The English warship Mary Rose
, one of the earliest warships with a broadside armament; illustration from the Anthony Roll
, c. 1546
Since ancient times, war at sea had been fought much like on land: with melee weapons and bows and arrows, but on floating wooden platforms rather than battlefields. Though the introduction of guns was a significant change, it only slowly changed the dynamics of ship-to-ship combat. The first guns on ships were small wrought-iron pieces mounted on the open decks and in the fighting tops, often requiring only one or two men to handle them. They were designed to injure, kill or simply stun, shock and frighten the enemy prior to boarding. As guns were made more durable to withstand stronger gunpowder charges, they increased their potential to inflict critical damage to the vessel rather than just its crew. Since these guns were much heavier than the earlier anti-personnel weapons, they had to be placed lower in the ships, and fire from gunports, to avoid ships becoming unstable. In Northern Europe the technique of building ships with clinker planking made it difficult to cut ports in the hull; clinker-built (or clench-built) ships had much of their structural strength in the outer hull. The solution was the gradual adoption of carvel-built ships that relied on an internal skeleton structure to bear the weight of the ship. The development of propulsion during the 15th century from single-masted, square-rigged cogs to three-masted carracks with a mix of square and lateen sails made ships nimbler and easier to maneuver.
Gunports cut in the hull of ships had been common practise as early as 1501. According to tradition the inventor was a Breton shipwright called Descharges, but it is just as likely to have been a gradual adaptation of loading ports in the stern of merchant vessels that had already been in use for centuries. Initially, the gunports were used to mount heavy so-called stern chasers pointing aft, but soon gun ports migrated to the sides of ships. This made possible coordinated volleys from all the guns on one side of a ship for the first time in history, at least in theory. Guns in the 16th century were considered to be in fixed positions and were intended to be fired independently rather than in concerted volleys. It was not until the 1590s that the word "broadside" in English was commonly used to refer to gunfire from the side of a ship rather than the ship's side itself.
firing her guns broadside (1984). Note that intervening structures such as the bridge tower would prevent all of the guns from being focused directly forward or aft.
The main batteries in 20th century battleships tended to be powered gun turrets which could swivel 180 degrees or more to establish wider firing arcs around the entire vessel. Although this could allow at least some of the main guns to be focused directly forward or aft, most or all battleships still relied on broadsides for maximum firepower. Structures such as the bridge tower in the middle of a battleship would prevent guns in the aft portion of the ship from firing forward, and vice versa. Additionally, directing the guns to the port or starboard projected the massive muzzle blast out over the ocean, while firing the guns too close to the deck could cause damage to the ship.