Echellon movements of an army are almost always those which are made when hi presence of the enemy, the inequalities of ground generally preventing large bodies of troops, if it were otherwise advisable to do so, from acting against one another in continuous lines. Like the echellon movements of battalions, those of an army may be either direct or oblique : the former are executed by advancing brigades, battalions, or companies parallel to and at unequal distances from their front ; and this advance may be made from tho centre of the line when it is Intended to refuse both wings to an enemy, or from one flank when it is Intended to turn that of the enemy. The direct echellon may also be produced by posting columns In proper situations, ready for deployment, parallel to the euelnys position : the distances between the battalions in echellon should be sufficient to allow them to form squares ellecqiienvise, so as to flank one another.
Oblique echellons of an army are formed by wheeling, and then marching in the new directions so as to gain ground obliquely towards a flank ; each of the several bodies performing the manoeuvre should not exceed a company, as it might be It:manhole, to present one flank of a large body towards an enemy in position, and thus expose the line to be enfiladed. And, as the enemy would endeavour to counteract the intended project of outflanking him, should he observe it, advantage ought to be taken of the localities to conceal some of the divisions, and to gain points of support for the bodies placed in advance of the rest of the army. When it is intended to refuse one wing, the battalions of that wing may retreat en echelon as far as necessary, and the artillery of that part of the line which is stationary should be rea'ly to enfilade the enemy on his advance towards the retiring divisions. Movements of attack may he made in columns, which should deploy in line at from 1200 to 1400 paces from the enemy ; the destructive effects of an enfilading fire preventing a nearer approach in column.
Generally speaking, the most convenient order for an army, whether on the offensive or defensive, is in column, provided the columns can be covered by the ground from the enemy's artillery ; since it may be readily moved up to any given point of attack, while the enemy has few means of judging where that point of attack will be. • Changes in the front of a position, when under fire, are best effected by an echellon march of companies; but when the line is extensive, the battalions which are moat remote from the new alignement and which may be attacked by cavalry during the movement, should be marched up in columns of battalions, the divisions being at quarter distances from one another.
The retreat of a line is accomplished by causing each alternate battalion to retire, perpendicularly to the front, to a certain distance towards the rear, not exceeding 200 yards. that the divisions may be able to support each other by their fires ; the remaining battalions pro tecting the retreat of the others, and then retiring as far as the intervals between the former battalions, who then retreat still further, and so on. The intervals in the lines should be occupied by light infantry ; and if the enemy should press closely, the second line of the army, after the first battalions have passed through it, must contribute by its fire to the defence of the intervals in the first line.
This retreat by alternate battalions, or by half-battalions, is indis pensable when it is made over a plain ; and if the retreat is to be continued, defiles and commanding spots of ground must be occupied and defended as long as possible ; by degrees the bodies may diminish their fronts and form themselves into columns of march.
If a gradual retreat of the whole line is not intended, on a flank of the army being attacked, that flank only may be retired in direct echellon by alternate battalions or half-battalions, beginning with that which is at the extremity of the flank attacked; the remaining battalions then retire, still en &teflon, thus keeping the menaced flank refused to the enemy, taking care that the distances between the corps are not so great as to render it impossible for them to defend each other by their tire. Each body must repel an attack, if made upon it by infantry, by a counter-attack ; if by cavalry, it may dispose itself in a square ; or a new line may be formed in the oblique position, if it-be thought best thus to resist a general attack of the enemy.
The movements of the second line of an army should correspond exactly to those of the first, the two lines always preserving their parallelism and distance. The second is however frequently kept in a line of columns of battalions, and is made to move in that order even when the first line is deployed.
The most proper stations for cavalry are on the wings of an army, because troops of this class are unfit for resisting an attack ; and should they be compelled to retire when placed in the centre, there would be left au interval which the enemy might immediately occupy, and from thence enfilade the wings. This false disposition was made by the French at the battles of Hochstet and Minden, and was the cause of their defeat in those actions. Cavalry are generally employed in the operation of turtling a line ; and it is evideut that this manoeuvre must be more readily made from the nearest wing than from the centre.