In naval warfare, the line of battle is a tactic in which the ships of the fleet form a line end to end. Its first use is disputed, but variously claimed for dates ranging from 1502 to 1652, with line-of-battle tactics being in wide use by 1675.
The line of battle has the advantage over previous naval tactics—in which ships closed on each other for individual combat—that each ship in the line can fire its broadside without fear of hitting a friendly ship. Therefore in any given amount of time more shots can be fired by the entire fleet.
Another advantage is that a relative movement of the line in relation to some part of the enemy fleet allows for a systematic concentration of fire on that part. To fend off this possibility the other fleet too can move in a line, with the result so typical for sea battle since 1675: two fleets sailing along each other or in opposite tack. A ship powerful enough to stand in the line of battle came to be known as a Ship of the Line (of battle) or a "line of battle" ship which shortened to become "battleship".
It is usually recommended that when forming a line of battle, the heaviest ship with the most armour goes in the front, considering that it will be the one most fired on. It is also best for this ship to have bow chasers. The ship at the back must also have a fair amount of armour, and should carry stern chasers. It is possible to stop the line if necessary, for purposes of firing at coming ships broadside after broadside. It is recommended that the line is broken if it is being constantly raked.