U.S. Marine Corps - Small Wars Manual (1940 Edition)

Chapter VI. Infantry Patrols

Section XI
RIVER CROSSINGS

								Par.
Introduction							6-88
Availability of means						6-89
Swimming							6-90
Bridges								6-91
Boats								6-92
Ferries								6-93
Fords								6-94
Rafts								6-95
Crossing unfordable streams with usual infantry equipement	6-96
Crossing horses and mules					6-97

6-88. Introduction.-a. The passage of a patrol across a stream in small wars operations is similar to the passage of a, defile. It should be assumed that every crossing will be opposed by the enemy, and necessary precautions should be taken to effect the passage with a reasonable degree of safety. The security measures taken and the tactics employed to force acrossing against opposition in small wars do not differ from those of major warfare.

b. All streams act as obstacles to a greater or lesser extent. Some means must be devised to get the troops and material across without disorganization and in condition effectively to resist an enemy attack before, during, and after crossing. Crossing may be. opposed or unopposed. The probability of opposition is frequently the determining factor in the choice of a crossing site. Poorly adapted sites may have to be used by the reconnoitering parties. Time is a factor in every crossing and the means employed must be those that will permit a crossing in the minimum of time to avoid continued separation of the parts of the patrol by the river.

6-89. Availability of means.- Means of crossing may be divided into fords, boats (including rubber boats of the collapsible variety), rafts, ferries, permanent and temporary bridges, and swimming. It may be necessary to make use of several or all of these expedients for the crossing of a body of troops with its supplies. It may be said that fording and swimming will be the normal means of crossing in small wars operations.

6-90. Swimming Most unfordable streams, especially in small wars operations, will have to be crosses, initially at least, by swimming, until protection for the main crossing has been establishe on the opposite bank. Most men will be incapable of swimming even a short distance with their rifles, belts, and clothing and would be helpless and naked when they landed on the opposite bank it they discarede this equipment. Swimming is therefore usually combined with some such method as the use of individual floats or rafts, or the use of the few boats available for the transport of arms and supplies. Such floats may assist the swimmers in keeping afloat while crossing relatively wild rivers. When the men land, they establish themselves in a position that will protect the crossing, assist on the far side in construction of bridges, ferries and similar means of getting the remaining troops and supplies across, or proceed on their assigned mission, which may be to drive an enemy detachment form a more suitable crossing place. Life lines may be stretched across the river one above and one below the crossing, as safety measures to prevent men from being swept away downstreatm by the current.

6-91 Bridges-a.- The construction of bridges for the passage of arms requires considerable time and material, and a certain amount Of technical engineering training. Bridges are most useful at crossings on the line of communications and have the advantage of providing a permanent means of crossing a river. Only those forms of bridges easily constructed with materials or tools available at the bridge site will be considered here.

b. Felled tree- Very narrow streams may be bridged by felling a large tree across the stream, staking down or otherwise securing the ends, and then cutting off the branches above the water so that troops can walk across. A line can be stretrhed as a handrail if necessary from bank to bank over the fallen tree trunk.

c. Foot bridge of two or more trees.- Where one tree will not reach across the stream, two trees may be felled on opposite sides of the stream, and their branchees and tops secured together in midstream. Lines should be made fast near their tops before felling, and the line snubbed to other trees well upstream and eased downstream by the ropes until the two trees intertwine. Then the tops should be securely lashed together and the branches cleared to provide a footpath over the tree trunks. Stakes on either side of the felled tree trunks may he used to strengthen this bridge, A third tree, felled so that its top falls on the point where the other two meet in midstream, but at an angle to them, will strengthen the bridge, as it provides a tension member against the force of the current.

d. Floating Bridges- Floating bridges may be constructed of rafts or boats, with planks laid across the gunwales. These boats should be securely anchored or moored with their bows upstream. Sections of the bridge may be constructed and floated downstream into place. It is desirable to have all the floats of about the same capacity, to avoid extra strain on the planks or other flooring. The larger boats or rafts may be placed at greater intervals than the smaller, to accomplish the same purpose. Rafts or floats may be made of timber, casks, barrels or anything at hand that will float.

6-92.Boats.-a. In the countries in which small wars opertrations usually occur, some native boats will be found in the vicinity of river crossings which are too deep to be fordable. These will normally be of the dug-out type which are quite unstable, but unsinkable. Their capncity will range from small, tow-man boats, to bateaux of 30- or 40-man capacity. If the crossing is opposed, it is desirable to have a sufficient number of boats available to execute the crossing of the patrol promptly. If the passage is unopposed, even one small boat will be found of inestimable value.

b. If no boats can be found in the locality, it is sometimes necessary to construct makeshift boats from available materials. In recent small wars operations, boards found in a local dwelling were used to construct a 6- by 22-foot boat, caulked with gauze from the, hospital corpsman's kit. It was employed to ferry a patrol of 13; officers and men and 70 animals across a stream swollen with torrential rains which made the customary fording impossible. The current was so swift that the use of a raft was impracticable.

c. Collapsible rubber boats, which can be carried by patrols in the field or dropped by aircraft in case of necessity, will probably be used extensively in future small wars operations.

6-93.Ferries.-a. Ferries may be either "flying" ferries or "trail" ferries, and in most streams the current can be used to propel them. If the current is too sluggish, a "rope" ferry may be used; i.e. the boat or raft is drawn across the stream by pulling on the rope or by poling. "Trail" and "flying" ferries are propelled by the current by holding the boat or float at an angle to the current, either by means of ropes or by rudders, or even by paddles held in the water. The angle and the speed of the current controls tbe speed of the ferry and since the angle may be varied the speed can also be controlled.

b. Trail ferry.- A good trail ferry may be constructed in most streams that are not too wide by stretching a ropo or cable (several telegraph wires twisted together will do for a small boat) across the stream and rigging a pulley so that it will travel on this line ("sheer line"). A line is then fastened to the pulley from the bow of the boat. Some ferries, especially in slow streams, must be controlled by a bow and a stern line ("maneuvering ropes") attached to the pulley. By hauling in on the bow line and slackening the stern line, or vice versa, the bow may be set at such an angle to the current that the force of the current, acting on the hull will cause the boat to move across the stream. In a swifter current, where the boat points more nearly upstream, a paddle may be held over the downstream side at the stern, or a rudder may be used.

c. Flying ferry.- A flying ferry uses the same means of propulsion, but in place of the "sheer line," there is an anchorage upstream to which a long line is fastened from the bow of the boat, enabling the boat to swing like a pendulum across the stream. The line is supported by floats at intervals, so that it will not trail in the water and slow up or even stop the ferry. In narrow streams it may be possible to find a curve in the stream that will permit the anchorage to be on land, but still above the center of the stream at the point where the ferry crosses. An island is also a convenient location for an anchorage. The cable mnst be long enough so that the ferry will not have difficulty in reaching both banks.

d. Rafts as ferries.- Rafts may be used in all types of ferries, but they should be so constructed that the current will act against thme efficiently, and so that they may be easily maneuvered but hard to swamp.

6-94 Fords.-a.The requisites of a good ford are low banks, no abrupt changes in depth of water, the bottom offering a firm footing for men and animals and the current moderate. One of the first duties of the reconnaissance parties of a patrol or larger detachment on arriving at a stream is to reconnoiter for fords and bridges in the vicinity, and when found, to test them and define their limits. Dangerous fords should be marked before use by the main body. Fords that show signs of use are likely to be passable, but care must be taken to allow for the height of the water above normal. This may be ascertained by an examination of the banks, especially of the vegetation on the banks and of small trails parallel to the water. When fording swift shallow streams with native pack animals, each animal should be led and not herded across. When the water is deep enough to reach the pack, the cinch may be loosened and two men accompany each animal, one on either side to raise the sugar, coffee, and similar loads to their shoulders in the deep water. Rain in the uplands, which are drained by rivers, may cause sudden floods. These floods rapidly descend the rivers, and make it dangerous to use fords until after the swollen streams subside.

b. Fords may be improved in very swift streams or during freshets by felling trees across the stream and lashing their ends together (narrow streams only) or by fastening a line of floating obstacles such as logs or barrels above, the ford, to cut down the current, at least on the surface. A life line should be stretched across the stream for the crossing of large numbers of troops, and men should hold on to this line. Crossings should be guarded by good swimmers and by boats downstream if available, to take care of those who may be swept off their feet or who may strtay from the ford. Infantry may ford a stream in a column of squads, by men in each rank holding on to each other abreast. The distance between ranks is greatly lengthened to avoid the increased resistance which might be caused by partially damming the stream. Mounted men pass over the ford in column of twos or files.

6-95 Rafts.Rafts may be constructed of any materials that will furnish sufficient buoyance, and which are available at or very near the point of crossing. Many woods do not have enough buoyance even when dry, and this is especially true of green hard woods. "GI" cans with burlap or other cloth under the covers, to make them watertight casks and barrels, gasoline drums and other containers may be used to give buoyancy to a raft. In general the construction of rafts to effect a crossing will be inadvisable except for the heavy articles that cannot be conveniently crossed by other means. Rafts drift more than boats, and must therefore be started across farther upstrearn than boats. Rafts may be used for carrying equipment of men who cross by swimming or for the assistance of those who do not, swim well enough. These individual rafts may be made of two logs with a board or two across them, reeds bound together (or bound banana stacks), or inflated rubber bags. Large rubber bags have been carried by patrols operating on or near the rivers. These bags were made from coffee sacks by coating the sacks with crude rubber. They were larger than sebags, andwould hold one man's personal belongings and equipment. When partially filled with aiir adnt the mouth tied securely, they floated indefinitely, with sufficient buoyancy to support a man in the water.

6-96. Crossing unfordable streams with usual infantry equipment.- a. Recent experiments by the Philippine Scouts have resulted in a method of stream crossing making use of little else besides the equipment usually carried. This method is believed to be superior to most methods of crossing by swimming. It is suitable for crossing in the face of opposition, its rapidly gives it great tactical value, and should cut down casualties considerably.

b.The two-man rifle float.-This float can be prepared by two men in 7 minutes. The two shelter halves (one on top of the other) are placed on the ground, and the remainder of the two packs and the clothing of the two soldiers are placed in the center of the canvas. Now the rifIes are placed (crossed to give rigidity) on top of the packs and clothing. The float is completed by binding the 4 corners of the outside shelter half to the four extremities of the rifles by means of the shelter tent ropes.

"In a similar manner, using two 3-foot sticks or shelter tent poles instead of rifles, a machine gun complete can be floated in a shelter tent.') ("Infantry Journal" for March and April, 1933.)

c.In the construction of the above float, bayonets are attached to rifles, with the scabbards on, to give greater length. A very little untying will make the rifle available to the man after landing on the opposite side since slip knots are used. AS no additional materials are required this method is suitable for almost any stream crossing, even for deep fords, and is available to detachments who must go up or down the streadm to make a land attack on forces opposing the use of a ford or ferry. Canvas is more nearly waterproof if wetted before making up the float.

d.Use of poncho in two-man float with horseshoe rolls.

(1)A method of constructing a two-man float using ponchos and the equipment usually carried in small wars operations was developed at the Marine Corps Schools along the lines stated in subparagraph b. above, and has met tests satisfactorily. The float is made up of the rifles, ponchos, and shelter tent guy ropes. It contains: the horseshoe rolls consisting of one blanket, spare shit of underwear, toilet articles, food, the cart ridge belts, canteens, haversacks, and bayonets of two men, as well as their clothing and shoes which they remove. The horseshoe roll has the poncho on the outside of the blanket with the shelter tent guy rope used for lashing.
(2) To make the float.- (a) Remove the poncho and shelter tent guy ropes from the horseshoe roll. Fold the poncho the long way with the head hole at the side, and lay it flat on the ground. (b) Lay the two cartridge belts on top of the center of the poncho, ammunition pockets down, so that one bayonet and one canteen wil be on each side. (c) Lay the horseshoe rolls on top of one another on th cartridge belts with their long dimensions parallel to the longest side of the folded poncho. Buckle the two cartridge belts around both rolls and slip the end of each bayonet under the other cartridge belt to hold the sides of the bundle rigid. See Diagram No. 1. (d) Take the haversacks and place them on edge in the space in the center of the horseshoe rolls. Men remove their shoes and place on pair on each side of the bundle so as to build out the sides. (e) Lay the two rifles, crossed to form an X, on top of the bundle with their ends pointed at the gour corners of the folded poncho. Lash the rifles where they cross, with a waist belt to hold them in place. See Diagram No. 2. (f) Then the two men, starting at opposite ends of the same rifle, fold the corner of the poncho up over the rifle end, and wrap the sides of the poncho corner up around it, lashing the poncho around the rifle end with one end of the shelter tent guy rope. (g) The two men, next pass to the other rifle and wrap its ends in the two remaining corners of the poncho, lashing them in place with the bight of the shelter tent guy rope. The remaining end of the rope is then lashed to the next rifle end so that the float will be held in place by lashing between all four rifle ends. Care should be taken to wrap the corners of the poncho around the rifle ends and lash them so that water will not enter the float readily if one corner dips under. Diagram No. 3. (h) Place the other poncho, folded twice, over the top of the equipment in the float and tuck the sides down around the edges of the equipment.
(3) When making up this float, stow the equipment and lash the rifles, in such a way that the float will be regular in shape, flat on the bottom, and not too high. so that it will float on an even keel and not tend to upset easily. The two men swimming with the float should be on opposite sides of it and use a side stroke to swim, leaving one hand free to guide the float. If desired, the men can take turns pushing the float ahead of them with both hands, the float keeping their heads out of water while they paddle with their legs.
(4) Trained men need about 5 minutes to make these floats, exclusive of the time they spend removing their clothing. Care should be taken in lashing the float to use slip hitches that can be removed quickly when the line is wet, so that the rifles can be used instantly once the river is crossed.
(5) Similar larger floats mny be improvised, by using wall, etc., tent flies with the upright poles or ridge poles.

e. Other canvas floats-All canvas floats should be wide enough to prevent their capsizing easily, and the loads should have sufficient bulk in proportion to their weight so as to give buoyancy to the whole float. A light frame of boards or sticks will help in the case of heavy articles. Patrols and larger detachments may easily carry extra line for use in establishing lifelines for crossing streams, for starting animals into the water, etc., by wrapping about 30 feet of line, one-fourth inch in diameter, about a man's body just below the belt. (Many natives habitually carry such a line on their bodies when contemplating crossing streams. ) Stronger lines may be carried by patrols using pack animals carrying the lines as top loads. These lines serve as picket lines during halts, and may be used in the construction of ferries. Extra canvas may be carried in the form of tent flies, which are used to construct floats and as shelters for galleys or other purposes in camp. The inclusion of these few pounds of extra equipment may actually increase the mobility of a patrol. If strong vines grow near the river, they may be used as ropes in lashing trees together to obstruct the current,in lashing rafts together, as lines for small flying ferries, or as life lines. It is presumed that all patrols will include some machetes in their equipment when operating in the small wars situations.

6-97.Crossing horses and mules.- a. A stream that is too deep to be crossed by fording presents a very serious obstacle to a unit which includes riding or pack animals, and particularly so if the unit be operating in hostile country. Horses and mules can ford with relative ease streams that are difficult if not impossible to ford by men on foot. To cross animals, their cargo loads and equipment over a stream too cleep or too swift to be forded is an operation to be undertaken only when the situation permits of no other course of action. The difficulties of such a crossing increase with:

(1) Width of the stream.
(2) Swiftness of the current.
(3) Size of the command (No. of animals).
(4) Slope of the banks, particularly on far side.
(5) Hostile opposition encountered.

The width and the current are difficulties which are correlated. For any given width of stream, the animal will be carried farther downstream as the current is increased. Since some animals will naturally swim faster than others, they will arrive on the far bank dispersed over a wide front. This front will sometimes be several hundred yards wide. When the animals arrive on the far bank, they must arrive at a point where the bank is not too steep or the footing too poor for them to get out, of the water. Many horses will be drowned if a good landing place of suitable slope, width, and footing is not available on the far bank. Unfordable streams have been and can be crossed by single riders and by very small patrols but even the most daring and boldest leaders have hesitated to cross such streams. Many of the smaller streams rise and fall very rapidly. The unit leader should bear this in mind. Frequently it will be advisable to increase the rate of march so as to arrive at a crossing before an expected rise, or to decrease the rate so as to take advantage of an expected fall before crossing.

b.When the patrol includes riding or pack animals, these are usually taken across the stream by swimming. Mounted patrols in small wars usually cross by swimming with full equipment. Sometime the saddles and all equipment except the halter and snaffle bridle are removed and ferried across by boat or raft, and the rider removes most of his clothing. Pack animals are unpacked and unsaddled. The rider then mounts and rides the horse into the water at a point well upstream from a good landing place on the other side. The reins should be knotted on the neck, and only used when necessary to turn the horse, and before the horse gets beyond his depth in the water. Horses that are unwilling to take the water may be ridden behind other horses or tied behind boats or rafts. When the horse enters deep water, the rider slides out of the saddle, or off the animal's back, and hangs onto the mane or halter on the downstream side, keeping low in the water and stretching out. Care must be taken to avoid being struck by the horse's front feet, and not to throw the animal off balance by putting too much weight on his head and neck. A swimming animal may be easily guided across a stream and prevented from turning back by the rider resting slightly forward of the withers and pushing the horse's head to the front with either hand if he attempts to turn. If the horse gets too excited, it may be necessary to release the halter or mane, and then catch the horse's tail and hold on. The horse should be kept headed upstream , especially in a swift current.

c. A much quicker and easier method of swimming animals is to herd them across, but animals not trained or practiced in swimming are often difficult to herd into water, and often turn around and come back when halfway across. (Herding should not be attempted in a swift current.) Sometimes the appearance of a few horses or mules on the opposite bank will help to start the herd across, and those which are seen to turn back in midstream may be kept, out of the herd and crossed individually later. Some animals will have to be forced into the water. This may be done by passing a strong line across the rump of the animal and manning each end, a good rider then mounting the animal, and having a long lead line pulled by a man in a boat or on the other side of the stream. In dangorous streams it may be necessary to run a strong line across, ancl have a lead of at least 10 feet long tied to a pulley or sliding ring on the line ancl tied to the horse's halter with two leads of smaller line on the ring from each bank. The horse is then put into the water, head upstream , and drawn over to the other sicle by men pulling on the line and by the horse swimming. The ring is then drawn back for further operations. If the ropes do not fail, no horse can be washed (downstream, and if done promptly, none should be in danger of drowning, as the tendency of this pulley method is to force the horse's head up. Sheer lines for trail ferries may be used in this manner, but it is usually more economical to lead the horse behind the ferry. A few difficult horses may be crossed by simply carrying a line from the horse to the other side of a narrow swift stream, holding it at a point upstream from the landing, and letting the horse swing across the stream and land on the other side (as is described in par. 27-7 e, for Flying Ferries). As this requires more trouble than any of the other methods, it should be used only when there are few such difficult animals, and when other methods fail.

d. Mounted Marines should be thoroughly trained in swimming their mounts and in fording. Practice of this kind makes the animals willing to enter the water, and saves much time in emergencies. With light equipment , mounts may be crossed by swimming with the saddles on. The cantle roll aids bouyancy rather than detracts from it.