When a town is set on fire, the inhabitants usually in treat or compel the commandant to surrender.
Should the enemy undertake a sortie, or if a gate can by any means be penetrated, it will hasten the surrender of the town. In all cases, however, the retreat of the enemy is if possible to be cut off.
A most advantageous attack of such a town is made by tirailleurs, in the same manner as has been explain ed in the Section on the Attack of Permanent Fortifications.
Sketch of CAnNoT's Method of Defending Fortified Places.
From the account which we have now given of the at tack and defence of fortified places, the reader must have observed, that when a fortress is regularly invested, how ever strong it may be, its fall after a certain period is con sidered as a matter of course. The maximum of that pe riod we formerly stated at 90 days. In the actual state of things, however, it seldom exceeds the half of that, and even this is considered a good defence. In proof of these remarks, we subjoin the calculation which Vauban gives of the duration of the siege, supposing the place to be strongly fortified and well garlisoned.
We have already observed, that the application of such calculations to the operations of moral causes, may per haps at first sight appear absurd. It is to be remember ed, however, that from the superior force which the be siegers can always command, it is impossible that any place can hold out for an indefinite period. It seems reasonable, therefore, that certain laws should be established among nations with regard to the surrender of fortified places, in order to prevent the obstinacy of an individual being the cause of an unnecessary effusion of human blood. Such laws have accordingly been generally recognised, and those who persevere in their defence of a place, after it ought by these laws to surrender, arc considered as having de prived themselves of the privileges usually granted to pri soners of war. A modern writer on fortification, M. now Count Cannot, has, however, advanced a very different doc trine. Reasoning on that fundamental principle of milita ry discipline, that every soldier ought to die rather than give up his post, he maintains, that such calculations as we have detailed above, are generally false, and that, when they are true, they tend only to crush the spirits and para lyze the efforts of the defenders. He considers the cou rage and determined perseverance of the garrison as the strongest bulwark, and therefore condemns every thing that tends in the slightest degree to depress or extinguish these. Such reasoning, however, would scarcely be end tled to notice, and certainly would never contribute, in any essential degree, to prolong the defence of a place, unless it were accompanied with something more substantial than mere declamation. To support his arguments, therefore,
Cannot has proposed a new system of defence, against which he considers the present method of attack altogeth er inefficient. Admitting what, indeed, cannot be denied, that if the besiegers are permitted to proceed step by step with their approaches and parallels, as in the ordinary way, the guns of the fortress will soon be silenced, and the fall of the place must follow ; he sets out with slicwing how the progress of the enemy is to be retarded. This is prin cipally to be done by irregular sorties, so contrived, that the sallying force may always be greater than the force to be attacked. The sallies commonly made in the present system of defence are too regular to be effectual. They are always made at the same points, where, of course, the enemy is always prepared to receive them ; so that, be fore they can succeed in destroying any of the works, they must combat a superior force. But by contriving to have a great number of points from which sorties can be made, the garrison may have frequent opportunities of attacking an inferior force, so as to insure success in destroying the works intended, without sustaining any considerable loss. By these, frequently repeated, the enemy's progress is re tarded, his troops are harassed, and he is obliged to em ploy a much greater number in defending his workmen, as it is only by a very strong guard at every possible point of attack, that he can protect his intrenchments from the dis astrous effects of these sorties. But even should he have men enough to form sufficient guards on every part of his works, by crowding great numbers into one place, lie only exposes them to a more certain destruction, from the im mense number of vertical fires (feux verticaux), which form the second, and indeed the principal part, of Carnot's method of defence. These consist of mortars of different calibres, elevated at an angle of about 45 degrees behind the parapet, and covered by blindages. In this way, the guns themselves, as well as the men who work them, are completely protected, both from the direct and ricochett fire of the enemy. When used, they are loaded with a charge sufficient to carry the shot to such a height, as that, by its descent, it shall acquire velocity enough to prove fatal to the person whom it may strike. Of the effect produced by these vertical fires, when substituted for the greater part of horizontal guns, in a garrison of an ordi nary size and strength, Carnot gives the following calcula tion.