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Bible Encyclopedias
Military Bridging
1911 Encyclopedia Britannica
or "MILITARY BRIDGING ( see under Pontoon, 22.69). - At the beginning of the 10th century all the armies of the civilized Powers were equipped with pontoon trains of various forms. The European continental nations all had steel boat-shaped pontoons varying in size from the large German bipartite pontoon, which had about 8 tons effective buoyancy, to the Italian high-prowed pontoon specially suited for the swift current of the rivers in that country and capable of carrying lorries when two pontoons were placed stern to stern, and the French and Belgian pontoons, which were somewhat smaller than the British. The British army adhered to the bipartite wooden boat-shaped pontoon, 21 ft. over all in length, 5 ft. 3 in. beam, and 2 ft. 5 in. in depth, with a maximum effective buoyancy, when immersed to within 6 in. of the gunwale, of about 41 tons. The advantages of the wooden pontoon with waterproof canvas skin, as proved by the South African War, were lightness, quietness for night work, and the ease with which bullet holes could be plugged, or holes caused by shell splinters repaired. On the other hand, the steel pontoons undoubtedly stood the rough handling of active service better, and did not suffer like the wooden pontoons when they had to be stored in the open under a hot sun. They can also be more readily manufactured in large quantities in war-time, whilst the difficulty of obtaining a sufficient supply of thoroughly seasoned material greatly hampered the rapid expansion of the British bridging trains. Taking all considerations into account it seems probable that the next pontoons designed for the British army will be of galvanized steel, somewhat larger and appreciably deeper than the present pattern.
The British pontoons (as shown in fig. II) were made in two sections, the bow section having its gunwale rising towards the bow, and the body curved and tapered forward, so as to reduce the force of the current against the bridge. The stern section was rectangular in form, so that two pontoons could be coupled together stern to stern, or any number of sections could be coupled together to form rafts capable of bearing the weight of the heaviest gun carried in the field. Figure 12 shows the various uses to which the pontoon sections are put in forming light, medium, or heavy bridge. Normally when packed for travelling (as in fig. i 1) and when used in the normal form of light bridge designed to take a column of infantry in fours, field guns, and horse transport, the bow and stern sections were coupled together as one pontoon, which could be lifted off its carriage and launched by sixteen men gripping the handles at each side. The wagons carried also the superstructure of timber roadbearers (or " baulks "), which fit on the saddles of the pontoons to form the bridge, "chesses " or planks forming the roadway, and " ribands " or wheel-guides which hold the ends of the " chesses " secure and form the curb of the roadway. In addition to the pontoon wagons a bridging unit always included wagons carrying adjustable timber trestles known as " Weldon trestles." These were an important part of the equipment, being used to form the piers of the bridge in shallow water near the bank where the pontoons could not float, or to make a landing-stage when the pontoons were used as rafts on a wide river, or without the pontoons to bridge the narrow streams or dry gaps.
Light Bridge.
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'Medium Bridge. - 1 Saddle beams I Pontoons Lashed ¦ A Pontoon or '[[Longitudinal Section. Fig]]. 12.
In the organization of a British division of 1910-14 were included two, and in the division of 1915 three, " Field Companies Royal Engineers," each of which, besides its other military engineering equipment, included two pontoons and one trestle wagon, the latter carrying two trestles; the three wagons among them carried also five bays of superstructure for light bridge, using five baulks to a bay.' This gave every division the means of crossing a river independently, the engineers being able rapidly to form three bridges up to about 75 ft. in length, or one bridge of about 200 ft.; if used to form bridge of half-pontoons capable 1 The length of bridge section between two points of support technically called a " bay " is normally 15 ft.; thus a bridge supported on the two shore transoms, with piers formed of two pontoons and two trestles, would consist of five bays equal to a span of 75 ft. The width of the roadway of the bridge as normally formed is 9 ft. clear between ribands.
of carrying infantry in file and pack animals, the equipment could be extended to bridge about double this width.
Bridging trains moving in rear of the army carried each 42 pontoons and 16 trestles with superstructure, as a reserve for the crossing of wide rivers, and these were later supplemented with a superstructure of heavy steel joists, so that the pontoon equipment could be used to form medium and heavy bridges to carry mechanical transport and the heaviest guns and tractors on the road. The pontoon trains were originally drawn by horses, but to save the great number of horses a pontoon train requires, and to give greater mobility, some were adapted for mechanical transport. These consisted of " four-wheel-drive " lorries, each trailing two pontoon or trestle wagons, and were able on good roads to cover much greater distances in less time than the horse-drawn bridging trains.
The " Field Squadrons Royal Engineers " attached to cavalry divisions were equipped with a lighter form of collapsible boat, and each cavalry regiment was provided with an air-raft equipment. A special cavalry bridging train equipped with small steel pontoons was provided for use in Egypt and Palestine. These forms of bridging equipment could take the lighter natures of transport accompanying a cavalry brigade, including horse artillery guns.
On the other hand, the British army when it took the field in 1 9 14 had no reserve of heavy bridge equipment, nor any of the portable steel-girder bridges which were found so invaluable later in the war.
The British army, unlike most European armies, had no specialized bridging units. All the field units of the engineers carried out the annual course of bridging as part of their normal duty. This course was held wherever possible on the banks of a tidal river, and work was mainly concentrated on the pontoon drill which enabled the sappers to handle the material with great celerity. But the training also included practice with various forms of light improvised bridges, and the crossing of rivers by means of barrels, tarpaulin rafts, spar and timber trestles, and the construction of light suspension bridges. Little was done in the way of heavy bridging, but all units were taught the use of spars as derricks and sheers for launching girders and moving heavy loads, and a certain amount of pile-driving and heavy trestle work was done. The officers' theoretical course included the design of timber and steel girder bridges of all types, and some gained practical experience in bridging works in India and elsewhere abroad in the course of their employment in peace on the public works. Never, however, before the World War of 1914-8 had the problem to be solved been of such a varied and complex nature. The immense advance in the use of mechanical transport of all kinds, from motor-cars to steam traction engines, the greatly increased weight of artillery in the field, and finally the coming of the tank, demanded the use of heavy road bridges not far short of railway bridges in strength.
On the other hand, owing to the ease with which destruction can be carried out by means of modern explosives, advancing troops were more frequently than ever before confronted with the problem of crossing a river or canal when all existing bridges had been destroyed, approaches broken up by explosives, and the river and its environs defended by artillery and machine-gun fire. In such a case pontooning was clearly impracticable, and other means had to be devised by which the infantry could be given a footing on the opposite bank to form a bridge-head to cover regular bridging operations.
For these fighting bridges, which were practically the most important because without them no advance could be made, no standard equipment existed. Each field company improvised its own solution to the problem after reconnoitring the crossing to be forced. Usually the material could only be carted to within a mile or so of the site, and had to be carried by hand the remaining distance across shell-pitted ground, or marshland intersected by dykes. Lightness and extreme portability were thus essentials of the design. Then the material might suffer from shrapnel fire whilst en route or when lying hidden behind a bank or wall, and might be pierced by machine-gun bullets whilst actually Double chewed cleats Riban&t Saddle beam Nook bolt LJ Heavy Bridge.
?'L?? Pontoon baulks 3 Ribands alternately Pontoon Baulks å Ribands alternately. Hook bolt. /. Treble chessed r 9"- 3 cleat. Svddle beam. Thwarts.
Longitudinal Section.
being placed, hence strength and impermeability were required. Lastly, the bridge had to be put together in the dark in perfect silence, exposing as few sappers as possible on the bank, so that simplicity and interchangeability of parts were essential.
Strongly so that pack-animals can be got across with ammunition and supplies; these pack-bridges usually took the form of rough improvised trestle or pile bridges, but in some cases tarpaulins lashed round a wooden framing were used as floating supports in the same fashion as the waterproof sheets above mentioned.
  Note .-Framing about 5 x-Ys.Bottomsame form as B but wider. All Frames to be lashed together, not nailed 4 Carpenters 2%z hours per raft. '[[Plan ' 'Frame "A" Elevation]] ' -Handles slightly rounded /3x/0. Trench She/ter Side View I¦I Elevation Of -Groove for aura Cylinders binding - Saddle Beam 4 X 1;4 '6 ' 3 9`- Elevation Of Cork Floats e" - - Elevation Of Petrol Tins Fig. 13. The lightest and least vulnerable pattern evolved was probably the cork-float footbridge with light wooden footboards hooked over the saddles of the float and interlocking. A pattern of this type is shown in fig. 13, which also shows the employment of captured German canister floats and of petrol tins to support these light footbridges. A petrol-tin raft was used by the engineers of the British 25th Div. for the crossing of the Sambre-Oise canal near Landrecies in 1918; in this case each raft consisted of two floats each of eight petrol tins laid flat and built into a wooden crate for carriage. Eighty of these rafts were carried for 3,000 yd. under fire to the canal bank, and each when launched carried across a man with full equipment. When sufficient men had been ferried across by this means to secure a foothold on the far bank the rafts were connected by light footboards to form a bridge 55 ft. in length. A form of light ferry-boat which was very useful was made as shown in fig. 14 by tying the standard-size waterproof trench shelter, or bivouac sheet, measuring 13 ft. by io ft., over a light wooden framing made in parts for easy transport. In the little boat thus formed six men could squat, and be pulled across by a rope worked by a sapper who had swum to the far bank or paddled across in the first boat, another man on the near bank pulling the empty boat back; and considerable numbers of infantry could thus be put across even before a light footbridge could be constructed. The boats also formed a very serviceable footbridge when connected together as illustrated in fig. 3 (plate). In a case where a crossing could be effected at a canal lock or other point where the width to be spanned was not more than about 20 ft., a light trussed timber bridge was built up complete, and carried or rushed forward from undercover on wheels, and launched across the gap by the sappers, somewhat as a fireescape is handled. Similar devices have often been used in the storming of a fortress for the crossing of the ditch. A notable example of this method was the crossing at a lock on the Sambre-Oise canal made by the British 1st Div. on Nov. 4 1918. Another notable piece of front-line work was the construction of a crib causeway,' built of railway sleepers bolted together and sunk in the bed of the river, to carry tanks across the river Selle in the first line of the assaulting troops (1918). This was kept just below waterlevel for concealment, and was built in the nights just preceding the attack under the nose of the enemy holding the opposite bank. As soon as a foothold on the opposite bank has been gained by the infantry, and the enemy's machine-guns put out of action, the next step for the engineers is to establish the crossings more ? '0? - - ? I I s 2; 0, I Frame"8" Fig. For the crossing of minor streams and dykes often met with before or after the main crossing, various devices were used to suit the varying conditions. Plank or light footbridges of the pattern shown in fig. 13 were often sufficient to carry the infantry, but where the span exceeded to ft. light trussed bridges of timber, strutted and tied with hoop iron or stout wire, were made up to about 15 ft. in span. Above this limit some form of intermediate support in the form of a float or trestle became necessary. For marshland, muddy ravines, or shell-pitted ground, mats of canvas and wire netting stiffened with wood battens and rolled up for convenience of carriage were found very useful to give a foothold. For horse traffic, corduroy mats of timber bound together with wire and picketed down in place were used, as also were the artillery " trench bridges," 12 f t. in span with timber bearers and 12 in. flooring, made up in sections 3 ft. 6 in. wide to be laid side by side. These were a little heavy for hand carriage; but in most cases they were issued to the artillery before the advance and carried by them in their limbers to be laid down where required. Next, it becomes necessary to bring forward the field artillery into position on the far bank. For this work the pontoon equipment is invaluable, as it enables a bridge for horse transport to be made across a river more quickly than it is possible by any other means, and the peace training of the British engineers in pontooning work justified itself in the fine work done, notably in the advance across the Aisne in Sept. 1914. The field companies of the New Army were likewise instructed in and equipped for pontooning work, and the material was used to advantage on nearly every waterway on the entire front in France, on the Piave, on the rivers of Palestine, and in Mesopotamia.
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