Civil War Field Fortification
Dennis Hart Mahan
Attack and Defence of Intrenchments
A Transcription of Chapter XI of
A Complete Treatise on Field Fortification
Third Edition, Revised and Enlarged
Pages 92 - 103
Published at New York by John Wiley, 1862
Note:
The eccentricities of Mahan's spelling and punctuation have been retained from the original.
266. Attack. The subject of the attack admits of two natural divisions; the first of which comprehends all the preliminary steps taken before the troops are brought into action; the second all the subsequent operations of the troops.
267. An attack is made either by surprise, or openly. In both cases exact information should be obtained of the approaches to the works; their strength; the number and character of the garrison, and also the character of the commander. This information may be obtained through spies, deserters, prisoners, and others who have access to the works; but implicit faith ought not to be placed in the relations of such persons, as they may be in the interests of the garrison; and in all cases they should be strictly cross-examined and their different representations be carefully compared with each other.
268. The best source of information is an examination, or reconnaissance, made by one or more intelligent officers. This reconnaissance should, if possible, be made secretly; but as this will not be practicable if the garrison show even ordinary vigilance, it will be necessary to protect the reconnoitring officer by small detachments, who drive in the outposts of the garrison. The object to be attained by the reconnaissance is an accurate knowledge of the natural features of the ground exterior to the works; the obstacles it presents, and the shelters it affords to troops advancing; the obstacles in front of the counterscarp and in the ditches; the weak and strong points of the works, and the interior arrangements for the defence. If the work is an isolated post, information should be obtained as to the probability of its being succored in case of attack; the length of time it must hold out to receive succor; and the means it possesses of holding out.
269. Attack by surprise. A surprise is an unexpected attack, for which the assailed are not prepared. It is, perhaps, the best method of assailing an undisciplined and careless garrison, for its suddenness will disconcert and cause immediate confusion.
270. Secresy is the soul of an enterprise of this nature. To ensure it, the garrison, if aware of the presence of the troops, should be deceived and lulled into security by false manoeuvres. The troops that form the expedition should be kept in profound ignorance of its object until they are all assembled at the point from which they are to proceed to the attack.
271. The winter season is the most favorable for a surprise, which should be made about two hours before day, as this is the moment when the sentries are generally least vigilant, and the garrison is in profound sleep; and the attempt, if at first successful, will be facilitated by the approach of day, and if unsuccessful, the troops can withdraw with safety under obscurity of night. Should there be danger, from succors arriving in a short time, the attack should be made soon after midnight, when the garrison is asleep, so that the troops may retire before daylight, after having attained their object.
272. As a general rule, the troops for the attack should consist of a storming party, divided into an advanced party and its support, and be followed by a reserve of picked men. The advance of the storming party will open the way, and be closely followed by the support in the assault of the parapet and a reserve of picked men. There should be two guides, one in front of the storming party, with the detachment of workmen under the command of an engineer officer; the other in the rear, under charge of a guard, to supply the place of the first, if killed. The workmen should be furnished with axes, crowbars, pick-axes, &c., and several bags of powder, of about thirty pounds each, to be attached to palisadings, fraises and barriers, to blow them down, if the alarm should be given whilst they are opening a way through them by other means. All operations should be carried on with despatch and in silence. Should the sentries challenge, they must be secured or bayoneted.
273. Circumstances alone can determine whether it will be advisable to make false attacks with the true one. They will distract the attention of the garrison, if the alarm is given, from the true attack; and a false attack has sometimes succeeded when the true one has failed. When made, one should be directed against the strongest point of the work: as the strong points are usually guarded with less vigilance than the others; and they should all be made at some distance from the true attack; and orders be given to the detachments making them proceed to the point of the true attack, should they succeed in making their way into the work.
If the attack succeeds, immediate measures should be taken to place the works in a state of defence, if the position is to be maintained; or else, they should be destroyed, as far as practicable, before retreating from them.
274. Attack by Open Force. The general arrangements for an open assault, comprehend the operations to gain possession of the works; the measures for maintaining possession of them, and following up the first advantage; and, finally, the precautions to be observed in the event of a repulse.
275. An open assault may be made either with the bayonet alone, or with the combined action of artillery and the bayonet. The first is the most expeditious method, but it is attended with great destruction of life; it should therefore only be resorted to against works of a weak character, which are feebly guarded; or against isolated posts within reach of speedy succor. When tried it will usually be best to make the attack before day. If it is made by daylight it will, in most cases, be well to pick up patroles and stragglers who might give the alarm, and then push forward rapidly the assaulting columns. If the assailed seem prepared, light troops should precede the columns of attack, with orders to display in front of the counterscarp, and open a brisk fire on the assailed, for the purpose of diverting their attention from the columns of attack.
276. In an attack with artillery, the troops are drawn up in a sheltered position, or beyond the range of the guns of the assailed; batteries are then established within about six hundred yards of the works, in the most favorable positions to enfilade the faces, and destroy all visible obstacles. The batteries keep up an incessant fire of ball and hollow projectiles, in order to dismount the cannon, and create confusion among the assailed. When the fire of the works is silenced, the troops are brought forward, and demonstrations are made on several points, to divert the attention of the assailed from the true point of attack, and prevent him from concentrating his strength on that point. Several false attacks should be made at the same moment with the real one, and each of them should be sufficiently formidable, in point of numbers, to enable the troops to profit by any success they may obtain.
277. The number and disposition of the troops making the assault will depend, in so great a degree, on local circumstances, and the arrangements of the assailed, that nothing more can be laid down under this head than some general rules.
278. The attack should be led by a storming party, composed of picked troops, or of volunteers for the occasion; this party is preceded by a detachment of engineer troops, provided with the necessary means to make their way through all obstacles, to enable the storming party to assault with the bayonet. If the detachment is arrested at the crest of the counterscarp, by obstacles which must be destroyed before farther progress can be made, the leading files of the storming party may open a fire on the assailed to divert their fire from the workmen; but this operation should only be resorted to from necessity, as it breaks in on that unity so essential in an operation of this character, and impairs the confidence of the soldier in the bayonet, on which his sole reliance, in such cases, should be placed.
279. The storming party should be provided with light scaling ladders, planks, fascines, strong hurdles, &c., for the purpose of descending into the ditch; to mount the scarp; to cover trous-de-loup, small pickets, &c., &c.
280. Another detachment of engineer troops follows in rear of the storming party; its duties consist in rendering the passages, opened by the first detachment, more accessible to the troops, who immediately follow it to sustain the storming party. The second detachment is also charged with the care of placing the work from which the assailed has been driven in a defensive attitude, in order to frustrate his attempt to repossess himself of it. The first detachment should be charged with this duties: for, independently of having handsomely acquitted itself in bearing the brunt of the action, it may be required to precede the storming party in the pursuit of the assailed to his interior works.
281. The troops destined to support and, if necessary, reinforce the storming party, advance in one or two lines, with cavalry, and some pieces of artillery on the wings, to repel sorties. The remainder of the troops follow in order of battle, to improve the first successes, or to cover the retreat of the assaulting columns, if repulsed.
282. The salients are generally the points on which the storming party advances, unless some natural feature of the ground should present greater facilities for advancing on a re-entering, or in front of a face. When the ditch is gained, shelter is sought in a dead angle; and if the work is fraised, or resolutely defended with the bayonet, a breach must be made, either into the parapet, or by undermining the scarp with the pick. If the intrenchments consist of detached lunettes, an attack should be made on their gorge at the same moment with the one in front.
283. When the assailed are driven from their main works, the storming party should press hotly on their rear, and endeavor to enter pell-mell with them into their interior works, leaving to the troops which follow them the care of retaining possession of the works gained; but if the intrenchments are supported by other troops drawn up in order of battle, the storming party should halt in the works until it is reinforced by the troops in its rear.
284. There is no danger to be apprehended, in case of a retreat, after an unsuccessful attack on an isolated work. But in an attack on intrenchments, supported by an army, the retreat of the storming party should be covered by cavalry and artillery, until it can find safety behind the main body of troops, drawn up in order of battle to protect it, and to receive the assault of the assailed, should he attempt offensive operations.
285. In conducting the attack, preparations should be made beforehand for removing all the artificial obstacles that the assailed may have placed before their works, to impede the progress of the storming party. This duty is usually intrusted to the detachment of engineer troops, who are provided with axes, picks, and other suitable tools for this purpose. When the obstacles are of a nature to be easily destroyed by artillery, it should always be resorted to. Abattis, palisades, fraises, and entanglements, when exposed, may be readily torn to pieces by opening an enfilading ricochet fire on them. When cannon cannot be brought to bear on these obstacles, an abattis may sometimes be set fire to, and palisades, &c., be blown in by attaching bags of powder to them. Trous-de-loup may be passed, either by covering them with plank or strong hurdles, or else by directing the men to pass cautiously between them in extended order; small pickets may be broken down, or else fascines may be spread over them so as to form a tolerable stable road-way. fascines may also be used to cover the points of spikes.
286. The passage of the ditch, and the assault of the parapet, are the most difficult operations. If the ditch is not more than six feet deep, it can be leapt into without danger, and the men can mount the scarp readily with very little assistance from each other. When the width is not greater than twelve feet, the ditch may be crossed by laying thick plank, or small scantling over it. When the depth is over six feet, the storming party is usually provided, either with small scaling ladders, or with fascines, sand-bags, or other means, to fill the ditch partly up; or if these means cannot be procured, the detachment dig away the counterscarp into steps, throwing the earth into the ditch, and thus, in a short time, form an easy entrance to it. Wet ditches may be filled up either will sand-bags alone, or more expeditiously by attaching sand-bags to large fascines, or to trusses of hay or straw.
287. The assault of the parapet is made by the aid of scaling ladders, or by effecting a breach, by firing loaded hollow projectiles into the scarp and parapet, which, by their explosion, crumble the earth down, so as to form an accessible ramp; or else the foot of the scarp is undermined with the pick, and the mass of the parapet tumbled into the ditch.
288. Defence. The essential point in the defence is to have every part of the works guarded by a sufficient number of troops to resist an attack on all sides. This is of importance not only in isolated works, which can be surrounded, but also in continued lines; for although the enemy will usually make an attempt to enter only at a few points, still the confusion and delay which might arise from changing the position of the troops, to meet the movements of the enemy, particularly in a night attack, would be extremely hazardous.
289. A vigorous defence will require, at least, two ranks to be drawn up on the banquette throughout the entire extent of the line, with supports, and a reserve proportioned to the importance of the work.
290. The strictest vigilance should be exerted to guard against a surprise; for this purpose sentries should be posted on all of the most commanding points of the works; and on the exterior, at such points as the enemy might approach unseen, as roads, fords, defiles, bridges, &c.; besides these, small detachments of picked men should be stationed to watch these accessible points, and all other places where the enemy might secrete himself, or approach unexposed to the fire of the works. Patroles should be sent out to watch the enemy's movements, and to have an eye on the manner in which the sentries perform their duties. The patroles are particularly charged with the duty of preventing the enemy from reconnoitring the approaches to the works; to do which effectually, without giving unnecessary alarms, they should be ordered to attack with the bayonet alone, unless surprised by an ambuscade.
291. At night the number of sentries should be increased; and redoubled vigilance be used, particularly after midnight. If there are well grounded apprehensions of an attack, fire-balls may be thrown out, or fires be lighted in front of the works, to discover the approach of the enemy. Occasional false alarms should be made to keep the garrison on the alert; but this artifice should not be too often practised, otherwise it might produce a contrary effect besides[;] all useless fatigue should be spared men who are sufficiently harassed by the ordinary duties of their situation.
292. In conducting the defence, each corps should have its particular post assigned to it; and receive special instructions relative to the part it will have to play. Too much attention cannot be bestowed on the part of the commanding officer in seeing that his subordinates are thoroughly conversant with the character of the defence, and all of the resources that can be drawn from their position; and that this knowledge be imparted by them to the non-commissioned officers, and even to the most intelligent among the privates. The fate of a work may depend upon the good or bad conduct of one individual. The reserve is posted in the most convenient position to afford prompt assistance to any point in danger of being forced. The troops drawn up on the banquette should be carefully instructed in their duties; and they should be taught not to look for aid, or relief, from the reserve, until they have repulsed the enemy.
293. If the enemy opens his attack by a warm cannonade, the troops should not be exposed to it, if they can be sheltered near the posts they are to occupy when his columns of attack approach, at which time his cannonade must cease, in order not to injure his own troops. The men should be instructed to reserve their fire until the enemy has arrived at certain points out in front of the works, which should not be farther than two hundred yards from the parapet.
294. Sorties, if well timed, will generally decide the fate of the affair. They should be made when the column is thrown into confusion, or shows any signs of irresolution in its movements; or when its flank, or rear, is carelessly exposed. They are sometimes made to alarm the enemy for his own safety; or to make a diversion in favor of expected succors in blockaded posts.
295. Cavalry is the best arm for a sortie, on account of the rapidity of its movements, and the violence of its shock. When infantry is employed for this purpose, it should use the bayonet alone.
296. Should the enemy succeed in forcing his way into the work, the reserve should attack with the bayonet, before he has time to form; but it must be confessed that success oftener crowns an offensive movement, on the part of the assailed, in endeavoring to regain possession of their works, than any effort to drive back the enemy at the moment, when flushed with success, he has the hope of a certain victory. The only well-grounded prospect that the assailed have of repelling the assault, when the enemy has gained the top of the scarp, is to meet him in an offensive attitude at the point of the bayonet on top of the parapet.
297. The particular arrangements of the defence consist in defending all obstacles, such as abattis, palisadings, &c., by a warm well-aimed fire; as the particular object of these obstacles is to keep the enemy exposed for a longer time to the fire.
298. Large stones, heavy round logs, and loaded hollow projectiles, should be in readiness to be rolled over on the enemy whilst he is in the ditch endeavoring to mount the scarp. Large branches of trees prepared as for an abattis, with chevaux-de-frise, the other obstacles, should be at hand to obstruct the breach.
299. Finally, in an isolated post, if the enemy after having been repulsed, makes a show of blockading it, or of renewing his attack, and there is no prospect of succor arriving, the garrison should attempt to escape by night.
Mahan's Principles Dufour Duparcq Regulations Jebb Barnard
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