Historically a cruiser was not a type of ship but a warship role. Cruisers were ships—often frigates or smaller vessels—which were assigned a role largely independent from the fleet. Typically this might involve missions such as raiding enemy merchant shipping. In the late 19th century the term 'cruiser' came to mean ships designed to fulfill such a role, and from the 1890s to the 1950s a 'cruiser' was a warship larger than a destroyer but smaller than a battleship. For much of 19th century and the first half of the 20th, the cruiser was a navy's long-range "force projection" weapon, while the larger ships stayed nearer to home. Their main role was to attack enemy merchant vessels, so much so that this task came to be called cruiser warfare. Other roles included reconnaissance, and cruisers were often attached to the battlefleet. In the later 20th century, the decline of the battleship left the cruiser as the largest and most powerful surface combatant. However, the role of the cruiser increasingly became one of providing air defence for a fleet, rather than independent cruiser warfare. At the beginning of the 21st century, cruisers were the heaviest surface combatant ships in use, with only five nations (the United States, Russia, France, Italy and Peru) operating these at the time. Following the Italian Navy's 2003 decommissioning of , only four nations currently operate cruisers.

Early history

The term "cruiser" or "cruizer" was first commonly used in the 17th century to refer to an independent warship. "Cruiser" meant the purpose or mission of a ship, rather than a category of vessel. However, the term was nonetheless used to mean a smaller, faster warship suitable for such a role. In the 17th century, the ship of the line was generally too large, inflexible and expensive to be dispatched on long-range missions (for instance, to the Americas), and too strategically important to be put at risk of fouling and foundering by continual patrol duties. The Dutch navy was noted for its cruisers in the 17th century, while the British and later French and Spanish later caught up in terms of their numbers and deployment. The British Cruiser and Convoy Acts were an attempt by mercantile interests in Parliament to focus the Navy on commerce defence and raiding with cruisers, rather than the more scarce and expensive ships of the line. During the 18th century the frigate became the pre-eminent type of cruiser. A frigate was a small, fast, long range, lightly armed (single gun-deck) ship used for scouting, carrying dispatches, and disrupting enemy trade. The other principal type of cruiser was the sloop, but many other miscellaneous types of ship were used as well.

Steam Cruisers

During the 19th century, as steam propulsion became the norm, fleets started to use the term 'cruiser' more descriptively to refer to some ironclad warships as well as a miscellany of unarmored frigates, sloops, and corvettes, most of which had mixed steam and sail propulsion.