The word battleship is shorthand for 'ship of the line of battle'
Twentieth-century battleships got their name from a sailing-era tactic. Fleets in the 17th century began forming single-file lines to trade broadsides, and only the strongest ships, those fit to stand in the line, were called ships of the line. Germany kept calling its battleships line ships until World War I.
The line of battle emerged in the early to mid-17th century, led by the Dutch and English navies. Earlier fleets simply closed in and fought in whatever order they found themselves, boarding when they could. Once coordinated cannon fire from one side of a ship dominated, ships sailed in file on the same tack as the enemy, hammering away until one side retreated. A weak link could break the line, so only vessels with comparably strong sides were allowed in, while lighter craft scouted and relayed signals the flagship could not see.
The ancestor was the armed carrack, developed in Portugal and adopted across Europe by the early 16th century, blending the North Sea cog with the Mediterranean galley. Its towering castles at bow and stern let archers shoot down on enemies. England's Mary Rose, built at Portsmouth from 1510 to 1512, mounted 91 guns after a 1530s refit but sank by accident at the Battle of the Solent in 1545. The larger Henri Grâce à Dieu, or Great Harry, was among the first ships with gunports and a true broadside, and at launch was Europe's mightiest warship, though she served mostly for show, sometimes under gold cloth sails.
As gunfire replaced boarding, tall forecastles became a liability, pushing the bow down when running before the wind. The sleeker galleon evolved from the carrack in the 16th century and dominated the English and Spanish fleets at Gravelines in 1588. By the 1637 launch of England's Sovereign of the Seas, the forecastle had vanished, and line tactics shrank the castles further, freeing hulls to grow and carry more guns.
Galleys faded, becoming largely useless in naval battles by around 1750. From the late 1840s steam brought screw-driven wooden ships of the line, but the ironclad frigate, from 1859, made them obsolete.
Source: Ship of the line
