A ship of the line was a type of naval warship constructed during the Age of Sail from the 17th century to the mid-19th century. The ship of the line was designed for the naval tactic known as the line of battle, which involved the two columns of opposing warships maneuvering to volley fire with the cannons along their broadsides. In conflicts where opposing ships were both able to fire from their broadsides, the opponent with more cannons firing – and therefore more firepower – typically had an advantage.

A warship or combatant ship is a ship that is built and primarily intended for naval warfare. Usually they belong to the armed forces of a nation. As well as being armed, warships are designed to withstand damage and are typically faster and more maneuverable than merchant ships. Unlike a merchant ship, which carries cargo, a warship typically carries only weapons, ammunition and supplies for its crew. Warships usually belong to a navy, though they have also been operated by individuals, cooperatives and corporations.