Elements of Military Art and Science - Henry Wager Halleck (best free ebook reader .TXT) 📗

A floating body, propelled from one bank to the other by the current of the stream, is termed a flying-bridge. The usual mode of establishing a ferry of this kind, is to attach the head of the boat by means of a cable and anchor to some point near the middle of the stream. By steering obliquely to the current, the boat may be made to cross and recross at the same point. A single passage may be made in the same way, by the action of the current without the cable and anchor, but the boat in this case will be carried some distance down the stream. Rowboats are employed for crossing over infantry by successive debarkations; but this process is too slow for the passage of a large force; it may very well be resorted to as auxiliary to other means.

Steam craft are so common at the present day on all navigable streams, that an army in the field will frequently be able to avail itself of this means of passing the larger rivers. But, in a hostile country, or in one already passed over by the enemy, it will not be safe to rely with confidence upon obtaining craft of this character. A well-organized army will always carry in its train the means of effecting a certain and speedy passage of all water-courses that may intercept its line of march.

Flying-bridges or rowboats were employed in the passage of the Dwina, in 1701, by the Swedes; the passage of the Po, in 1701, by Prince Eugene; the passage of the Rhine, at Huninguen, in 1704; Jourdan's passage of the Rhine in 1795; Moreau's passage in 1796; the sieges of Kehl and Huninguen in 1797; Massena's passage of the Limmat, and Soult's passage of the Linth, in 1799; the passage of the Rhine, at Lucisteig in 1800; the passage of the Po, by the French, just before the battle of Marengo; and others in Italy, Germany, and Spain, in the subsequent campaigns of Napoleon.

Military bridges have sometimes been formed of ropes, cables stretched across the stream, and firmly attached at each end to trees, or posts let into the earth. If the shore is of rock, rings with staples let into the stone form the best means for securing the ends of the main ropes. Plank are laid on these cables to form the roadway. The ropes forming the "side-rail" of the bridge are passed over trestles at each shore, and then fastened as before. Short vertical ropes attach the main supports to these side ropes, in order that they may sustain a part of the weight passing over the bridge. Constructions of this character are fully described in Douglas's Essay on Military Bridges. For example, see the passage of the Po, near Casal, in 1515, by the Swiss; the bridge thrown over the Clain by Admiral Coligni, at the siege of Poitiers, in 1569; the operations of the Prince of Orange against Ghent and Bruges, in 1631; the passage of the Tagus, at Alcantara, in 1810, by the English; the bridge constructed across the Zezere, by the French, in 1810; the bridge thrown across the Scarpe, near Douai, in 1820; the experiments made at Fêre in 1823, &c.

The passage of a river in the presence of an enemy, whether acting offensively or in retreat, is an operation of great delicacy and danger. In either case the army is called upon to show the coolest and most determined courage, for its success will depend on its maintaining the strictest discipline and good order.

In the case of a retreat the bridge should be covered by field intrenchments, called a tête de pont, and defended by a strong guard. If the river be of moderate width, the enemy may be kept at a distance by heavy batteries on the opposite shore. As soon as the passage is effected by the main body, the bridge, if permanent, will be blown up, or otherwise destroyed by the miners, and if floating, will be swung round to the other shore. The rear-guard will pass over in rowboats, or the end pontons detached for that purpose. An army retreating in the face of an enemy should never rely upon one single bridge, no matter what may be its character: for the slightest accident happening to it might expose the whole army to inevitable destruction.

The passage of a river by main force, against an enterprising and active enemy on the opposite shore, is always an operation of the greatest difficulty, and not unfrequently accompanied with the most bloody results.

The most effectual method of accomplishing this object is by stratagem. Demonstrations are made at several points at the same time: bodies of troops are thrown across, after nightfall, in rowboats or by flying-bridges, to get possession of the opposite bank. The vanguard of light cavalry may cross by swimming. The pontoniers should have their bridge equipage in readiness near the intended point of passage, so that it can be thrown across with the greatest possible rapidity, while the advanced guards are still able to keep the enemy at a distance. Under favorable circumstances the pontoniers will have the bridge in readiness for the passage of the army before the enemy can collect his troops upon the threatened point.

Cannon-balls and hollow shot are the most effectual means for destroying an enemy's bridge when our batteries can be planted within reach. When this cannot be done, we must resort to fire-boats, floating rafts, &c., to accomplish our object. Operations of this kind carried on in the night, are most likely to succeed.

To protect bridges from the action of these floating bodies, stockades, or floating chevaux-de-frise are constructed across the stream at some distance above the bridge; strong cables, or chains stretched directly across the river, or with an angle up stream, may be used in place of stockades, or in conjunction with them. Guards should be stationed above the bridge, with boats, ropes, grapnels, &c., for the purpose of arresting all floating bodies and drawing thorn ashore, or directing them safely through the draw in the bridge arrangement.

The troops especially charged with the construction and management of the various kinds of military bridges, are denominated pontoniers. The duties of these troops are arduous and important, and, in a country like ours, intersected by numerous water-courses, the success of a campaign will often depend upon their skill and efficiency.

Sapping.—This is a general term applied to the operations of forming trenches, along which troops may approach a work without being exposed to the fire of the besieged.

In addition to the ordinary sapping-tools, such as shovels, picks, gabion-forks, &c., used in constructing trenches, there will also be required a considerable amount of sapping materials, such as gabions, fascines, sap-fagots, sandbags, &c.

The gabion is a cylindrical basket of twigs, about two feet in diameter, and some three feet in length, and without a bottom. It is made by driving into the ground, in a circular form, a number of small pickets about an inch in diameter, and of the length required for the gabion. Twigs are wattled between the pickets like ordinary basket-work, and fastened at the ends by withs or packthread. Gabions are used in forming saps, batteries, blindages, powder-magazines, and in revetting the steep slopes of field-works.

The fascine is a bundle of twigs closely bound up, from nine to twelve inches in diameter, and from ten to fifteen or twenty feet in length. The largest are sometimes called saucissons. In making a fascine, straight twigs about the thickness of a man's finger are laid side by side, and firmly compressed together by a strong rope or chain attached to the extremities of two levers. While held in this position the twigs are firmly bound together by withs or cords. Fascines are used in constructing trenches, batteries, &c., and for filling up wet ditches.

The sap-fagot is a strong fascine about ten inches in diameter and two feet in length, with a picket inserted through the middle. It is used in the double sap in connection with gabions.

Sand-bags are usually made of coarse canvass. When filled with earth they are some six or eight inches in diameter, and from eighteen inches to two feet in length. From their perishable nature, they are used only when other materials cannot be procured, and where it is important to place the troops speedily under cover from the enemy's fire.

Bales of wool, cotton, hay, straw, &c., may be employed in sapping for the same purposes as the above materials, when they can be procured in sufficient quantity. Pork and flour barrels, which are usually in abundance in a camp, are frequently filled with sand and used for forming magazines, blindages, &c., in field-works.

A trench constructed in ordinary soil beyond the range of the enemy's grape, is called a simple sap, or ordinary trench. The earth is thrown up on the side towards the place besieged, so as to form a kind of parapet to cover the men in the trench. The labor is here executed under the supervision of engineer soldiers, by working parties detached from the other arms. Fig. 50 represents a vertical section of a simple sap.

When within range of the enemy's grape, the flying sap is resorted to in order to place the workmen speedily under cover. In this operation, gabions are placed in juxtaposition on the side towards the besieged work, and filled with all possible speed by the workmen. Three rows of fascines are usually placed on the top of the gabions to increase the height. The most difficult part of the flying sap is executed by engineer troops, and the trench is completed by the ordinary working parties. Fig. 51 represents a section of this sap.

The full-sap is employed when the works of the besiegers are within range of musketry, or when the grape fire of the besieged is so deadly that the flying sap can no longer be used. This is a difficult operation, and unless executed with great care and by well-instructed engineer troops, the construction of the trench will be attended with an immense loss of life. The work must be executed under cover of a sap-roller, which is a cylindrical mass of fascines, wool, or cotton, some two feet in diameter. On very smooth ground a ball-proof shelter on wheels might be used as a substitute. The sap-roller being placed along the line of the trench so as to cover the sapper in front, who is armed with a musket-proof headpiece and cuirass, this sapper commences the sap by placing a gabion on the line of the proposed trench and fills it with earth, working on his hands and knees. Having filled the first gabion, he pushes forward the sap-roller and places a second one next the first, stopping the open joint between the two with a stop-fagot. The second gabion being filled in the same manner as the first, others are successively established. When the first sapper has advanced a few feet, he is followed by a second, also in defensive armor, who increases the excavation and embankment; this sapper is then followed in the same way by a third and a fourth, after which the trench will be sufficiently advanced to be turned over to the ordinary workmen. The sap-fagots may be removed when the embankment becomes thick enough to resist grape. Fig. 52 represents a plan and section of a full-sap.

When the direction of the trench is such that the men are exposed on both sides, it will be necessary to throw up an embankment both to the right and left. This operation is called the double sap, and is executed by two parties of sappers, working side by side. In this sap it will be necessary to frequently change the direction of the trench, or to throw up traverses, in order to cover the men at a distance from the sap-roller. Wing-traverses, on the side of the trench