Part 159

In the examination which was made of the relief proposed by me; some persons well acquainted with the particular subject, objected to its adoption on account of the expence. I made an accurate calculation of the amount, and I found that it cost a sixth more than the usual fortification. This does not assuredly form sufficient ground to outbalance the many advantages which can be derived from the construction. Besides, there is no occasion of fortifying all the parts of a town in this manner, since it would be advisable to strengthen the weak points only.”

The construction which is proposed in this new method, is simple, and easily understood. The principal objects to be attended to are these; that there be mines under all the works, and that a regular communication be kept up with the chambers by means of subterraneous galleries, which must be resorted to in proportion as the enemy approaches.

The Piedmontese engineer, from whom we have made these extracts, has added to Vauban’s and Coehorn’s systems. We leave the subject to the consideration of those professional men who have made the art of fortification their peculiar study; they must determine whether the theory of the proposed method be susceptible of practice, and if so, whether it can be rendered so generally useful, as the author seems to promise it would.

On a general view of the subject it must, however, be acknowleged, that a situation is not always found which will admit of the improvements and additions that might otherwise be made. There are some old places in which the figure of the fortifications erected for their defence, is so strange and whimsical, that the least correction of its errors, must be attended with an enormous expence.

A town may be irregularly fortified, and owe that irregularity either to the figure of the works only, by the angles not being equally distant from the centre, although every one may admit of a good bastion, and the lines be tolerably extensive; or by the figure and the angles differing, from some being too acute, and others being rentrant; or by the inequality of the figure and its sides; some being too long and others too short; or finally by a disparity all together in the figure, in its sides and angles.

If the three first kinds of irregularity are judiciously corrected, the correction of the fourth follows of course, as it is only the natural consequence of the others. Those irregularities may be occasioned by a neighboring river, by the entrance into a creek or harbor, or by steep rocks beyond which it is impossible to carry the works.

It is a sound and general maxim in the art of fortifying, to reduce the irregular proportions of its lines, &c. of defence to as much regularity as the ground and situation will permit. For by so doing, their strength becomes equally great throughout. If you should not be able to surmount the natural obstacle which may be thrown in your way, you must never deviate from the general rules that are laid down in regular fortification. These are, that all the parts be well flanked, that the angles of the bastions do not fall under sixty degrees, that the line of defence be within musquet shot, or that outworks be established to bring it within that range; and finally, that the means of resistance be distributed in as many equal proportions as the irregularity of the works will suffer.

You must, however, be careful to avoid an error into which many have fallen. You must not weaken the collective means of defence, in order to strengthen any particular vulnerable quarter; for by so doing you are sacrificing a great line of defence, to the security of a small part which might be strengthened by outworks.

The author of Oeuvres Militaires, in his 3d volume, page 45, has given observations and maxims relative to irregular fortification.

Baron d’Espagnac, in consequence of the remarks which are made by Marshal Saxe, in his Reveries, has in his supplement to that work amply discussed the subject of fortification, and described the different means of attack and defence. We refer the inquisitive officer to those works. Before we conclude these interesting remarks upon an art, which is certainly equal to any invention that has employed the skill and ingenuity of man, we must observe that in all periods, productions on that head have been as numerous as the subject has hitherto proved inexhaustible. It must, however, be acknowleged with some regret, that the tendency of the greater part, if not of all, seems to be an indiscriminate and bold attack upon the works of the immortal Vauban. These writers censure the methods of that great engineer by proposing something of their own, which only differs in appearance, and which they think proper to call a superior system. Assertions, and promises to afford new lights upon the science of fortification, have always, in fact, been profusely given by authors of this description. Their labors, however, are only so far to be regarded and esteemed, in as much as their different systems tend to point out the necessary calculations which are required to shew the expence attending their construction, and to prove the effects they might produce. The memoirs upon perpendicular fortification, written by M. Montalembert engineer, will throw considerable light upon these observations.

With respect to the knowlege of fortification, it must be manifest to every thinking man, that from a chief magistrate, or head of a country, down to the lowest infantry officer, the acquirement of it is more or less indispensibly necessary.

A chief magistrate of a country, should be well versed in the science of fortification, in order to examine the plans that are laid before him, and to determine upon the execution of proposed projects.

A secretary of war should know it, in order to explain the nature of the plans when questioned by a superior power, to calculate the expences which will attend the construction of works, and to distinguish good ones from those which might be useless and expensive.

Every commandant of a town or fortified place, should be well acquainted with the subject, because it may fall to his peculiar share to construct works in cases of emergency, or to add to those already erected for the defence of the place entrusted to his care. He likewise ought, at all times, to be able to ascertain how far such a place is capable of holding out.

Every director of fortification should be master of it, in order to discriminate between what is proper, or what is defective, and make his report accordingly.

Every infantry officer, in a word, should be conversant in field fortification at least, if not acquainted with the general system. For without some knowlege of its branches, how will he, in cases of emergency, be capable of throwing up a temporary redoubt, of fortifying a spot of ground which he is ordered to maintain, or of securing a common outpost?

Field FORTIFICATIONS, fortifications de campagne, Fr. consist in the art of fortifying, constructing, attacking, and defending all sorts of temporary field works during a campaign.

Although an engineer may be perfectly master of the different methods by which a town can be strengthened and secured by permanent works, he should not remain satisfied with that acquisition, but carefully direct his attention to the distribution of ground, for field fortification. He should be able to ascertain, with geometrical precision, all the relative divisions and corresponding points of any situation in which it might be judged expedient to construct that species of fortification which consists in intrenched lines, fortins, or small forts, and in redoubts of various denominations. The shape or figure of these works is exactly similar to those of the permanent kind. Ditches, ramparts, and parapets must be dug and thrown up, to secure the former, in the same manner as they are practised for the protection of the latter. They only differ in their measurement and proportions. Intrenched lines are made for the purpose of covering a camp from any sudden insult of the enemy, which should always, on this account, be pitched in the most advantageous manner; contiguous to and facing that quarter where it is probable the attack will be made, a ditch must be dug, having three toises at least in width and two in depth. This must be defended by a parapet en redans, or be occasionally flanked with small bastions, two toises thick, consisting of solid good earth well pressed together, covered and supported with fascines; having likewise banquettes behind them sufficiently high to conceal the soldiers’ tents. If water could be conveyed, or drawn into the ditch from any adjacent rivulet, or river, the security would be greater. When the lines of intrenchment are thrown up with an intention to maintain the ground any length of time, a covert-way must be made, which should be regularly fenced with palisades.

There is another species of field fortifications, which is resorted to in order to keep up a communication between two places; in which case great care must be taken to prevent the lines from being enfiladed in any quarter; and if they should be exposed in that manner, no time ought to be lost in strengthening the weak points by constructing redoubts, or small forts. The defence of these redoubts and forts must be entrusted to small arms and musquetry, but not to cannon, as the range of the latter is always too extensive to prevent an enemy’s close approaches to the lines of communication from their field works, or forts. Necessary drains must be made to let out the water that collects, as it would otherwise destroy the works, drown the sentries, and cut off all communication with the main body.

When a position is taken upon a steep rock, or eminence extremely difficult of access, the lines which surround it do not absolutely require ditches for their safety, as the parapet and banquette may probably be sufficient; but if any vulnerable or weak part be observed, every effort should be used to get at a spring, and to fill up an excavation in front of it, to prevent surprises. An able engineer will be particularly careful in drawing his plan of communication, to ascertain the exact points whereby they may be protected by an enfilade from one fort to another; so that if the enemy should make a lodgment any where, he will not be able to maintain his position on account of his being flanked by other works.

Field works, or small forts are generally constructed in places the preservation of which is judged to be indispensibly necessary. Such, for instance, are necks of land that stretch into a marsh, and are surrounded by it; the passage of a road, têtes de ponts, or heads of bridges, and other objects of similar importance in offensive, or defensive operations. On these occasions the shape and size of the construction must depend upon the nature of the ground, the importance of the undertaking, and on the number of men by which the works are to be garrisoned.

Many forts in field fortification are built in triangular forms; some are square, some starred, or en étoile, some as redoubts, in the shape of demi-lunes, others in crown, or horn-work, and others again in the figures of tenailles or queues d’hirondelle.

When the object of defence is a windmill, a castle, or a small dwelling-house, the first step to be taken, is to select a spot of ground upon which you are to build the field work, so as to check and prevent the enemy’s approaches. In order to do this effectually, the shape and adjacent parts of the building must be closely attended to, and the work be thrown up without exposing it to a rear attack; but if the place to be defended stand alone, and be not supported by any ditch or eminence on its flanks, or in its rear, you must then fortify it all round. The earth which is dug out of the ditch will serve to raise the rampart, or parapet. Saliant angles, distributed at equal distances, in the shape of bastions, must be erected with good flanks to protect and cover the intrenchment. If, on account of the ground, the work should not be much raised, the parapet must be raised, in order to prevent the enemy from attempting an easy assault.

An engineer from Piedmont, who has proposed some new methods in field fortification, is decidedly against stone and masonry, in the construction of parapets and field works. His reason is self-evident; for as he justly observes, the scattered pieces which must naturally be thrown about in all directions by the demolishing of the walls in the discharge of heavy cannon, would do more mischief than the cannon itself.

It is frequently found necessary to fortify a bridge; the means adopted for this purpose must depend entirely upon the size and current of the river. If the stream should be broad and navigable, and so far from the fortress, that it cannot be defended by the ordinance of the town or fortified place, in that case a large retrenchment, resembling a place of arms, must be constructed, with strong bastions to support and cover it, curtains and half-moons, a broad and deep ditch, and covert-way that must be well secured by palisades. This retrenchment, or place of arms, must be made sufficiently capacious to hold a garrison that would be capable of opposing the attack of a large detachment from the main army of an enemy. A half-moon must be constructed within the lines, with a ditch in front, to serve as a work behind which the garrison might retreat with its artillery, disputing every inch of ground, and by that means affording sufficient time to cut down the bridge.

If the river should be narrow, yet wide enough to prevent any sudden irruption into the country beyond it, the bridges that are across must be fortified by works made of earth, which are to be covered by ditches dug in front. Half-moons, tenailles, crown and horn-works, and similar constructions, provided they be well fenced with palisades, will answer all the purposes required in such cases. The engineer, by the first glance of his eye, will be able to ascertain the situation of the country, and to fit his plans accordingly. Small lodgments, or wooden recesses, must be made as guard-houses, in which detached parties of men should be stationed to meet the first attacks of the enemy, and to keep him in check while the whole army passes over the river, or is drawn up in order of battle to dispute the passage. These intrenchments must invariably be well furnished with light artillery, for the purpose of annoying the approaching enemy. But the disposition and arrangement of these pieces must always be such as to admit of their being instantly removed, when the intrenchments are carried, under the cover of heavier ordnance which is kept playing upon the enemy from the opposite side of the river.

Practical Maxims in building Field Works. 1st. The spot on which works are to be constructed should determine their figure; nor should any attention be paid to preserve a regular form which does not occupy the ground to advantage.

2d. Every line must be so disposed, that the slope of hills all around even to the very bottom, be open to the small arms of the garrison; and every part should be discoverable to the distance of at least 500 paces.