Category of warship intended for independent long-range operations and scouting purposes but not powerful enough to stand in the line of battle; the steam age successor to the sailing frigate. Its prime characteristics are/were (a) enough speed to get away from anything bigger and (b) enough range to get to interesting places unaided; guns and armour were secondary. They were leading players in the imperial powers' gunboat diplomacy of the era.

In the pre-Dreadnought period (up to 1906) two classes of cruiser developed: light cruisers, usually carrying guns up to 6.1 inch/155 cm calibre but really intended to get out of trouble at the earliest opportunity, and armoured cruisers, slower but more capable of looking after themselves, carrying guns up to 9.4 inch/240 mm calibre. The latter proved to be an unsatisfactory and vulnerable compromise, particularly when battleship speeds became faster with the use of steam turbine engines after 1906 and the battlecruiser class was developed with battleship guns and cruiser speeds; during the first world war light cruisers of increasing size were the only ones built.

In the inter-war period the naval treaties between the great powers signed in London and Washington limited individual cruiser sizes to 10 000 tons displacement with a maximum of 8 inch guns for a new heavy cruiser class and 6.1" guns for light cruisers, and many designs were built to these limits (although both German and Japanese designs secretly exceeded the maximum size). Limits on total heavy cruiser numbers led to a number of ships being built as light cruisers but designed for rapid conversion to carry larger guns in time of war.

During the second world war cruisers served in most theatres of operations on a wide range of duties. The German heavy cruisers (Prinz Eugen, Admiral Hipper)saw service as commerce raiders, while British and American vessels were used for fast troop transport, scouting and patrol missions and widely as convoy escorts where surface and air attack was considered likely (they generally had little to offer against submarines, however); new British (Dido) and US (Atlanta) classes were designed with smaller dual-purpose armaments to improve anti-aircraft capability for use on convoys and in carrier operations.

After the second world war the importance of gun-armed warships diminished rapidly, while the global presence role was taken over by the nuclear submarine; there was little room for relatively big, expensive and vulnerable surface vessels with large crews, so most were scrapped or sold off to third-world navies, although the largest vessels in the missile-armed destroyer and frigate categories were getting up towards the size of cruisers of earlier generations. Both the US and Soviet navies did nonetheless build a number of guided missile cruisers to operate with carrier task forces.

US Navy pennant number prefixes (often used as shorthand for the vessel types):

  • CA - heavy cruiser, armoured cruiser
  • CL - light cruiser
  • CLAA - light anti-aircraft cruiser
  • CLG - light guided missile cruiser
A few notable preserved cruisers of earlier eras which can be visited:
  • Giorgios Averoff (1906) former Greek Navy flagship and the last surviving Armoured cruiser - Palio Faliron, Greece
  • Avrora (1903) light cruiser - a veteran of the disatrous Tsushima expedition - whose shelling of the Winter Palace (with blanks) marked the beginning of the October revolution, Saint Petersburg, Russia.
  • HMS Belfast (1939) - large light cruiser which say heavy action in World War II, London, UK
  • USS Olympia (1895) - protected cruiser, Admiral Dewey's flagship at the Battle of Manila Bay - Pitt's Landing, Philadelphia, USA
  • USS Salem (1949) - the last generation of heavy cruisers, pretty much obsolete when completed; the only surviving 8" gun heavy cruiser in the world - Quincy, MA, USA
  • USS Little Rock (1945) - guided missile cruiser, converted from a World War II light cruiser, former flagship of 2nd and 6th fleets - Buffalo, NY, USA