For centuries, half a war fleet might be borrowed merchant ships
Until the seventeenth century, navies routinely pressed trading vessels into service, and more than half a fleet could be merchant ships, because a cargo carrier and a fighting ship were built much alike. Only later did warships diverge into specialised, armoured designs that no cargo hull could imitate.
A warship is built for combat: armed, designed to absorb damage, and usually quicker and nimbler than a merchant vessel, carrying weapons, ammunition and crew supplies rather than cargo. Most belong to national navies, though individuals, cooperatives and companies have operated them too. The boundary has always blurred in wartime. Big merchant ships such as galleons carried guns until piracy faded in the nineteenth century, and in the twentieth century armed merchantmen served as auxiliaries, from the disguised Q-ships of World War I to the armed merchant cruisers of World War II. Warships in turn have hauled troops and supplies, as the eighteenth-century French Navy and the Imperial Japanese Navy did.
The battleship era shows how quickly designs evolved. Ironclads appeared from the late 1850s, followed by pre-dreadnoughts with mixed batteries of guns in several calibres. The dreadnought of the early twentieth century switched to all big guns of one type, so a single firing calculation could aim every turret. Battlecruisers traded armour for battleship-grade guns and higher speed. Seaplane tenders, which carried and serviced seaplanes, are regarded by some as the first aircraft carriers.
Capital ships, once battleships and battlecruisers, now mean aircraft carriers, since the other two types have vanished. Modern surface fleets run from carriers down through amphibious assault ships, cruisers, destroyers, frigates and corvettes to fast attack boats. Cruisers were traditionally the smallest warships able to act independently, yet by 2024 only the United States and Russia still operated ships formally classed that way.
Beneath the surface, midget submarines under 150 tons may carry just one or two crew, while modern boats can stay down for months, limited mainly by food.
Source: Warship
