Heavy cruiser
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The heavy cruiser was a type of cruiser; a naval warship. The first heavy cruisers were built in 1915, although the official definition was not finalised until much later (see below). Both the heavy and light cruiser were descended from the protected cruisers and armoured cruisers of the last part of the 19th Century. The heavy cruiser was generally heavier and armed with larger-calibre guns than the light cruiser.
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[edit] Evolution & definition
[edit] Washington Treaty
The Washington Naval Treaty of 1921 restricted the construction of warships of more than 10,000 tons standard displacement or with armament of a calibre greater than eight inches (203 mm). These limits were defined by the existence of the British Royal Navy's 9,750 ton, 7.5-inch (190 mm) gun Hawkins class of 1915. These ships were directly descended from the preceding Birmingham group of Town class 5,440 ton light cruisers and at the time were referred to as "improved light cruisers". The major naval powers began building cruisers up to these limits.
[edit] London Treaty
In 1930 the Washington Naval Treaty was extended by the London Naval Treaty, which split the treaty definition of a cruiser into heavy cruisers - those with guns larger than 6.1 inches (155 mm) - and light cruisers - those with smaller-caliber guns. The upper limit of 10,000 tons displacement still applied to both. This treaty finalised the definition of these warship types.
By the mid 1930s, Britain, France and Italy had ceased building heavy cruisers, to concentrate on light cruiser construction that they judged more suited to their needs. Armament based on eight-inch (203 mm) guns was considered overall to be inferior to that using six-inch (152 mm) guns, which could be fired faster and weighed less than the eight inch. The heavier shell of the eight inch was of little advantage, as most ships that could withstand a six inch (152 mm) hit were also well-protected against eight-inch shells. This led to the construction of large light cruisers up to the 10,000-tons limit, with twelve to fifteen six-inch guns.
[edit] In the United States Navy
In the United States Navy, the term first came into official use in 1930, with the hull classification symbol CA which it took over from the Armoured cruiser. Earlier heavy cruisers had been given the CL designation (for light cruisers), and were then reclassified.
The London Naval Treaty of 1930 essentially abolished the term armoured cruiser, and adopted the terms heavy cruiser and light cruiser. After this, the symbol "CA" was used to designate 'heavy cruiser'. Though heavy cruisers often had similar gun calibres to armoured cruisers, heavy cruisers owed far more of their design lineage to light cruisers.
[edit] Post Treaty and WWII
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.
In the 1930s several navies began to secretly flout the tonnage limits. The Japanese who were planning on withdrawing from the treaty built the Mogami class with a displacement of over 12,000 tons. She was designed so that her five 6.1-inch gun triple turrets could be replaced with twin 8-inch gun turrets and the ships of the class were rearmed in that way shortly before World War II. Japan withdrew from the Washington Naval Treaty in 1936, after which there was no effective regulation.
The United States built heavy cruisers up to World War II, culminating in the heavily armored New Orleans class and USS Wichita, and continued building the larger Baltimore class during the war. The Germans built their Hipper class heavy cruisers of 14,000 tons, although the Anglo-German Naval Agreement was supposed to limit their shipbuilding. 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.
The United States 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 8-inch guns. Additionally, two aircraft carriers were built on a Baltimore-derived hull, the Saipan class (CVL-48 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 World War I capital ships, 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.
[edit] Post-WWII
Heavy cruisers fell out of use after World War II. Some existing US heavy cruisers lasted until the 1970s, sometimes after conversion to guided missile cruisers (US hull symbol CG).
With the development of guided missile cruisers in the 1950s, the designation system changed to designate cruisers by their primary armament. Primarily gun-armed cruisers were designated "gun cruisers" (hull classification symbol CA) while primarily missile-armed cruisers were designated "guided missile cruisers" (hull classification symbol CG).
The last heavy cruiser in existence (as of 2006) is the USS Salem, now a museum ship.
