A cruiser is a type of warship. The term has been in use for several hundred years, and has had different meanings throughout this period. During the Age of Sail, the term cruising referred to certain kinds of missions – independent scouting, raiding or commerce protection – fulfilled by a frigate or sloop, which were the cruising warships of a fleet.
From the middle of the 19th century, cruiser came to be a classification for the ships intended for this kind of role, though cruisers came in a wide variety of sizes, from the small protected cruiser to armoured cruisers which were as large (though not as powerful) as a battleship.
By the early 20th century, cruisers could be placed on a consistent scale of warship size, smaller than a battleship but larger than a destroyer. In 1922, the Washington Naval Treaty placed a formal limit on cruisers, which were defined as warships of up to 10,000 tons displacement carrying guns no larger than 8 inches in calibre. These limits shaped cruisers up until the end of World War II. The very large battlecruisers of the World War I era were now classified, along with battleships, as capital ships.
In the later 20th century, the obsolescence of the battleship left the cruiser as the largest and most powerful surface combatant. The role of the cruiser varied according to ship and navy, often including air defense, commerce raiding and shore bombardment. The U.S. Navy in the Cold War period built guided-missile cruisers primarily designed to provide air defense, while the navy of the USSR built cruisers with heavy anti-ship missiles designed to sink NATO carrier task forces.
Currently only three nations, the United States, Russia, and Peru (BAP Almirante Grau (CLM-81) while still in service with the Peruvian Navy), operate cruisers, though the line between cruisers and destroyers is once again blurred. New models of destroyers (for instance the Zumwalt class) are often larger and more powerful than cruiser classes they replace.
Read more about Cruiser: Early History, Steam Cruisers, Steel Cruisers, Cruisers From 1900 To 1914, World War I, Cruisers From 1919-1945, Later 20th Century, Cruisers in Service Today, The US Navy's "cruiser Gap"