their powerful torpedo armament (especially Japanese heavy cruisers), later ships built by the USN concentrated mainly on anti-aircraft armament as their main role was escorting aircraft carriers instead of engaging in surface actions. Interestingly, most Japanese heavy cruisers were sunk by aircraft or submarines, instead of during surface engagements.[1]

Example of heavy cruiser evolution during the Second World War: Duquesne in original anti-surface layout

Tourville after refit: reinforced anti-air armament, removal of sea plane, torpedo launchers and aft mast

The U.S. built the last heavy cruisers, which were finished shortly after the war. The Baltimore class consisted of seventeen ships, including six of the slightly different Oregon City class. The Des Moines class were the last heavy cruisers built, though based on the Baltimores, they were considerably heavier due to their new rapid-firing 203 mm (8-inch) guns. Additionally, two aircraft carriers were built on a Baltimore-derived hull, the Saipan class.

The largest heavy cruisers were the Alaska class of "large cruiser". Though they resembled contemporary battlecruisers or battleships in general appearance, as well as having main armament and displacement equal or greater than that of capital ships of the First World War, they were actually upscaled heavy cruisers. The Alaskas, for instance, lacked the armoured belt and torpedo defense system of true capital ships. They also had proportionately less weight in armour at 16% of displacement, similar to heavy cruisers, in contrast to the British battlecruiser Hood of 30%, and the German Scharnhorst and US North Carolina battleships of 40%. The layout of the Alaskas machinery and the possession of a single rudder was also based on that of cruisers rather than that of capital ships.

USS Columbus in 1965. Originally a Baltimore class cruiser, she was rebuilt into an Albany class guided missile cruiser.

Heavy cruisers fell out of use after the Second World War. Some existing US heavy cruisers lasted until the 1970s, sometimes after conversion to guided missile cruisers (US hull symbol CG).

The last heavy cruiser in existence (as of 2006) is the USS Salem, now a museum ship.

References

  1. ↑ JUNYOKAN! Stories and Battle Histories of the IJN's Cruiser Force

See also