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 armored 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 battlecruisers
with heavy anti-ship missiles designed to sink NATO carrier task forces.