The fallowing general rules are to be observed, with respect to the position of the main army and its de tached corps. 1. The main army must never weaken itself so much by detachments, as to be under any ap prehensions for its own safety. 2. No corps must be detached in such a way as to he exposed to danger. 3. In sending out detachments, we must always pro vide for the junction of the whole army on the neces sary point, to secure its safety, or to execute the pro posed enterprise, or any other that may offer. Be sides, the position of every detached corps must be chosen, so as to enable it to execute an enterprise dan gerous to the enemy, and at the same time, if opposed, to have the means of executing some other.
In a defensive war, the art of positions is of the greatest consequence. 1. A position may be chosen which covers the whole parallel. Such a position must be strong in itself; the enemy must not be able to get round it at all, or only with his whole army, and that not without exposing his own parallel or communica tions. 2. The position may cover the greater part of the parallel. Such a position, besides being strong, must have obstacles on both sides, which, although they do not reach to the end of the parallel, force the enemy to make a large circuit to get round, while he can be opposed by a much shorter movement. 3. The position may be such that the parallel can be covered only by manoeuvres. This may be done in three ways. In the first place, a central position is chosen fur the whole army, from which the object of every movement made by the enemy may be frustrated by a shorter movement. In the second place, we may follow the enemy in all his movements, always choosing positions of proper strength, and so near to him, that, from fear of being himself attacked, he can undertake nothing, unless with his combined force. In these circumstances, we must endeavour to beat, or at least annoy, all his convoys, foraging parties, and detachments. Thirdly, we may extend our line in proportion as he extends his. When he makes a movement in his parallel, we make a corresponding one in ours; when he detaches a corps, we do the same, always calculating the time it will require to join the main body, in order that we may always be in a situation to unite more rapidly than the enemy. Should he expose a detachment, a com munication, or magazine, we must endeavour to take advantage of the opportunity, and to change the rela tive situation of the war. We must beware, however, of committing any such fault ourselves, and that is a matter of great difficulty ; for as the enemy begins all movements, and we must regulate all ours by his, it is scarcely possible to avoid some dangerous exposure. Hence, this method is the most hazardous of all.
An army with both flanks secure against the possi bility of being turned, is in a most advantageous post ; but where defensive measures are to be literally fol lowed, such positions will seldom occur. It is more easy to gain a flank in an open country, it is more de cisive where there are mountains; because, in moun tainous ground, the enemy may be hemmed in, and cut off from its magazines. These are, indeed, ma noeuvres of a delicate nature, which require to be con ducted by a general possessed of more than ordinary abilities, and commanding an excellent army. \Vith these advantages, the assailant certainly has the best chances of suct.css, provided he is sufficiently cautious in chusing positions which do not expose his own com munications to a counter operation on his flank or rear, by which the enemy might force him to fight on disad vantageous terms. No corps whatever must be posted in a valley, unless we are masters of the mountains which form it ; and if we cannot occupy both sides, we must at least occupy one ; for though, at first sight, mountains, rocks, and woods, may appear impassable, yet, upon a diligent inquiry, the contrary will be al ways found ; for in every country that is well peopled, there are, and must be, communications between the villages, at least for infantry. We ought, therefore, to occupy the mountains and woods with our infantry, and the valley beneath with our cavalry, which will hinder any enemy from passing through it.
The conduct of a defensive war is always a matter of great difficulty. In defending a province, it is ne cessary that our movements in every direction along its frontiers may be made with facility ; or, that a po sition be selected, which the enemy cannot attack with the prospect of success, nor turn without being exposed to be cut off from his own magazines and line of ope rations; in short, a position from which he cannot force is to retreat. Posts of this description, however, are rarely to be found; for if the enemy be active, reso lute, fertile in resources, and possessed of an army well versed in manoeuvres, he will constantly find means to penetrate, at least with infantry, and turn our flanks. The attempt to cover every town and vil lage will always be found impracticable. The perfec tion of defensive war consists in preventing an enemy from obtaining any advantages, which may enable him to accomplish his main object. When, therefore, the precautions are so carefully taken, that at the end of the campaign he finds himself no nearer the attain ment of this object than he was at the beginning, then a defensive war has been properly conducted, notwith standing any other advantages or acquisitions of tory he may have obtained.