In naval warfare, the line of battle is a tactic in which the ships of the fleet form a line, end-to-end. Its origins are traditionally ascribed to the navy of the Commonwealth of England, especially to General at Sea Robert Blake who wrote the Sailing and Fighting Instructions of 1653. However, it was already used by the Portuguese under Vasco Da Gama in 1502 near Malabar against a Muslim fleet, and for the first time in European waters in the Action of 18 September 1639 by Dutch Lieutenant-Admiral Maarten Tromp.
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". The line is at its most effective when moving perpendicular to the axis of movement of the enemy fleet, e.g. by "crossing the T" or by breaking the enemy line and moving through it (e.g. Four Days Battle, Battle of Schooneveld, Battle of Trafalgar), by trying to cut off and isolate part of the enemy's line and concentrating a stronger force on it (e.g. Battle of Texel, Battle of the Saintes), or by trying to 'double up' the enemy's ships (e.g. Battle of Beachy Head). This way the enemy ships block each other's line of fire.
From the mid 16th century the cannon gradually became the most important weapon in naval warfare, replacing boarding actions as the decisive factor in combat. At the same time, the natural tendency in the design of galleons was for longer ships with lower castles, which meant faster, more stable vessels. These newer warships could mount more cannon along the sides of their decks, concentrating their firepower along their broadside.
Until the mid 17th Century, the tactics of a fleet were often to 'charge' the enemy, firing bow chaser cannon, which did not deploy the broadside to its best effect. These new vessels required new tactics, and "since.. almost all the artillery is found upon the sides of a ship of war, hence it is the beam that must necessarily and always be turned toward the enemy. On the other hand, it is necessary that the sight of the latter must never be interrupted by a friendly ship. Only one formation allows the ships of the same fleet to satisfy fully these conditions. That formation is the line ahead [column]. This line, therefore, is imposed as the only order of battle, and consequently as the basis of all fleet tactics.
Modern research has shown that the first documented deliberate use seems to be in the Action of 18 September 1639 by Dutch Lieutenant-Admiral Maarten Tromp who employed it to damage a Spanish fleet, far superior in numbers and firepower, so severely it took refuge in The Downs where he would destroy it five weeks later in the Battle of the Downs. The United Provinces, however, did not formalise it into an official doctrine. Even before the Dutch, the Portuguese had already made it standard practice to assume a line-ahead formation. It was used as early as 1502 under Vasco Da Gama against a large Muslim fleet off Malabar, and in 1557 when the English pirate William Towerson was routed by repeated broadsides from a Portuguese squadron in a line-ahead formation.
In the 1652 battles of the First Anglo-Dutch War the Dutch again used the line-of-battle when trying to defend themselves against the heavier English vessels. On 29 March 1653, the English issued the 'Instructions for the better ordering of the Fleet in Fighting', instructing each of the three squadrons of their fleet to 'keep in line with their chief' and ships out of station to return to the 'wake or grain' of their flagship.
The next major battle of the war, the Battle of the Gabbard, was a decisive English victory and caused severe losses to the Dutch fleet.
After this war the English perfected the method; but the Dutch were slower to adopt the modern tactic, still having no written instructions when the Second Anglo-Dutch War broke out. An attempt to employ the line-of-battle against the English by Dutch Lieutenant-Admiral Jacob van Wassenaer Obdam failed catastrophically in the Battle of Lowestoft due to insufficient training and confusion among the lower ranks whether the line should be used or the direct attack. In the summer of 1665 the Dutch too wrote formal instructions. Michiel de Ruyter used the line-of-battle with great ability in the Four Days Battle. That the English were still more competent in it was shown in the St. James's Day Battle when they recovered much earlier from exceptional weather conditions causing large manpower losses to the Dutch.
During the later 17th Century the British became rather dogmatic about the line-of-battle, trying to employ it even in unfavourable conditions, as shown in the Battle of Beachy Head and the Battles of Barfleur and La Hougue, where the French gained an advantage because of British inflexibility. This worsened during the 18th century when the line-of-battle became a dogmatic doctrine; in 1778, at the First Battle of Ushant, the French escaped, in part due to British over-reliance on the line. Nevertheless, the lateness of the British fleet in forming the line became the pretext for the politically-motivated court-martials of Admirals Keppel and Palliser.
After further reverses in the American Revolutionary Wars, where British lines proved vulnerable to faster French warships using hit-and-run tactics, the Royal Navy became receptive to new ideas about the line tactic. John Clerk, an Edinburgh merchant, published a book called 'An Essay on Naval Tactics', emphasising the need to concentrate fire on a part of the enemy's line of battle. The book circulated widely, including to naval officers.
At the Battle of the Saints in 1782 a British fleet under Admiral Rodney broke across the enemy line instead of keeping their own line intact at all costs. Whether this was deliberate, or indeed desirable, was and still is disputed. The result was nevertheless hailed as the greatest victory since the Seven Years War. The Battle of the First of June (1794) saw a return to the mêlée. British admirals, Nelson amongst them, continued to develop offensive modifications to the simple line ahead tactic throughout the Revolutionary and Napoleonic wars.
For a time sea-officers were inclined to doubt whether order could be maintained among vessels subject to the forces of wind and tide. But, in the very first years of the 16th century, the Spanish writer Alonso de Chaves argued that even an approach to order was superior to none, and that, given the accidents of wind and tide, and given that the early means of injuring an enemy at a distance were nil, the advantage would rest with the one who took his precautions. This truth was so obvious that it could not help but be universally accepted. The line ahead then became the "line of battle".
The governing principles were simple and were essentially sound. The ships were arranged in a line, in order that each should have her broadside free to fire into the enemy without running the risk of firing into her own friends. In order to remove the danger that they would collide and allow for a change of course in case of need, a space was left between them. It was fixed at two cables – that is, 200 fathoms, or 400 yards – though less room was occasionally taken.
In a large fleet, the line was typically divided into three squadrons, or divisions, each under a subordinate admiral. Note that, unlike land armies, there is no advanced guard, rear guard, and vanguard (a.k.a. Main Body) because changes in wind direction, sailing direction, and position of the enemy fleet would make this too confusing. Rather, one squadron usually remained under the direct command of the Admiral of the Fleet, one squadron was commanded by a Vice Admiral and one by a Rear Admiral, each of the three squadrons flying different coloured flags. The flag of the Fleet Admiral's squadron is red, the Vice Admiral's is white and the Rear Admiral's blue. Although the names Vice (advanced) and Rear may have derived from sailing positions within the line at the moment of engagement it was more common to refer to squadrons by their colour, or by the name and the admiral's ship and, in conversation but not in signals, by the name of the commander.
To reduce the number of men required to handle the sails, and leave them free to fight the guns, the ships fought under reduced canvas. But it was necessary to retain the power to increase the speed of a ship rapidly. This was secured by not sheeting home one of the sails – that is to say, it was left loose, and the wind was "spilt out of it". When the vessel was required to shoot ahead it was easy to sheet the sail home, and "let all draw". The fleets would fight "on the wind" – that is to say, with the wind on the side, because they were then under better control. With the wind blowing from behind they would take the wind out of one another’s sails. When the course had to be altered, the ships turned by tacking – that is, head to wind – or by wearing – that is, stern to wind, either together or in succession.
To tack or wear a large fleet in succession was a very lengthy operation. The second ship did not tack, or wear, until she had reached the place where the first had turned, and so on, down the whole line. By tacking or wearing together the order of a fleet was reversed, the forward squadron becoming the rear, and the rear the van. It must be remembered that a fleet was divided into squadrons, which kept their names even when the order was reversed. Orders were given by signals from the flagship, but as they could not always be seen by the ships in a line with her, frigates were stationed on the disengaged side of the line to repeat signals.
A main object which the admirals who drafted the British Sailing and Fighting Instructions had before them was to obviate the risk that the enemy would double on one end of the line and put it between two fires. It is obvious that if two fleets, A and B, are sailing, both with the wind on the starboard side, and the leading ship of A comes into action with the seventh or eighth of B, then six or seven leading ships of B’s line will be free to turn and surround the head of A’s line, a tactic known as doubling. This actually happened at the Battle of Beachy Head (1690). Therefore, the orders enjoin on the admiral the strict obligation to come into action in such a way that his leading ship shall steer with the leading ship of the enemy, and his rear with the rear. The familiar expression of the British navy was "to take every man his bird".
The regular method of fighting battles was thus set up. In itself it was founded on sound principles. As it was framed when the enemies kept in view were the Dutch, who in seamanship, strategy and tactics and gunnery were fully equal to the British, its authors were justified in prescribing the safe course. Unhappily they added the direction that a British admiral was to keep his fleet, throughout the battle, in the order in which it was begun. Therefore he could take no advantage of any disorder which might occur in the enemy’s lines.
For a period in the late 19th century, naval tactics became chaotic as ironclad warships were introduced. One school of thought held that ironclads were effectively invulnerable to gunfire, so ramming became a popular method of attack, for instance at the Battle of Lissa or the Battle of the Yalu River. Another held that naval battles would only be decided by an assault on an enemy fleet in port. Ships built according to these doctrines tended to mount a handful of guns which could fire ahead or all-round, rather than broadside. The fleets of these periods tended to use the line of battle less.
However, as ramming fell out of fashion, the logic of the line of battle returned; used in the Battle of Tsushima of 1905, the Battle of Jutland in 1916 and finally in the Battle of Surigao Strait in 1944.
During World War II the development of aircraft carriers and the guided missile meant that gun engagements would never again be decisive. This meant there was no rationale for using a line-of-battle formation. In modern naval warfare, a battlegroup generally deploys with the highest-value units in the centre, accompanied closely by anti-aircraft escorts, with a number of anti-submarine escorts surrounding the formation at a distance of tens of miles.