DEFINITIONS.

The "Theatre of War" is the whole area of country in any part of which the hostile armies can come into collision with one another.

The "Base of Operations" of an army is the point, line, or district from which it starts, and from which all its reinforcements and supplies proceed when it is committed in a campaign. It may be a single town; it may be a frontier line of any length; or a line of sea-coast, if the army possess the command of the sea; or it may be a district of country having breadth as well as length. Whatever be its nature, it must be such that the army retreating upon it in case of disaster shall, on reaching it, find succour and safety.

The tactical and strategical base of an army is the same. Defeated in a battle, it must retire in some direction; and it is plain that the only safe retreat is that which leads direct to its base. For if the victorious army should interpose between the defeated army and its base, the reinforcements and supplies of the latter would be cut off, and the probability would be the entire disorganisation and

dispersion of the defeated army, a probabiltiy to be guarded against with the most anxious care.

It is certainly quite possible that an army which has been cut off from its base may fight a victorious battle, its face towards its natural point of retreat, with an enemy who, although he has interposed between the army and its base, may still have his own line of retreat secured. But in such a case the army fights a battle for existence whose loss would be total ruin, while the enemy fights in comparative safety.

The "Line of Operation" of an army is the line by which it advances from its base into the theatre of war. It must not be supposed to signify one road only; it embraces every road by which the fractions of the army march. A large force may thus include a considerable breadth of country in the march of its columns. When all the marching fractions are in communication with each other, the army's line of march is called a "single line of operation." But if the fractions of an army marching towards the same point are unable to communicate with each other, either by reason of distance or of any natural obstacle, the army then has as many lines of operation as there are separated fractions.

The "Communications" of an army, as the name implies, are the lines by which it communicates with its base from any point to which it has advanced

in the theatre of war,- along which its reinforcements and supplies must pass to reach the army, and by which it must retreat in case of disaster; and the definition applies equally, whether the army occupies an extended strategical front, or is united on a field of battle.

In general the communications are along the line by which it has advanced, or along its line of operations, but not always. This will be made clear

hereafter.

"Interior Lines of Operation" are the lines by which a force, of whatever size, marches to unite at any given point, provided those lines are shorter than any by which an enemy can unite an equal force at the same point.

From this it follows that lines are exterior or interior solely with reference to those of an enemy. Without the presence of an enemy on the theatre of war, no lines however circuitous would be exterior; none however direct interior.

The terms of the definition are subject to modification from the relative circumstances of the armies. For instance, if a General in command of an inferior force to that of an enemy has been able to unite his whole force at a given point, while his enemy has there been able to unite only a fraction of his force, that General has moved on interior lines, notwithstanding that his united force may be numerically weaker than the fraction of the enemy.

The accompanying diagram illustrating the simplest case that can arise, may serve to fix the meaning.

12

88

A is an army occupying the position a, in the centre of a circle, of which b1, b2, b3, is part of the circumference. B is an army whose fractions are at

b1, b2, b3. Suppose the radius of the circle, and the distances b1 b2, b2 b3, to be all equal. Now, if A marches against B's centre fraction b2, no advantage is gained, as the two extreme fractions of B can arrive at b2 as soon as A; and both armies are united at b2 at the same time. But if a marches from a on either b1 or b3, A will arrive at either of these points united in a time in which в is able to unite only two of its fractions at the same point. A has then moved on "interior lines."

It is not the mere distance in miles which an army must march which decides the question of exterior or interior lines; it is the number of days' marches represented by that distance, which must be calculated on the data explained in the introductory chapter.

This definition applies equally to the movements

of armies on a field of battle. The first are called "interior strategical lines," the last "interior tactical lines."

An army is said "to cover a certain line or district," when it is able to reach every point in either in a shorter time than an enemy requires to reach the same point. In this case the army covers or protects the line or district directly. Two armies, A and B, are at a and b respectively; e, the middle point between them. A evidently covers directly every point in the line c d, and in rear of it, from the attacks of B; A likewise protects directly every point in rear of the line ef, because the distance of

such point from a will be less than from b. For distance substitute the number of marches represented by that distance, calculated on proper data, and the illustration applies to any configuration of country. But A will also protect indirectly any points, x, x', whose distance from b is greater than that of a from b, provided в's line of retreat necessarily passes through b,— because in this case if B