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ART. VI. An Essay on the Principles and Construction of
Military Bridges and the Passages of Rivers in Military
It must be obvious to the common sense of every thinking
man, that an army destitute of bridge equipments, and unskilled in the art of putting them together, is, for all the practical operations of war, well nigh worthless. The infantry may
, be stout, sufficiently drilled and appointed — the cavalry horses good, and the artillery excellent — but, except for purposes absolutely and locally defensive, nothing whatever can be done with them. No general could move such an army, save along high roads or across open plains and commons; for the first river or canal which crossed the line of his march would interpose an insuperable obstacle to his further progress, and bring him to a stand-still. Accordingly we find that, as soon as nations pass
. beyond a state of absolute barbarism, they begin to devise means for surmounting this difficulty. The painted warrior is satisfied with his canoe or coracle. Carrying nothing with him except his weapons, on which he depends for his supplies in war, as he is accustomed to do for daily food in peace, he paddles over lakes and rivers in search of his enemy, or fees by the same process from him. But, no sooner has his tribe received the first rudiments of civilisation, than a different course becomes necessary. War has ceased to be an indulgence of personal revenge, or a struggle for the possession of some disputed hunting-ground. The objects sought by it are grander and more lasting. Our chief — now a king—is covetous of political power and extensive territory ; neither of which can be achieved except there be order and discipline in his masses. But order and discipline in masses are coincident only with such an extent of organisation as shall enable them when moving to keep together and to act in concert everywhere. The canoe and the coracle do not suffice for this, and if they did, they would still force our king to depend upon chance for the supply of his daily wants. He, therefore, takes to bridge-making; and the accounts which have come down to us of the military operations of the old Egyptians, Persians, Greeks, and Romans prove that he is not slow in arriving at a tolerable amount of proficiency in the art.
Darius laid his pontoons upon the Bosphorus and the Danube, and so passed them both. Let anybody read with
care the account given by Herodotus of the bridges thrown by Xerxes across the Hellespont, and he will be satisfied that there was no lack either of mind or of material in the Persian armies. So, also, we learn from Xenophon, that the broad Tigris failed to stay the retreat of the Ten Thousand, because they spanned it with a bridge upon thirty-seven trestles, and marched across. As to Alexander, it is evident from the statements of Arrian, that he carried to the conquest of India a bridge equipment as complete in every respect as any which at this day follows the track of the best appointed European armies. The passage of the Hydaspes fully settles this point. It was not effected at random, but by means of light vessels which were brought up upon carriages, divided, some of them into two, others into three parts, for the convenience of transport. These he put together on the river's bank, behind the screen of a thick wood, and having launched them, raft-wise - pretty much as our sappers and miners launched their rafts last summer on Virginia Water he marched his army across. Nor was the case different with the Romans, who seem to have carried this, as they did other branches of the art of war, to a high state of perfection. Cæsar informs us, that he was accustomed to pass the rivers of Gaul on wooden platforms, which were sustained at certain intervals by vessels made of wicker-work, and covered with the skins of beasts. And we need not pause to demonstrate, that the pile or
. tressel bridge which he laid upon the Rhine was as admirable a piece of military mechanism as any upon record.
The establishment of the empire did not, for many a day, affect injuriously either the skill or courage of the Romans. They continued to extend their conquests in all directions, neither the Danube nor the Euphrates, nor any other river arresting their progress; for they undertook no distant campaign with armies of which the equipment was not in every respect complete. And even when they fought only to keep what had been already won, they did it on scientific principles. The bridge-train of Julian, when he went forth to chastise the Persians, seems to have been excellent. It was the loss of this train, which, after the fall of Julian, compelled Jovian to capitulate on the banks of the Tigris to the Persian King Sapor. But a change comes over the vision of our dream, after the pride of Rome has been humbled, and her empire overthrown. A new age of barbarism arrives, and with it the neglect of all that has a tendency to redeem war (considered as an art) from its grossness. There was no more skill in manquvring men now —no more science in the preparation of means for facilitating the progress of columns from one point to another. Each feudal
VOL. XCVIII. NO. CC.
chief became the leader of a band of outlaws, working his will by sheer strength of hand, and incapable of surmounting any other difficulty than that which the person of a mailed adversary might present. How the leaders of the first crusade contrived to carry their followers through the east of Europe into the Holy Land we are unable to conceive.
But the enormous extent of their losses shows that every requisite to the efficiency of an army was wanting to them. Nor did matters greatly mend, as far as the particular art of which we are now speaking is concerned, for some time after the invention of gunpowder. The artillery first fabricated was of such unwieldly proportions that no bridges, except such as were composed of the most enduring materials, could sustain its weight. Indeed, so recently as the thirty years' war, the leaders on both sides were forced, in order to carry their guns across the German rivers, to bring up heavy oaken vessels ; from the floorings of which props sprang so strong that they sufficed to carry massive joists of timber, on which a road was laid. Bridges so formed, besides that they were extremely inconvenient of transport, ran a constant risk of destruction from the accidents of war or climate; for the carrying away of a single barge rendered all the others useless, and the means of repairing so serious a disaster were rarely at hand.
It was about the middle of the seventeenth century that the Dutch, first of modern European nations, began to adapt bateaux, or small vessels, to the formation of military bridges. These they prepared with very considerable skill. The sides were nearly vertical, the bottoms flat, the extremities gradually diminishing in breadth and terminating at each end in an inclined plane which made an angle of 45 degrees with the surface of the water. The vessels themselves were not of solid oak, but composed of a frame-work of timber over which a covering of tin was drawn. Hence their great portability, and hence also the application to them of the term ' ponton,' or 'pontoon, a word which has ever since been employed to signify a boat composed of light materials, and built exclusively for military purposes. The invention was so obviously valuable, that it soon attracted the notice of other States. The French followed the example of the Dutch so early as 1762, and supplied their armies with a regular bridge train, whch has never since been wanting to them. Other nations followed one by one a like course; so that early in the present century there was no army of continental Europe but numbered among its materials of war a bridge equipment. Some covered the frame-works of their pontoons with copper; some adhered to the Dutch model, and preferred tin; the Russians alone overlaid their wicker-work with sackcloth, which they saturated with tar till it became impermeable by water. But it does not appear that then, any more than now, pontoon bridges were considered adequate to all the emergencies of service. Marshal Turenne, for example, though carrying
one along with him, was afraid to trust his communications across the Rhine and the Meuse to materials so fragile. He formed his standing bridges out of the common country boats, and found them adequate. Nor can we be surprised at this. The pontoons in use during the war of the Spanish succession were much smaller than those to which we are accustomed; it was therefore necessary, in laying them down, to keep them closer to one another than is done in these days, because the bridge could not otherwise obtain buoyancy sufficient to support the weight of men, horses, guns and stores passing over; and as the course of the water was thus very much obstructed, the bridge, especially on rivers like the Rhine, ran great risk of being carried away by the current, besides incurring increased hazard of destruction from floating bodies sent down by the enemy from above.
Our next stage in the art of military bridge-making occurs about 1787 or 1788, when a M. Gribeauval, an officer in the French service, brought forward an improved pontoon, which was adopted and called after the name of the inventor. Its length was 36 feet 3 inches, its breadth 6 feet 9 inches, its height 3 feet 9 inches, and it weighed 4,079 lbs. avoirdupois. It was of vast capacity and buoyancy; for one such vessel, when used as a ferry-boat, could carry from fifty to sixty armed men across a river. But it laboured under this serious drawback, that its great weight rendered the task of conveying it from place to place difficult and laborious. One of the last occasions on which it seems to have been used was in 1809, when Napoleon supported upon pontoons of this description his bridge across the Danube. Its place has long ago been supplied in the French service by bateaux in every respect more convenient. We shall have occasion to describe them more in detail by-and-bye; but in the meanwhile our non-professional readers may not be displeased if we preface such description by a few general remarks explanatory of the nature of pontoon bridges in general, and of the manner in which they are prepared for the march, carried in the train of armies, and applied at the proper moment to their proper uses.
A pontoon bridge, then, is a road laid across or upon a river, of which the gangway is composed of planks, and the piers of buoyant vessels, fabricated after some approved model. Its constituent parts are the vessels in question, called pontoons, saddles, balks, chesses, and half-chesses. There are required to fix and manage it, saddle-lashings, rack-sticks, rack-lashings, breast-lines, outriggers, oars, boat-hooks, buoys, buoy-lines
, anchors, cables, body-lashings, carriage-lashings. All these materials are packed and carried about in waggons, so constructed as to receive their respective loads neatly, and to keep them while on the march secure. The numbers of waggons required in the team vary according to the extent of the bridge, and the manner in which its parts are distributed. But whatever the form of these parts may be, and however different the usages of each particular service in their distribution, they are all subject to one common contingency, - there must be car
riages, horses, and men set apart specially for their transport, otherwise their presence will operate as an incumbrance rather than as a convenience to an army.
Of the pontoon — the foundation, so to speak, of the bridge - it may suffice, at this early stage of our inquiry, to say that whatever be its shape, and the material of which it is formed, it is valuable in proportion as it unites in itself the various qualities of buoyancy, lightness. convenience of stowage, steadiness in the water, and applicability to purposes of navigation.
The saddle is a frame of fir timber, which, being placed centrally on the axis of a pontoon, is secured to it by lashings, and receives the ends of the balks.
The balks are small beams of fir, which rest on the saddles, and are secured in their places by iron bolts. They serve in the bridge the same purpose which joists do in house-building. They extend from one pontoon to another, and support the flooring or platform.
This flooring, or platform, is constructed with chesses, and half-chesses. The former consist of three fir planks a-piece, bound together in their breadth by four cleats, which fasten underneath; the latter are single planks, which, when the bridge is completed lie over the saddles, and can without difficulty be removed, whenever it becomes necessary to get at the pins or bolts which pass through the balks and keep them in their places.
With respect to the rest of the articles enumerated as belonging to the equipment of a pontoon bridge, their names, we presume, sufficiently set forth the purposes which they are intended to serve. Lashings of every kind, rack or twistingsticks, anchors, buoys, cables, boat-hooks, — these are implements with which our readers cannot but be familiar. If they desire to know exactly how and under what circumstances each is used, the best thing we can do for them is to advise, that