! '^ ^'h'Vdfr''HftiflrlS!4WS GE EQUIPAGE r (^0vm\l W^mmmi^ Jitotg THE GIFT OF \y\ I Jqi • -^'^-MyWV' .O' j^irT^t^u^xw^^^ UG 335.U58"" """"""* "*"^ °'^'?iJniNiiiii!i]iSiiiifi'* '•"''fl* equipage of t 3 1924 026 074 231 Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924026074231 OEGANIZATION OF THE BRIDGE EQUIPAGE UNITED STATES ARMY, WITH D1EECTI0N8 FOE THE CONSTRUCTION OF MILITARY BRIDGES. PREPARED BY A BOARD OF ENGINEER OFFICERS, WASHINGTON : GOVERNMENT FEINTING OFFICE. 1870. Eepwnted, 1898. ^^3^ ^ F lo — Office op the Chief of Engineebs, United States Army, Washington, June 15, 1898. Sir: I have the honor to recommend that 500 copies of " System of Bridge Equipage and Directions for its Manoeuvre," with illustrations, prepared under the orders of the Chief of Engineers by a Board of Engineer Ofi&cers in 1869, and, with the approval of the Secretary of War, determined and estab- lished for the Engineer Service of the Army, be reprinted at the Government Printing Office, upon the usual requisition, for the use of this office, for distribution to engineer officers in the field. This manual is a necessity in connection with the use of ponton trains, and there is a great demand for it. The former edition is entirely exhausted. Very respectfully, your obedient servant, John M. Wilson, Brig.- Gen. Chief of Engineers, TJ. (S. Army. Hon. E. A. Algeb, Secretary of War. Approved. E. A. AEGER, Secretary of War. GEN. ORDERS, ) HEADQUARTERS OORPS OF ENGINEERS, No 6. ) Washington, D. C, Nov. 15, 1869. The following system oi Bridge Hquipage and Directions for. its Manoeuvre, -pveTpared under the orders of the Chief of Engi- neers by a Board of Engineer Officers, is, with the approval of the Secretary of War, hereby determined and established for the Engineer Service of the Army. A. A. Humphreys, Brig. Gen. and Chief of Engineers^ 3 WiLLETS Point, New York, Engineer Depot, June 30, 1869. Brig, and Bvt. Maj. Gen. A. A. Humphreys, Commanding Corps of Engineers. General : The Engineer Board convened by Special Orders, No. 168, dated Headquarters Corps of Engineers, December 19, 1868, has the honor to submit the following report on the construction and organization of bridge trains for the armies of the United States, and on the methods of constructing mil- itary bridges of all kinds, with or without the bridge equi- page — including a complete manual for the instruction and drill of pontoniers. Very respectfully, your obedient servants, J. 0. DUANB, Lieut. Col. of Engineers and Bvt. Brig. Gen. Henry L. Abbot, Major of Engineers and Bvt. Brig. Gen. William E. Merrill, Major of Engineers and Brevet Colonel. OOKTENTS. Page. ISTEODUCTION 9 CHAPTER I Passase of Eiveks. Passage: By fords; upon icei by boats, rafts, etc.; by bridges. Preserration of bridges 17 CHAPTEE II The Beidqe Equipage. Eeserve Equipage: Organization; bridge material; carriages and tbeir loading; tabular summary 25 Advance-Guard Equipage: Organization; bridge material; carriages and their loading; tabular summary 32 Peksonmel 36 CHAPTEE m.— Boat Manceuvbes. School of the Pontonier 37 School of the Boat; To embark; simple exercises; to turn the boat rapidly; to moTO sideways ; to cast anchor; to weigh anchor; to debark; to salute 40 School of the Flotilla: To embark; evolutions of a flotilla; to anchor the flo- tilla; to weigh anchor; to dehark 43 Febbiage of Troops: Infantry; cavalry 52 Eerbiage of Material: Army supplies ; guns; pontou trains 55 CHAPTEE IV Bridges with the Bridge Equipage. Bridge by Sucoessivb Pontons : Method of construction ; to dismantle the bridge. . 58 Bridge by Pabts : Method of construction ; method of dismantling 62 Bbidge BY Eafts 63 Bridge BY Conversion : Method of construction ; method of dismantling 63 General Remarks on Ponton Bridges : Comparison of the four methods ; draw in the bridge; the abutment bay; bridge with extended intervals 65 Bridges with Advance-Guard Equipage i 68 Number of Pontoniers Eequibed 69 Trestle Bbidgbs: Trestle bridge on land; trestle bridge over a water-course 70 Ponton Drill: To construct a bridge by successive pontons ; to dismantle abridge by successive pontons ; loading the ponton on the wagon; to construct a trestle bridge on land ; to dismantle a trestle bridge on land ; trestle bridge over a water- course 72 Expedients WITH Insufficient Trains: Elying bridge; trail bridge; rope ferry; prairie raft; bridges from boats of commerce; timber raft; raft of casks; tem- porary trestles ; pile bridges 81 Preservation of Bridges 91 CHAPTEE v.— Bridges without the Bridge Equipage. Trestle Bridges for Eailways : The trestle ; to raise a trestle ; connection of track and trestles; longitudinal bracing; cross-ties and guard rails ; temporary trestles as scaffolding for trusses ; ice-breakers; pile foundations ; load on railway bridge. 93 Strength of Tbgstle Bridges: Strength of posts; strength of caps; to compute the bridge dimensions ; bracing of trestle bridges , 98 7 LIST OF PLATES. Plate I.— Tbestle. II. —Ponton, Eeseeve Train, III.— POKTON CAKEIAGE, EeSERVE TRAIN. IV.— Details of Ponton Carriage. V Details of Ponton Careiaqe. VI.— Chess Wagon, and Ponton Waoon Loaded with Trestle. VII. — Details of Chess Wagon. VIII.— Ponton, Advance-Guaed Teain. IX.— Load of Ponton and Trestle Wagon, Advance-Goaed Train. X.— Tool Wagon. XI Construction op Ponton Bridges. XII.— The Ablttmbnt Bay, Extended Intervals, Ponton Lashings. XIII.— Trestle Bridges. XIV Plying Bridges, Trail Bridges, Eope Feeet. XV.— Loading Ponton Cabhiage, Ilmber and Cask Eafts, Peairie Raft. XVI.— Pile Bridges. XVII.— Chattanooga Plying Bridge. XVIII.— Railway Trestle Bridges. Note. — These plates, contaiued in a separate atlas, are drawn upon a sufficiently large scale to serve for working drawings. Copies of those especially needed in the instruction of engineer troops, (Plates XI to XVI, inclusive,) reduced to half -size liy the photo-litho- graphic process, are bound in this volume. INTRODUOTIOE The followiug brief history of the steps which have been taken, in this country, to organize a bridge equipage adapted to our service, will sufficiently explain the reasons that have induced the Board to recommend the system described in the following report. Previous to the Mexican war, no attempt was made to organ- ize a bridge equipage in our service. During this war, two com- plete trains of india-rubber pontons were constructed and sent into the field. At Its close these trains were sent to West Point, where they were used for the instruction of cadets and engineer troops. A full description of this equipage is given in the "Professional Papers, Corps of Engineers, Xo. 4." It soon became evident that india-rubber was not at all adapted to the construction of pontons — First. From the perishable nature of the material. Thecyl- inderKS are formed of alternate layers of canvas and india-rub- ber. The sulphur used in the process of vulcanization gener- ates sulphuric acid, which soon destroys the fabric of the cloth. Second. The extreme elasticity of this species of support gives to the bridge a rocking and oscillating motion, so violent as to render it unsafe for the passage of animals. Third. The most serious objection, however, is that a punc- ture, either above or below the water-line, is equally fatal to the cylinder. Hence, a single sharpshooter, from a rifle-pit on the enemy's side of the stream, can destroy these pontons as fast as they are launched. In the autumn of 1858 the india-rubber pontons having be- come entirely unserviceable, experiments were made to deter- mine the composition of a bridge equipage that should be adapted to our service. In conducting these experiments, the following fundamental rules were kept constantly in view : First. The mobility of the train must be such as to enable it 9 10 INTRODUCTORY HISTORY OF to keep pace with all the movements of the column to which it is attached. Second. Tlie train should furnish the means of ferrying troops promptly and safely, as in the case of disembarkations and the passage of a river by force. Third. It should furnish the means of constructing a bridge capable of passing an army with all its trains over th(i largest and most rapid rivers, with safety and without delay. Now, under the most favorable circumstances, it is very diffi- cult to reconcile the first and third of these rules, when but one species of ponton is employed. In this country it is impos- sible. The immense trains with which our armies are unavoid- ably encumbered, the long marches to be made, and the nu- merous wide and rapid rivers to be crossed, demand an equi- page of the most substantial character. On the other hand, the extended expeditions of light columns, which necessarily at- tend our military operations, require a train light enough to keep pace with the most rapid cavalry movements. Hence we require both a reserve and advance guard train. The experiments above named included the trial of samples of the bridge equipages used by those European armies most experienced in the art of military bridge-building. Pontons were constructed after the models of the French bateau, the Austrian sectional ponton, and the Eussian can- vas boat. Oorrugated-iron boats were procured, corresponding as nearly in form and dimensions to the French and Austrian boats as the nature of the material would permit. A number of Birago trestles were also constructed. All of the above material, with the exception of the iron boats, was prepared by the enlisted men of Company A, Engineers. The bridges formed of this material were exposed as much as possible to the action of heavy loads, storms, the tide, and floating ice. The material was also packed on carriages of various patterns in order to ascertain the best form, both of bridge material and of carriage, for transportation. The selection of the French, Eussian, and Austrian trains for these experiments, was made after a careful study of the various equipages used at present by the armies of Europe. These three nations alone appeared to have definitely settled on their systems, and this after much experience and thorough research. The Prussians and Spaniards were seeking for substitutes for 'J HE U. S. BRIDGE EQUIPAGE. 11 their bridges, which liad proved unsatisfactory. The Sardin- ians had adopted a plan inferior to that of the Austrians, though similar in some respects. The English tin ponton had too many of the defects of the india-rubber to answer our purposes. After experimenting for two years with the above-mentioned material, the following conclusions were reached: The French ponton is superior to the Austrian in simplicity and stiffness; as a ferry-boat, it will transport more troops and is more easily managed; in the bridge its superiority is marked. With the French equipage, the corresponding ba-lks of the adjacent bays lap each other about six feet, and are firmly lashed together and to both gunwales of the ponton, which greatly increases the strength and stift'uess of the roadway ; while with the Austrian, the balks must meet on a sill directly over the axis of the boat. The bays thus hinging on this sill, full jjlay is allowed to the horizontal and vertical oscillation to which floating bridges are subject. As to laud transportation, the French train requires fewer carriages to transport the same length of bridge than the Aus- trian, since for each section of the latter ponton a separate ve- hicle is necessary. The length of the two carriages does not differ materially, this being determined by the length of the balks. These considerations led to the adoption of the French ponton. The next question was, what material should be emi)loyed in its construction. Lifeboats having been successfully manu- factured in this country out of corrugated iron, it was pre- sumed that this material could be used with equal advantage in the present case. The iirst boat, made of the same thick- ness of metal as the largest class lifeboat, jiroved to be defi- cient in stiffness when placed in the bridge. The corrugations, running from bow to stern, diminished the power of the sides to resist the vertical strain caused by the weight of the road- way on the gunwales. To remedy this defect, it was proposed to line the boat amidships with iron corrugated vertically or to introduce strong iron ribs. These expedients, though they would have increased the weight beyond that of the wooden ponton, might have been suc- cessful, but they were not attempted, as the boat failed in other respects. In fact, it would not bear land transportation ; as, in 12 INTEODUCTOBY HISTORY OF travelling over a rough road, the joints open, either the rivets or sheet iron giving way. When in the bridge, if the boat grounds on an uneven or rocky bottom, a hole is frequently punched through it, and such injuries can not be repaired in the field. The wooden ponton is not only much less liable to such accidents, but can be readily repaired when they do occur. Previous to the battle of Gettysburg, a ponton bridge over the Potomac at Harper's Perry was destroyed, the ponton being scuttled and set adrift above the rapids. About three weeks after, the water having fallen, the boats were recovered, re- paired with pieces of hard-bread boxes obtained from the com- missary, and used in constructing a bridge at Berlin, over which the entire Army passed into Virginia. With regard to the canvas boat, it soon became apparent that it was precisely what we required for our advance-guard train. It is light, simple, strong, easily repaired, and when packed can safely be transported with the superstructure of the bridge as rapidly as any column of troops can move. A strong argument in favor of its adoption was that it had been used successfully by the Russians for more than a hundred years, under every variety of circumstances likely to occur in this country. The selection of the carriage for transporting the bridge ma- terial was next taken up. The Pvench ponton wagon is not adapted to our rough roads. The wheels are too small, and can not be increased in diameter without raising the load too high above the ground. A carriage was finally devised on the principle of the four- horse truck used in the city of Kew York. By means of the horizontal fifth wheel over the front axle, and of an inclined wagon bed, forward wheels of the requisite size were enabled to reverse completely under the load, thus allowing the car- riage to turn in a short space. This construction is absolutely necessary when so long-geared wagons travel over a crooked road. For the chess wagons and canvas train, a similar wagon would, without doubt, have answered the purpose perfectly, so far as transportation was concerned; but the ordinary baggage wagon of the Quartermaster Department, with some modifica- tions, was used on account of the facility with which it could be obtained and the readiness with which spare parts could be procured for repairs in the field. The Birago trestle, which had been recently adopted by most THE TJ. S. BEIDGB EQUIPAGE. 13 of the European nations, was also thoroughly tested ; and, the result proving favorable, it was proposed to employ it in con- nection with the pontons of both trains. .From the information gained by these experiments, there re- sulted the system of bridge equipage adopted at the commence- ment of the late war. During the winter of 1861-62, five trains were constructed, each composed of thirty-four pontons and eight trestles — the pontons being nearly of the same form and dimensions as the French bateau. The frame was some- what different, the ribs being entire and strongly ironed, and the ironing stronger throughout. The stern was provided with a locker. There were also other alterations in the details of construction. The balks were stronger; and the Birago trestle was modified [hj substituting built beams, instead of solid timber, for the trestle caps and balks. At the same time several canvas trains were organized. In constructing the ponton frame, the dimensions and form of the Russian boat were exactly retained. The scantling for the frame was considerably lighter, but, being strongly braced and ironed, the strength was about the same. One train was composed of canvas boats and trestles; being, in truth, a trestle train, with auxiliary pontons to be used only where the depth of water, or jnuddy bottom, prevent the use of trestles. In the month of February, 1862, a p6nton bridge, composed of about sixty boats of the reserve train, was thrown across the Potomac at Harper's Ferry. The river was then a perfect tor- rent, the water being fifteen feet above the summer level, and filled with drift-wood and floating ice. The greatest difficulty was experienced in pulling the pontons into position, and it was necessary to make use of ship anchors and chain cables to hold them in place. Notwithstanding these unfavorable cir- cumstances, the bridge was completed in about eight hours, and the corps commanded by General Banks, with all its trains and artillery, passed over it without accident or delay. Several of these trains accompanied the Army in the Penin- sular campaign. The pontons were used in discharging quar- termaster and commissary stores at Ship Point; in disembark- ing General Franklin's command at West Point; and in con- structing bridges over Hampton Greek, the streams in front of Yorktown, and the Upper Ohickahominy. Finally, a bridge was built over the Lower Ohickahominy, about two thousand feet long, over which nearly the whole army of the Potomac, 14 " INTEODUOTOEY HISTOEY OF with its immense trains, artillery, and cavalry, passed with promptness and safety. After the army had passed, the bridge was dismantled and the balks, chess, etc., packed into the pontons, which were formed into rafts and towed by steamers to Washington. The bridge trains were next transported to Harper's Ferry, where a bridge was constructed a second time, bat under entirely different circumstances from that built during the previous winter. The water was now not deep enough ; and, as it con- tinued to subside shortly after the bridge was laid, many of the pontons grounded on a very uneven and rocky bottom. Some of them were completely out of water, yet the heavy trains continued to move over the bridge without seriously in- juring them ; and when the water rose, most of them floated as well as ever. Discovering in this way that the boats were much stronger than we had supposed, we were enabled to imj^rove the method of bridging tidal streams. It had formerly been considered necessary to build out to low-water mark with trestles, so that the ponton should always be afloat. The bridge is now commenced at high-water mark, building with pontons alone. As the water subsides, the pontons nearest shore ground successively, forming a gentle ramp from the abutment to the floating portion ot the bridge, instead of making the descent in twenty feet, as formerly. This method, of course, applies only to -wooden pontons, and to cases where the bottom is favorable. During the Fredericksburg campaign, it became necessary to force the passage of the Eappahannock. The enemy having entrenched themselves on the bank, prevented for some time the construction of the bridge; until, at length, troops were embarked in the pontons and ferried across, where they stormed the rifle-pits and held them until the bridge was completed. During the year 1863 the ponton trains accompanied the army in all its marches backward and forward through Virginia, frequently bridging the Potomac, Rapidan, andHappahannock. In the latter stream the bridges remained in position all winter, and, notwithstanding the frequent floods and the quantity of ice formed, but few interruptions occurred upon these thorough- fares. During the campaign of 1864 trains composed of fourteen I)ontons and two trestles accompanied each of the three army THE U. S. BRIDGE EQUIPAGE. 15 corps of the Army of tbe Potomac. These trains attended their corps iu the long march from Culpeper to the James Elver J and, although the roads were frequently very bad, in no instance did they delay the march of the troops or arrive late when a bridge was to be laid. The headquarters train was followed by a canvas train, which, when a crossing was to be made by surprise, was sent forward with the cavalry, who covered the construction of the bridge and held the position till the main body arrived. On reaching the James Eiver, a bridge was laid, opposite Charles City Oourt-House, about two thousand feet in length. The water was so deep and rapid that the pontons could not be held by their own anchors, and it was found necessary to attach their cables to schooners anchored above and below the bridge. Thus the wooden jjonton train, through four years of war during which the bridges constructed were without parallel in number and magnitude, amply fulfilled all the requisites of a good bridge equipage. The frequent crossing of the Chicka- hominy, Potomac, and James rivers proved that, even under tbe most unfavorable circumstances, it could furnish a bridge capable of passing a large army with its heaviest trains over wide and rapid streams with safety and despatch. Its capabilities in ferrying troops were shown at Ship Point, West Point, and Fredericksburg; and of the mobility of the equipage there was abundant proof in the long marches during the last two years of the war. The canvas equipage, also, was perfectly successful as an advance-guard train. In the cavalry raids it was always able to keep pace with the columns; and, although they frequently marched hundreds of miles, it was invariably ready to furnish a prompt and secure means of crossing all the streams on their route. It also often furnished bridges for the heavy trains of the army over streams of moderate width and rapidity. The only part of the bridge equipage which did not realize all our expectations was the Birago trestle. As already stated, a train was organized early in the war on the Austrian principle, in which the trestle is the main depend- ence, the ponton being merely auxiliary. It was supposed that many streams would be encountered which could be bridged best with trestles alone, but none such were met with. In fact, when a stream is more than two feet deep, a ponton bridge may be 16 INTEODUCTORY HISTORY. laid ; when less than that depth, if the bottom is hard, it may be forded and. no bridge is required; should the bottom be solt, the trestle legs will usually settle so as to render the bridge unsafe. As it was not deemed advisable to transport with the army a train which could only be used in exceptional cases, this description of equipage was abandoned. The trestle was, however, very useful as an auxiliary, especially with the canvas train; for, as these boats when in the bridge should never be allowed to touch the bottom, it is frequently necessary to build out several bays from the shore before sufficient depth of water can be obtained to float the ponton — and for this purpose nothing could be better than the Birago trestle, which is also equally useful for a similar purpose with the reserve train, when the river bottom is rough near the shore. The canvas train was extensively used by the Western army, and with such success that it was proposed to employ it ex- clusively. Experience, however, in the East has clearly proved that this train cannot fulfil all that is required of the bridge equipage of a large army. The bridges of the Potomac and James rivers could not have been built with canvas boats, which will not resist ice and driftwood; neither are they suited to the disembarkation of troops or the passage of a river by force. Experience would therefore lead us to concur with General Barnard in his remarks on this subject, viz : "The numerous proposers of 'flying' bridges forget that if a military bridge is intended to be carried ivith an army it is also intended to cm-ry an army, its columns of men, its cavalry, its countless heavy wagons, and its ponderous artillery. It must carry all these, and it must do it with certainty and safety, even though a demoralized corps should rush upon it in throngs. "IS'o make-shift expedient, no 'ingenious' invention not tested by severe experiment, no light affair of which the chief merit alleged is that it is light, -will be likely to do what is required, and what the French ponton has so often done." CHAPTEE I. PASSAGE OF RIVERS. When an army in the field finds its march interrupted by a river, it may effect the passage of this obstacle either by ford- ing, by ferrying in boats, rafts, or flying bridges, or by military bridges. The selection of the place and means of crossing a river is determined by a reconnaissance, which should be as detailed and extensive as circumstances will permit. By fords. — A river with a moderate current may be forded by infantry when its depth does not exceed three feet, and by cavalry and carriages when its depth is about four feet. The requisites for a good ford are, that the banks are low but not marshy, that the water attains its greatest depth gradually, that the current is moderate and the stream not subject to freshets, and that the bottom is even, hard, and tenacious. In mountainous countries the bottom is frequently covered with large stones, rendering the passage of carriages nearly or quite impracticable. In level countries the case is often still worse, the bottom either of mud or quicksand being impassable for both men and carriages. Sometimes the bottom is composed of fine sand which is hard enough, but which by the action of the hoofs of animals is stirred up and washed away, increasing the depth until the stream becomes unfordable. The best bottom is coarse gravel. Fords are usually found in the wider and more rapid parts of the river. Their position may be determined by sending a number of mounted men across wherever there is a probability of the river being shallow enough. The most certain method is to float down the stream in a boat, keeping it in the swiftest part of the current, where the stream is usually the deepest. Over the stern a sounding line of the proper length is hung; when this touches bottom the river is sounded across. When the ford is discovered, the remarkable objects on the 21638 2 IV 18 PASSAGE OF RIVERS shore should be noted, that the place may be easily recognized; and a picket should be planted at the water's edge, in order that any variation in its height may be ascertained. Eivers which are not fordable may sometimes be rendered so, when the only obstacle is a too great depth of water over an extent of eight or ten yards, by filling in this portion of their bed with fascines loaded with stones, or with stone and gravel. When the water is sluggish or muddy, a ford may be im- proved by covering the bottom with bundles of coarse grass, rusLes, or twigs. There have been iustances of rivers rendered fordable by diverting a jjortion of the water from its natural course. When the stream is wide and rapid, the ford must first be carefully examined and staked out. The troops pass in column, with sufficient intervals to avoid choking the current. When boats are to be had, a few should be stationed below the ford to assist men who may be carried down by the current. When boats are wanting, this duty may be performed by mounted men, or a life-line may be stretched across, supported on casks or other floats. The force of the current may be broken, in a measure, by stationing cavalry in the stream just above the point of crossing. After a freshet the ford should be reexamined, lest some alteration may have taken place in the bed of the river. In marching in retreat it is frequently advisable to destroy a ford after having used it. This may be eflf'ected by digging trenches across it, or filling in the deepest part with harrows, teeth up, planks filled with spiks, crow's feet, etc. Upon ice. — In high latitudes, during the winter, rivers are frequently covered with ice of sufficient thickness to sustain the heaviest loads. This means of communication should be used with great circumspection. A change of temperature may not only suddenly destroy this natural bridge, but render the river impassable by any method for a considerable time, in consequence of the floating ice. The thickness of ice should be, to allow the passage of infantry in single file on a line of planks, and two yards apart, two inches; cavalry, or light guns, with intervals, four inches; 12-pounder field-pieces, unlimbered and on sleds, five inches ; 12-pounder field-pieces, limbered and drawn by horses with intervals between pieces, six to seven inches. Ice when ten to twelve inches thick bears the heaviest loads. 19 Two tracks of planks laid on the ice for the carriagewheels to run on, may be emjjloyed when there is any doubt as to its strength, or the wagon may be transformed into a sort of sled by fastening two planks under the wheels. The thickness of the ice maybe increased, when thetemperi- ature is low enough, by throwing water on it. When the river is frozen on each side, but open in the middle in consequence of the velocity of the current, a boom stretched across the open space will often check the velocity sufficiently to cause the water to freeze. Passage on boats, rafts, etc. — The point of passage being selected, all the boats that can be procured will be collected. In default of a sufficient number of them, lumber, casks, and other material suitable for rafts, should be procured, and the rafts be constructed without delay. The banks, if too steep, will be cut down; the landing on the opposite shore should be further down the stream than the point of embarkation, as the loaded boats will drift with the current. The boats will be arranged along the shore according to size, and numbered; the rafts should be moored below the boats. The infantry will be divided into sections, depending in size upon the capacity of the boats in which they are to embark; each section will be provided with the number of its boat; great care must be taken not to overload the boats or to crowd the boatmen. The soldiers will enter the boats one by one, alternately against the right and left gunwale; they will be cautioned not to stir from the places assigned them, and above all not to spring up when the boat lurches ; they will disembark in the same order, i. e., one by one. When the river is shallow near the shore, the boat must not approach the bank near enough to ground as the men file in. In the passage of artillery it is usually necessary to dismount the piece. Horses are not often passed over in boats, since they may usually be more conveniently made to swim. When boats of sufficient size are available, their bottoms must be covered over with plank, and the horses be placed crosswise, facing alter- nately up and down stream; otherwise they may be thrown down by the rolling of the boat. Bafts. — The passage of all arms may be facilitated by con- 20 PASSAGE OF EIVEKS structing a floating bridge, formed of two boats covered with a platform constructed as follows : From five to seven beams of the same thickness are laid across the two boats, the interval between the beams being equal, and such that the covering j)lank8 extend one foot beyond the extreme beams. The interval between the boats is such as to allow the beams to extend two feet beyond the outer gunwales. The beams are lashed to the boats ; the covering planks are kept in place by two side-rails laid directly over the outer beams and lashed down to them; the extreme planks are nailed down. The size of the beams is regulated by the load, and the interval between the boats. With seven beams twenty-seven feet long and five inches square, and covering-plank one and a half inch thick, a 24-pounder may be carried. Not only may artillery and cavalry be transported by this means, but also infantry in much greater numbers than by using the boats separately. The floating bridge can be manoeuvred by oars with nearly the same facility as a boat. The same rules apply to the passage of troops on rafts as in boats, attention being paid to the following circumstances : that rafts drift more than boats, consequently the landing on the opposite shore will be further downstream; and that, as the embarkation is easier, there is more danger of overloading the raft and of confusion in embarking. Infantry enter by the flank and occupy first the middle of the raft, through its entire length; a rank is then added alternately on the up and down stream side until the raft is loaded. Artillery and heavy carriages are placed in the centre, and cavalry as in the boats. Eafts possess these advantages over boats, viz: the embar- kation and landing of all arms are easier; they carry large numbers at each trip; they are not easily injured by the fire of the enemy ; they draw little water. They cannot, however, be navigated with the same facility as boats, and move much more slowly through the water, thus keeping the troops a longer time under fire when in the pres- ence of an enemy. They cannot be directed with certainty on a fixed point when the stream is rapid, and in this case it is often impossible to bring them back against the current to the starting point. BY BOATS, EAFTS, ETC. 21 Finally, the length of time required for their construction forbids their use when the passage is to be effected secretly. When the material is limited in quantity, the passage will be executed more readily by means of the rope ferry, trail or fly- ing bridge. The rope ferry, which is used in streams with sluggish cur- rents, consists of a floating support, either raft, floating bridge (as described above), or a wide scow. It is drawn by hand along a rope stretched from bank to bank. The trail bridge is employed on streams of not more than one hundred and iifty yards in width, and with a current whose velocity is not less than one yard per second. The rope must be maintained above the surface of the water, and consequently must be drawn very tight by means of windlass, blocks and falls, or similar expedients; it must also be raised at each bank some distance above the water. The raft or boat is attached to a pulley which runs on a sheer line, and by means of a rudder is given such a position that its side makes an angle of about 55° with the direction of the current. The force of the current exerted on the side of the float may be divided into two components, one perpendicular to the sheer line, which is destroyed by the resistance of this line, the other parallel to it, which causes the float to cross the stream with a velocity depending upon the strength of the current. The most suitable float for the purpose is one composed of two long, narrow, and deep boats, with nearly vertical sides. The interval between the boats is such that the current shall act on the sides of both through their entire length, when they form the proper angle with it. When timber rafts are used they should have the form of a lozenge, whose acute angle is 55°. When two sides are parallel to the current, the up stream side will then be in the most favorable position for the passage. Flying bridge. — When the river is more than one hundred and fifty yards in width, the strain on the sheer line would be very great; it is, therefore, usually replaced by a cable, one end of which is attached to the float and the other anchored in the stream, thus forming a flying bridge. The cable is supported by several floats, either small boats or barrels, logs, etc. When an anchor is used, the first float should be as near it as 22 PASSAGE OP RIVEES. possible without danger of tripping it; the others should be so arranged as to maintain the cable above the water. The cable is anchored in the middle of the stream when the cur- rent is stronger there; but when stronger near one shore, it must be anchored nearer the other. If no floats for the cable are used, it must be jiassed over a gallows frame on the raft to keep it from dragging in the water. The flying bridge is manoeuvred in the same manner as the trail bridge. Eope ferries or trail or flying bridges furnish the means of passing any stream, and may be advantageously employed in many cases. They may be established without difQculty in a short time, and with limited material such as can often be found in the vicinity. They permit the passage of all arms aiud of the heaviest loads. They are not liable to injury from floating bodies, and the flying bridge does not interrupt navi- gation. By bridges. — When a river is more than four feet in depth, or when its bottom is of mud or quiclisaud, recourse must be had either to ferrying by means of boats, rafts, etc., or to mili- tary bridges. The latter are always to be preferred when circumstances will permit their establishment. Military bridges are composed of a roadway and its sup- ports; the first consists of beams or balks reaching across the adjacent supports, and covered with plank called chess. The supports, from which the bridge takes its name, may be either fixed, as trestle, gabions, carriages, piles; or floating, as pontons, boats of commerce, rafts, etc. Ponton bridges are preferable to all others when a passage by main force or surprise is to be undertaken. They may be constructed on any stream of suf&cient depth. Pontons may be replaced by rafts when the velocity of the stream does not exceed six feet per second. In swifter cur- rents the latter are unmanageable, drag their anchors, and are liable to destruction from floating bodies. Trestle bridges may be constructed in rivers whose depth does not exceed nine feet, and whose velocity is not more than six feet. They may be employed with advantage in rivers of moderate depth and gentle current, with hard, even bottoms. When the bed of the river is uneven, the adjustment of the trestles to the bottom is very tedious, and, if the current is PRESERVATION OF BRIDGES. 23 rapid, almost impossible. When the bed is of mud or fine sand, the settlement of the legs is liable to be irregular. Gabion bridges are used over marshes and shallow streams.. They consist of gabions constructed in the ordinary way, and of a height necessary to give a level road; these are placed in rows perpendicular to the axis of the bridge, are filled with stones or gravel, and are capped with a piece of timber on which the balks rest. Pile bridges are superior in point of stability to all other military bridges, but, requiring much labor and" time in their construction, they are usually restricted to securing the com- munications in rear of the army. Preservation of bridges. — Military bridges being merely temporary expedients, the same solidity is not required in them as in permanent bridges. It is sufincient to give them the strength required to support the weight of the heaviest loads which accompany an army, and to resist the action of the current, which has a tendency to tear away the supports. The first requisite is attained by giving sufficient volume to the supports if they are floating, and sufficient vertical strength if fixed, and by using balks and chess of the proper dimensions to correspond with their length between bearings. To resist the action of the stream, a good system of anchor- age, the greatest possible distance between supports, and the placing of these supports exactly in the direction of the cur- rent, are required. An intimate connection between the parts of the roadway, and between the roadway and its supports, is also a great assistance in resisting the current; sufficient play, however, must be left to allow the bridge to accommodate itself to the action of a heavy load in passing over it, and to the action of the waves when the water is rough ; otherwise, however firm the fastenings may be, they will soon work loose. The interval between the supports is regulated not only by the strength of the balks, but also by the cross-section and the buoyant power of the supports. The duties of an officer charged with the construction of a bridge are, to discover and collect all the material disposable for the purpose; to examine carefully the position chosen for the bridge; and to ascertain the width and velocity of the stream, and the nature of its bottom and banks. He can then determine the comi)osition of the bridge, taking care to re- 24 PASSAGE OP RIVERS. serve suiBcient material to repair damages, and to lengthen the structure in case of a rise in the water. He will then divide his force into detachments, assign to each its duty, and require each to lahor at its own task without attempting to interrupt or assist that of any other. During the progress of the work, he will not allow any unnecessary person to approach the working parties, or to step upon the bridge. OHAPTEE II. THE BRIDGE EQUIPAGE. The United States bridge equipage is composed of reserve and of advance guard trains. The former are intended to accompany large bodies of troops in the field, and are provided with the material necessary for the construction of bridges of suflflcient capacity to pass large armies with their heaviest trains over rivers of any size and rapidity. The advance-guard equipage is intended for the use of light troops, such as advance guards, cavalry expeditions, etc. It is organized, both as regards material and carriages, with a view to rapidity of movement. At the same time, it is capable of furnishing a bridge which will fulfil all the requirements of troops engaged on such service. EESEBYB EQUIPAGE. Organization. — This equipage is divided into trains, each of which is composed of four ponton divisions and one supply division. Each division is accompanied by a tool wagon and traveling foi'ge. Each ponton division is comjjlete in itself, containing all the material necessary for constructing a bridge of eleven bays, or 225 feet in length. Each of these divisions is subdivided into four sections, two of which are ponton and two abutment sections; the former contain three ponton wagons and one chess wagon; the latter, one ponton, one chess, and one trestle wagon each. The ponton section contains the material for three baj's, and should never be subdivided. The division may be increased or diminished at pleasure by changing the number of its, ponton sections. The carriages are loaded as follows: Each ponton wagon (Plate III) contains 1 ponton, 7 long balks, 1 anchor, 1 cable, 5 oars, 2 boat-hooks, 20 lashings, 6 rack-sticks, 1 scoop shovel, 2 small scoops, 1 axe, 1 hatchet, 1 bucket, and 20 pounds of spun yarn. Each trestle wagon (identical with ponton wagon, see Plate VI) contains 7 long balks, 7 trestle balks, 1 trestle complete, 2 abutment sills, 2 coils of 3-inch rope. 25 20 THE BRIDGE EQUIPAGE. Bach chess wagon (Plate VI) contains 60 chess. The forge is identical with forge A, furnished by the Ordnance Department. Each tool wagon (Plate X) contains — 50 axes, 20 shovels, 20 spades, 15 pic1(s, 25 hatchfits, 4 broad-axes, 4 adzes, 4 cross-cut saws, 4 hand saws, 12 augers (assorted), 2 orow-hars, 2 caulking irons, 12 tin lanterns. 2 monkey wrenches, 1 sledge, 1 steel square, 1 grindstone, 1 spirit-level, 1 coil telegraph wire, 1 coil 3-inch rope, 1 coil 1-ineh rope, 1 coil spun yarn, 50 lbs. iron (assorted), 25 lbs. paint, 6 paint brushes. 1 lb. red chalk, 4 lbs. white chalk, 6 sail -needles, 1 palm, 6 balls twine, 50 lbs. 6-inch spikes, 100 lbs. 6, 8, 10, and 20- penny nails, 2 sets block and falls, 2 gross each of 1, 2, and 5-inch screws, 1 roll canvas, 20 lbs. caulking cotton. 1 dozen chalk lines. Also four boxes of carpenters' and saddlers' tools nearly identical with those furnished by the Ordnance Department for battery-wagon C. If de- sirable, extra stores to the amount of 500 pounds may be added to the load. The supply division is provided with articles necessary to replace material lost or worn out, such as balk, chess, spare parts of carriages, a few complete carriages, etc. The carriages of this division consist of ponton, chess, and tool wagons, and of forges. Their number and proportion will be determined by the nature of the country in which the army is operating, and by the proximity of the main depot. The ponton wagon contains 17 long and 7 trestle balks. The chess wagon, 60 chess. Tool wagon No. 1 carries the same load as that attached to a ponton division. Tool wagon No. 2 contains 80 rack collars; of 6, 8, 10, and 20 penny nails, 2 kegs each; of 4 and 6 inch spikes, 2 kegs each; of 1, 2, and 5 inch screws, 4 gross each; of 1 and 3 inch rope, 2 coils each. The loads may be increased to the extent that circumstances will permit, by adding spare parts of carriages. The forges are of the patterns A and B issued by the Ordnance Department. Bridge material. — The trestle (Plate I, Fig. 1) is composed of a cap, (Fig.3,) two legs, (Fig.2,) two false legs, (Fig.7,) two shoes, (Fig. 8,) and two suspension chains. The cap is formed of two white-pine planks, 20 feet by 12 inches by 2 inches. These are connected by six blocks, of which four (o o) are of oak; the others are of pine. Between the latter a curved strip of pine (c c) is introduced. The legs are of white pine, 15 feet by 7 inches by 3^ inches, fitted at top to receive the rings of the MATERIAL OF RESERVE TRAIN. 27 suspension chains, and at bottom to enter the mortise in the shoe. The shoe, which is intended to prevent the leg from sinking too deeply into the ground, is also of white pine. It is provided with a key to secure it to the leg. The suspension chains are eight feet long. They are provided with rings at one end to put over the tops of the legs, and toggles at the other for the purpose of securing them to the rings in the cap. The vacant spaces left in the mortises of the trestle cap when the legs are inserted, are filled with the false legs. The abutment sill (Plate I, Pig. 6) is of white pine, 14 feet by 8 inches by 6 inches, scored to mark the position of the balks. For facility of transportation, it is provided with a ring in each end. The ponton (Plate II, Fig. 1) is about 31 feet in length, with a maximum breadth of 5 feet 8 inches. It is of about nine and a half tons burden, and has sufficient capacity to transport forty men, fully armed and equipped, besides its crew of i)ontoniers. In the bridge, it has sufficient strength to sustain the heaviest trains that accompany an army. The details of its construction are given in the following specifications: The floor and side timbers to be of white oak. There are twelve timbers in all — eight, 2 by 3 inches; two, 3 by 3 inches ; two, 4 by 4 inches; and all should be full measurement. The forward and aft side timbers to be finished with mooring posts 10 inches above plank-sheer, 4 inches square at top, and 4 inches in diameter at plank-sheer. The battens (strips between the bottom timbers) to be of pine, IJ inches thick by 4 inches wide. The bow and stern pieces to be of solid oak, 4 inches thick, bevelled for bottom i)lank to fit. The timber plates to be fastened to the timbers by three iron rivets passing through, and well riveted — say, one rivet at each end and one at the turn of the knee. In addition to the rivets, every iron to be fastened by eight No. 18 IJ-inch gimlet-pointed iron screws — say, four in the side timbers and four in the floor timbers. The cavil (piece thi'ough which the hooks for fastening the balks pass) to be of oak, 1 inch thick by 4 inches wide, and to be shouldered into the side timbers ^ of an inch. The boat to have 7 bottom planks, 1 inch thick, running'the whole length of bottom without a joint, and fastened at each timber with two iron rivet-head nails, -^g inch thick by4J inches long, driven through and clinched; and also fastened to each batten by 3-inch clinch nails driven through and clinched. 28 THE BRIDGE EQUIPAGE. Chafing battens to be of white oak, 1 inch thick by 5 inches wide, and to be fastened with 3inch clinch nails driven through and clinched on the inside, except at the ends, which shall be fastened by No. 18 If-inch gimlet-pointed screws, say two at each end. The eight side planks to be each J of an inch thick, and to be fastened like the bottom planks ; and every plank to run the whole length of the boat, and not to be pieced. The lower side plank to be nailed to the bottom (besides the clinch nails) with 10-peiiny cut nails, not over 5 inches apart. Also the chafing battens to be nailed in same way (in addition to the clinch nails) to the lower side plank. The clamp (strip that runs along the top of the timbers ou the inside) to be of pine, 1 inch thick by 3 inches wide, and shoul- dered into the rib flush. The plank-sheer (piece that forms the top of the gunwale) to be of oak or ash, 1 inch thick by 5 inches wide — or wide enough to cover the gunwale; to be nailed to upper side plank and to the clamp with 10-penny nails not over 5 inches apart. Cross-braces to be of spruce, 2 inches thick by 9 inches wide, shouldered on to the timbers | of an inch, and fastened at each end with three No. 18 If -inch gimlet-pointed screws. A blocking not less than 2 inches in thickness, to be put under each row-lock plate, the socket of which should beclosely fitted in passing through it. Locker in the stern to come to the first batten, where a strong bulkhead is to be made; the top plank to be well supporterl, so as to bear the weight of a man. Trapdoor on top to be 2 feet by li feet, with strap hinges put on with clinch nails; door to have hasp and padlock; padlock to have brass tumblers and brass keys. Bach boat to have 14 row-locks ; row-lock plates to be let in flush with top of gunwale. Bow and stern irons (shown iu drawing) to pass entirely round the bottom planking, and to connect on top — all iu one piece, fastened by screws. The boats to caulked in the best manner throughout with cotton, and to be painted lead color, two coats of white lead and raw linseed oil of the best quality being used. The iron work to be covered with black asphaltum varnish. Nail holes to be puttied. The boats are to be neatly and smoothly finished in boat style, no cracks or flaws being filled with putty, and especial care being taken to make tight joints and to avoid splitting timbers MATERIAL OP RBSEEVE TRAIN. 29 or planks. Best quality of seasoned wood and best quality of iron to be used. When furnished by contract, the boats must be carefully inspected on the above specifications, and on all points involving good workmanship or materials. The balks are of two kinds: the long balk, (Plate II, Fig. 4), which isofwhitepine27 feet by 5 inches by 5 inches, is furnished at each end with a cleat or claw of oak, the grain of which crosses that of the balk; the distance between the claws is 25 feet 8 inches. The trestle balk (Plate I, Fig. 4) is also of white pine 21 feet 8 inches by 5 inches by 5 inches; it is provided with two cleats of oak at each end. The claws thus formed have 8 inches of opening, the distance from centre to centre of claws being 20 feet. The ohess (Plate I, Fig. 5) is a white-pine plank 13 feet by 12 inches by IJ inches; the width at each end for a distance of 2 feet, is reduced to lOJ inches, thus forming a notch on each side for the passage of the side-rail lashing. The chess is se- cured from splitting by a rivet, ^^ of an inch in diameter, passed through each end. The middle line across the chess is marked on both sides with a fine saw cut; this is important. Both balks and chess should be made of the best white-pine lumber free from knots, sap, or shakes, and perfectly straight- grained. The saddle transom (Plate II, Fig. 2) is of white pine, 5 feet 4 inches by 8 inches by 4 inches, with a strong iron hook at each end to put over the gunwales of the ponton. There are two small cleats on the middle of the transom, forming a recess to receive the sill. The saddle sill is of white pine, 14 feet by 8 inches by 5f inches. The oars are of the ordinary form, 18 feet in length. The boat hoolc is of the ordinary form, 10 feet in length. The scoop-shovel is of steel, and of the form usually employed for shoveling grain. The small scoop is the ordinary tin scoop used by grocers. The bucket is of India-rubber, of the ordinary pattern. The raclc-sticic is of hickory, 2 feet long and IJ inches in diameter, with a cord 4 feet long passed through one end. The rack-collar (Plate II, Fig. 5j is of strap iron IJ by f inches, made in two parts united by a link on each side. The inside measurement of the collar is 1 foot 7 inches by 5 inches. Pickets are of oak or hickory, 3 feet long by 3 inches in diam- eter, protected at both ends with iron. 30 THE BBIDGE EQUIPAGE. The anchor is the kedge, weighing 150 pounds. The cable is of 3-inoh Manilla rope, 40 fathoms in length. The lashings for both balks and side rails are of 1-inch Manilla rope, 18 feet in length, with a loop at one end. The tar hucTcet is of the pattern issued by the Ordnance De- partment. Carriages and their loads. — The carriages are of four de- scriptions: The ponton wagon (Plate III) differs from the chess wagon (Plate VI) only in being of heavier construction, in having longer side rails, and in the form of the stakes for securing the load. All important details are given on Plates IV and V. The tool wagon (Plate X) differs from that ordi- narily used in the Quartermaster Department only in the form of the body. The forge is identical with that furnished by the Ordnance Department. As mules are usually employed for the transportation of these trains, the ordinary mule harness of the Quartermaster Department is employed, but with this alteration: the traces are continuous, as in the artillery service. When horses are employed, the light artillery harness, with a slight change in the pole straps, will answer. The ponton wagon (Plate III) is loaded by first placing 7 long balks between the side rails, and entering the dowels on the front bolster into the holes made in the balks for this purpose. Above this course of balks is placed the ponton, stern fore- most — the stern rings about 15 inches in advance of the front axle. The ponton is secured by lashing its rings firmly to those of the carriage. The anchor is slung under the side rails; the cable coiled as far forward as possible in the ponton; the oars and boat hooks laid in the ponton, and the small arti- cles stowed in the ponton locker. An axe is placed in the slings on the rear axle. The chess wagon (Plates VI and VII) is loaded by placing a course of 30 chess on edge, with their lower notches resting on the middle and rear bolsters. The transoms are laid on the upper notches abutting against the stakes. A second course of 30 chess is then placed directly over the first. The binders are then hooked on and secured. The ponton wagon is used for the transportation of the trestle and abutments. (Plate VI.) A course of 7 long balks is first placed as described above. The next course consists of 7 short balks and 2 abutment sills. The third, of a trestle cap MATERIAL OF RESEEYE TRAIN. 31 with the false legs thr.ust into the cavities in its top, and the legs lashed against it so as to prevent the false legs from fall- ing out. The suspension chains pass through the rings on the cap, and are lashed to the rings of the carriage. The shoes are strung on the suspension chains; 2 coils of 3inch rope are laid on this load, and lashed to the forward rings of the carriage. The tool wagon (Plate X) is loaded by hanging the crosscut saws on the middle partition, teeth up; placing the four boxes of carpenters' tools in the left rear compartment, with the hand- saws between them and the sides of the wagon; placing the picks in the left middle coinpartment,.with the hatchets on top; placing the pick handles, axes, and some of the short shovels in the left front compartment, and placing the long shovels, etc., in the right compartment. Tabular summary of the reserve train. Remarks. Poutou carriages . Chess carriages . Tool wagon . Porge . Pontons. Balk, loug.. Ealk, trestle . Chess . Trestles, complete . Abutment sills . Saddle transoms . Saddle sills . Anchors - Oars . Boat-hooks - Scoop-shovels. Scoops, small . Pickets . Rack-sticks. Buckets, India-rubber. Axes. Hatchets. Cables . Lashings. Three-inch rope coils, 120 fath- oms each. Tar buckets . Totals Each ponton carriq,ge is drawn by 8 mules or 6 horses; each tool wagon and forge, by 6 mules or 4 horses. Tlie load of the ponton wagon is 2,9Q0pounds; of the tres- tle wagon, 2,635 pounds; of the chess wagon, 2,280 pounds; of the tool wag- on, 2,100 pounds; and of the forge, 1,166 pounds. 70, 888 32 THE BRIDGE EQUIPAGE. ADVANCE-GUARD EQUIPAGE. Organization. — The traias of this equipage are composed of 4 ponton divisions, each of which consists of 8 ponton, 2 chess, and 2 trestle wagons. The load of the ponton wagon (Plate IX) consists of 7 balks, 16 chess, 2 side frames, 1 cable, 1 anchor, and a ponton chest containing 1 ponton cover, 14 transoms, 5 paddles, 2 scoops, 2 mallets, 20 lashings, 2 boat-hooks, 1 scoop-shovel, and 8 rack, sticks. The chess wagon contains 50 chess and 2 spare ponton covers. The trestle wagon (Plate IX) carries 14 balks, 1 trestle com- plete, 1 abutment sill, and 1 coil of 3-inch and I of 1 inch rope. The forge is forge A of the Ordnance Department. "When necessary, this load may be reduced by transferring a part of the tools and coal to a forage wagon. The ponton wagon carries all the material necessary for con- structing a complete bay. The division may, therefore, be in- creased or diminished by one or more ponton wagons without disorganizing it. When a forced march is to be made, and it is desirable to lighten the loads, the chess may be removed from the ponton wagons, the rope from the trestle wagons, and the load of the chess wagons be reduced to 40 chess. The number of the latter wagons in this case mast be increased to 5. The tool wagon is loaded with — 30 axes, 1 monkey-wrench, 2 sets blocks and falls, 40 shovels, 1 sledge, 5 rolls canvas, 4 spades, 1 grindstone, 6 palms, 15 picks, 1 coil wire, 2 doz. sail needles, 20 hatchets, 1 coil 3-inch rope, 1 coil spun yarn, 4 broad-axes, 1 coil 1-inch rope, 12 balls twine, 4 adzes, 30 lbs. iron, assorted, 1 gross 1, 2, and 5 inch 2 crow-bars. Chalk and chalk-lines, screws, 10 augers, Spikes, 6 and 4-inch, 25 4 boxes of tools, similar 2 cross-cut saws, lbs. each, to those of the reserve 4 handsaws, 100 lbs. 6, 8, 10, and 20 train. 10 tin lanterns, penny nails. If necessary, part of this load may be transferred to a forage wagon. Bridge material. — The wood work, with the exception of the claws of the balks and the blocks in the trestle caps, is entirely of white pine. The ponton frame (Plate VIII, Pig. 1) is composed of two side frames, of twelve narrow and of two wide transoms. The former are strengthened at the ends by iron straps, which are ADTANOE-GUABD MATERIAL. 33 countersuDk and perfectly smooth ; all the edges of the frame and transoms are well rounded to prevent chafing the canvas. The wide transoms are of 10-inch by 1^ inch plank, provided with tenons to fit the mortises in the frame. The narrow tran- soms are of 4- inch by 2 J-incli scantling. The articles of each of the above classes should be made exactly alike, so that they may be interchanged. Two of the narrow transoms are provided with an iron mooring becket. The frame when assembled is held together by a rope passed through the rings in the ends of the side frame, and tightened with a rack-stick, (Plate VIII, Fig. 2.) The canvas ponton frame used during the latter part of the war by the army of the Cumberland, was made somewhat dif- ferently from the one which has just been described. The side frames were divided at the middle, the two parts being con- nected together by stout hinges placed on the inside. The upper hinge was attached by screws ; the lower was riveted. A greater number of iiooring pieces were used for the bottom of the boat, and a couple of ropes were run through them , the slack of which was used to tie them into bundles when the boats were disniau- tled. There were also some differences in the framing of tlie sides, and in the kind of transoms used to connect all the parts together. Plate XVI, Fig. 6, shows the hinged canvas ponton frame as modified by the experience derived from the use of the boats first built. The object in adopting this form was to dispense with the necessity of special ponton wagons and trains. All the parts of the bridge, except the balks, could be carried without diffi- culty in the ordinary army wagon. Special wagons were required for the latter, but they were very quickly made by throwing off the body of an army wagon and lengthening the coupling. Under circumstances where it is essential to econo- mize transportation by keeping all teams fully employed at all times, or where a bridge equipage is suddenly prepared and there is no time to procure the regular ponton wagons, the system just described may be used with advantage. Addi- tional wagons can at any time be procured, or broken ones replaced, from the sur^jlus or depot transportation. Single hinged boats for service on the prairies, can be carried without difficulty in the ordinary trains. The only ponton train carried by the army of the Cumber- land from Chattanooga to Atlanta, and thence to Savannah 21638- 3 34 THE BRIDGE EQUIPAGE. and Washington, was composed of hinged canvas pontons, and it gave general satisfaction. The ponton cover (Plate VIII, Fig. 3) is of 0000 cotton duck, double seamed, with the border double for 1^ inches in width. The clew-line eyelets are of metal. The sJiort hallcs (Plate VIII, Fig. 5) are 22 feet by 4J inches by 4J inches, with 20 feet 10 inches space between the cleats, which are similar in construction to those of the reserve train. The chess (Plate VIII, Fig. 4) are 11 feet by 13 inches by IJ inches, with notches 18 incjhes in length; in other respects sim- ilar to those of the reserve train. Tlie anchor is a kedge weighing 75 pounds. T\\% paddle Is of the ordinary form, 8 feet long. The hoat-hooh is of the nsual construction, except that the points are blunted to prevent injuring the canvas; it is 8 feet long. The ponton box (Plate IX) is 8 feet long, 2 feet 4 inches wide, and 18 inches deep; the lid is covered with canvas, which overlaps 3 inches all around. It has strong rope handles at each end. The cable is of 3-inoh Manilla rope, 30 fathoms long. The lashings are of 1-inch rope, 18 feet in length, and looped at one end. The mallet is the ordinary carpenter's mallet. The scoop-shovels are of galvanized iron. The trestles, trestle ballcs, abutment sills, scoop-shovels, scoops, raclc sticks, picTcets, buckets, and tar buckets are the same as for the reserve train. Carriages and their loads. — The ponton wagon (Plate IX) is identical with the chess wagon of the reserve train (Plate VI). It carries all the bridge material of the advance-guard train. The loads are arranged as follows : To load with the canvas ponton, (Plate IX), 7 common balks are laid between the rails and on the right side, where they are secured by the front bolster dowels ; on the left, 8 chess are placed on edge, with their notches resting on the middle and rear bolsters. The two side frames are laid over the balks, with their bottoms against the chess. The wagon transoms are laid in the upper notches, of the chess, and abutting against the stakes. Eight more chess are laid directly over the first course. The ponton chess, containing the canvas cover, transoms, lash- ings, rack-sticks, scoops, scoop- shovel, paddles, boat-hooks, and mallets, is placed on top of the side frames and.against the chess. The binders are hooked down ; the side frames are lashed ADVANCE-GUARD MATERIAL. 35 by their rings, and the chest by its handles, to the rings of the wagon. The cable is coiled on the side frames and in front of the chest, where it is lashed. The anchor is slang "under the side rails, and an axe on the rear axle. The wagon, loaded with the trestle, (Plate IX,) has 7 short balks and 2 trestle balks in the first course; 5 trestle balks, 1 sill, and 1 trestle-cap in the second; and 1 coil of rope and 2 trestle-legs in the third course. The legs are lashed on top of the trestle; the small parts are packed as in the reserve train. The wagon is loaded with chess by first placing a course of 30 chess as in the reserve train, (see Plate VI,) and on these a second course of 20 chess, 10 of which are lashed against the right and 10 against the left wagon stakes. The lashings pass through the wagon rings. A light box containing 2 spare can- vas i)ontou covers is lashed in front of the chess, and resting on the front bolster. The tool wagon is loaded as in the reserve train. Tabular summary of the Advance-guard Train. Articles. law tao-s Ponton carriages Tool wagon Forge Pontons, complete Trestles, complete Abutment sills Balks, short , 'Balks, trestle - - . Chess Anchors Paddles , Boat-hooks Scoop-shovels - Scoops, small Pickets Rack-sticks Buckets, India-rubber Axes, (on rear axles of wagons) . Mallets Ponton chest Cables Lashings ('oils of 3-inch rope Tar bucket Totals . 12 1 1 8 2 2 70 14 228 8 40 16 8 10 8 64 8 8 16 8 8 160 4 14 Lbs. 1, 760. 1, 700. 2,217.0 510.0 472.0 130.0 90. 90.0 33.0 75.0 4.0 3.5 5.0 2.0 7.0 0.8 3.0 5.6 3.0 150.0 45.0 0.5 180.0 7.0 Lbs. 21, 000 1,700 2,217 4,080 944 260 6,300 1,260 7,524 000 160 50 40 32 56 51 24 44 48 1,200 300 80 720 98 48, 854 Kacli of these carriages is - fi.K.Ur«cn det. LOADINOr I'Hl-: PONTOX CAKRIAGJ^ Bv M^ftns of C«skR. ■X ffi M fig. 4. By the SidP 5 C Fig.j Fig. 7 TresU- rEMPORABY TRESTLE BBIDOE Pus 6 RiKl Elevolioa TIWBKK RAFTS Fig. 9. HAFT OF CASKS. I ? Bjimjaifiip^? Fig. K. ^ i"Ui4 »nd 16 D.S. BRIDGE EQUIPAGF. rinU- XVI PILE BRIDGES. Sectiou . a3E3SSEP ^■ ^apyuyagsp^spWi*'*^^ I """M J s ► r*- J il FitiG. Ilii\^r.d Poiiton . O o Hi live aiu wWA. riveta . isr 1 ScatcR^'toraiidt^to V. Upper Midtlle Trausoin B-H-Oreen ilrl . TJ.S.BRIItjirSTRUCTION OF BRIDGES. jili rrrr^T^ B>R>Orocn del