A cruiser is a type of warship. Modern cruisers are generally the largest ships in a fleet after aircraft carriers and amphibious assault ships, and can usually perform several roles.
The term "cruiser", which has been in use for several hundred years, has changed its meaning over time. During the Age of Sail, the term cruising referred to certain kinds of missions—independent scouting, commerce protection, or raiding—fulfilled by frigates or sloops-of-war, which functioned as the cruising warships of a fleet.
In the middle of the 19th century, cruiser came to be a classification of the ships intended for cruising distant waters, for commerce raiding, and for scouting for the battle fleet. Cruisers came in a wide variety of sizes, from the medium-sized protected cruiser to large armored cruisers that were nearly as big (although not as powerful or as well-armored) as a pre-dreadnought battleship. With the advent of the dreadnought battleship before World War I, the armored cruiser evolved into a vessel of similar scale known as the battlecruiser. The very large battlecruisers of the World War I era that succeeded armored cruisers were now classified, along with dreadnought battleships, as capital ships.
By the early 20th century, after World War I, the direct successors to protected 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 these cruisers, which were defined as warships of up to 10,000 tons displacement carrying guns no larger than 8 inches in calibre; whilst the 1930 London Naval Treaty created a divide of two cruiser types, heavy cruisers having 6.1 inches to 8 inch guns, while those with guns of 6.1 inches or less were light cruisers. Each type were limited in total and individual tonnage which shaped cruiser design until the collapse of the treaty system just prior to the start of World War II.