Vertical Line, (ligne verticale, Fr.) a line which is raised perpendicularly above or below the horizon. Of this description are all lines that express height or depth.
The Line. This term is frequently used to distinguish the regular army from other establishments of a military nature. All numbered or marching regiments are called the line. The marines, militia, and volunteers, do not come under the term. It is, however, a corruption of the word, since the true import of line in military matters, means that solid part of an army which is called the main body, and has a regular formation from right to left. Thus in the seven years war, when prince Ferdinand commanded the allied army, the British troops under the marquis of Granby did not belong to the line, because they were always detached and acted in front of the main body. Grenadiers and light infantry, when from their several corps, cannot be called the line, but the instant they are incorporated they become so. According to this explanation, and we think it a correct one, the word is very generally misapplied, as it cannot strictly be used to distinguish any particular establishment from another.
Line, or line of battle, is the arrangement or disposition of an army for battle: its front being extended along a straight line as far as the ground will permit, in order that the several corps of cavalry and infantry which compose it, may not be cut off or flanked by the enemy.
The Ottoman troops are generally drawn up on a curve line, or half-moon, for the purpose of surrounding their enemies by superior numbers. European armies are usually drawn up in three lines; the first being named the van, (avant-garde, Fr.) the second, main body, (corps de bataille, Fr.) and the third, which was formerly the weakest, is called the reserve, or rear-guard. (Corps de réserve, ou arrière-garde, Fr.) Each of these lines is so drawn up, that the wings or extremities are always composed of some squadrons of horse, whose intervals are likewise supported by infantry platoons. The battalions are posted in the centre of each line; sometimes they are intermixed with squadrons of horse, when there is a considerable body of cavalry attached to the army. The space of ground, which in each line separates the different corps from one another, is always equal in extent to the front that is occupied by them. These intervals are left in order to facilitate their several movements, and to enable them to charge the enemy without being exposed to confusion and disorder. It must be observed, as a general rule, that the intervals or spaces which are between each battalion and squadron belonging to the second line should invariably correspond with the ground that is occupied by the battalions and squadrons, which constitute the first line; in order that the first line, on being forced to fall back, may find sufficient ground to rally upon, and not endanger the disposition of the second line, by precipitately crowding on it.
Each line is divided into right and left wings. Each wing is composed of one or more divisions. Each division is composed of one or more brigades. Each brigade is formed of two, three, or four, or more battalions.
Battalions are formed in line at a distance of twelve paces from each other, and this interval is occupied by two or more cannon, which are attached to each battalion. There is no increased distance betwixt brigades, unless particular circumstances attend it. In exercise, should there be no cannon betwixt the battalions, the interval may be reduced to six paces.
Line, how regulated. Its regulating body in movement is, in general, the battalion of that flank which is nearest to, and is to preserve the appui, or which is to make the attack. There are very few cases in which the centre ought to regulate, although the direct march of the line in front appears to be the easiest conducted by a battalion of the centre. It is the flank, however, that must preserve the line of appui in all movements in front, if the line is thrown backward or forward, it is generally on a flank point.
It may not be superfluous to remark, that the term line, as expressing a military disposition for battle, was not known until the sixteenth century.—Before that period when armies were ranged in order of battle upon three lines; the first line was called advanced guard, (avant garde,) the second, main body only, (corps de bataille,) and the third, rear guard, (arriére garde.)—These terms are never used in modern times, except when any army is on its march; when drawn up for action, or in the field for review, columns, or lines are substituted.
Lines of support, are lines of attack, which are formed to support one another. Where there are several, the second should outflank the first, the third the second; the advanced one being thereby strengthened and supported on its outward wing.
Line of march. The regular and tactical succession of the component parts of an army that is put in motion.