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

Chapter X. RIVER OPERATIONS.

SECTION IV
OCCUPATION OF A RIVER

					Par.	
The mission				10-18
Similarity to land operation		10-19
The day's march				10-20
Rate of movement			10-21
Boat formation				10-22
Reconnaissance and security		10-23
lnitialc ontactw itht heenemy		10-24
Atypical ambush				10-25
The attack				10-26
Garrisoning the river			10-27
Defensive meagures			10-28
Passage of obstacles			10-29
Night operations			10-30
Supporting forces			10-31

10-18. The mission.--The missions which determine the necessity for the occupation of a river line have been stuted previously: to provide an easier and more economical route of supply to the land forces; to deny the use of the river to the hostile forces; to interfere with enemy lines of communication which are perpendicular to the river line; or to secure an avenue of approach to the hostile area for the establishment of a base from which active land operations can be conducted. Each of these will affect the size and composition of the force employed, and the location of the garrisons established along the river.

10-19. Similarity to land operations.--The occupation of a river parallels in every respect the advance of a land patrol from its base, except in the means of transportation. After the initial base at the mouth of the river has been seized, a first objective is selected and patrols are pushed forward until it is captured. Reorganization takes place, supplies and reinforcements are brought forward, and the advance is resumed to the second objective. A third objective is selected and taken in the same way, and so on until the river is brought under control. If opposition is not expected and the mission is to garrison the river more or less equitably throughout its length, as in the case of using it as a route of supply or to deny it to the enemy, the advance may be continuous. The entire river force may leave the original base as a body, provided enough boats are available, and detachments are made as each outpost is established along the route. If opposition is anticipated, or if the supply of boats is not sufficient for the entire patrol, the advance will certainly be made by bounds from objective to objective, and eventually the major portion of the river force will be concentrated at the final objective where it is employed for coordinated land and river operations against the enemy in hostile territory.

10­20. The day's march.--As with land patrols, the day's march should begin as soon after dawn as possible. This is facilitated by the fact that most of the supplies and equipment may be loaded into the boats each evening as soon as the rations for the next 24 hours have been removed. Noonday halts should not be made for the purpose of preparing a hot meal. Midday lunches may be prepared ancl distributd in the morning although usually the ration situation will not permit such action. Unless tactical considerations prevent, the day's movement should be halted at least 2 hours before sundown in order to carry out the necessary security measures, make the camp, and feed the troops and boat crews before dark. The camp should be on fairly level ground, sufficiently above the water level to avoid flooding in the event of a rapid rise in the river during the night. Boats should be secured with a sufficiently long line to prevent their being stranded on dry land because of a sudden drop in the water level, or being pulled under and swamped because of a sudden rise in the river. Boat guards should always be posted over the flotilla.

10-21. Rate of movement.--The rate of movement will depend upon the type of boat being used, whether propelled by motor or by hand; the nature and condition of the river, whether in deep comparatively calm water, or in the strong currents and innumerable rapids of the middle and upper river; and the need for careful reconnaissance. A motor flotilla may average between 60 and 100 miles a day under the best conditions; a flotilla moving by hand power will average from 12 to 15 miles per day. The rate of advance will be that of the slowest boat in the column. Regardless of the rate of movement, some word of the approach of the patrol will usually precede it up river, especially if the area is well populated. If the state of the river permits, it may be possible, and in certain situations desirable, to overrun the hostile shore positions by utilizing the speed available to a motorboat flotilla. If the mission of the patrol is to drive the hostile groups out of the river valley, it may be better to advance slowly, sometimes by poling, in order to seek out the enemy by reconnaissance and engage him in combat.

10-22. Boat formations.--a. General.--Formations for a boat column advancing along a river, either up or down stream, parallels in every respect a march formation for an infantry patrol over land, and the same principles apply. (See "The Infantry Patrol," ch. VI). There should be an advance guard, a command group, a main body, a combat or supply train, and a rear guard. Tactical units, such as half squads (combat teams), squads, and platoons, should be assigned to separate boats so as to maintain freedom of maneuver and yet retain as much control over the various elements of the patrol as possible. The number and type of boats within the formation will depend upon the size and composition of the patrol and the nature of the river in which it is operating. Even in the lower river where no opposition is expected, some security elements should proceed and follow the main body. It would be a mistake to place an entire patrol consisting of a rifle platoon in a single lower river boat, or even to divide it into a point of a half squad in an upper river boat and the remainder of the patrol in a single lower river boat, if opposition is anticipated. To do so might immobilize the entire patrol if the main body should suddenly be fired upon from a concealed hostile position. On the other hand, it would be tactically unsound to employ only upper river boats containing one squad each or less for a patrol consisting of a reinforced rifle company. This would result in an elongated column and a corresponding lack of control. If the nature of the river and the type of boats available make such a disposition necessary, it would be better to employ the split column formation, described in Chapter VI, for large infan{ry patrols.

b. Type of boat employed.-­The elements of the advance guard, the rear guard, and flank security units, as well as the command group should be assigned to small, light, fast boats of the upper-river type. This is especially true of the point, rear point, and command group. This facilitates the movement of the security elements and permits them to adjust the distances in the formation according to the terrain through which they are passing without slowing up unduly the steady progress of the main body. Itenables the patrol commander to proceed rapidly to any part of the column where his presence is most urgently required. The remainder of the patrol may be assigned to types of boats which are best suited to the tactical requirements and the nature of the river.

c. Distances in formation.--The distances bewtween the elements of the column will vary with the terrain, the size of the flotilla, and the speed of movement. The principles involved are analogous to land operations in which the troops are proceeding along a fairly wide, open road. The leading elements should never be out of sight of the next element in rear for more than a minute or two at a time. Where the river is straight and wide, distances between the various parts of the column should be great enough to prevent the main body coming under machine-gun fire before the hostile position has been disclosed by the security detachments. Where the river is winding and tortuous the distance between goups should be shortened. If the distance between elements is too great each unit may be defeated in detail before the next succeeding unit can be brought up, disembarked, and engaged with the enemy.

d. Location of patrol commander in column.--The patrol commander's boat will usually move at or near the head of the main body.

e. Location of supply boats.--Normally the supply boat or boats should be located at the tail of the main body. The rear echelon of the command group acts as train guard. In the event of combat, the train guard assembles the boats of the flotilla and the crews, and moves the train forward to maintain liaison with the main body as the attack progresses. If the rear guard is committed to action, the train guard assumes its functions to protect the column from an attack from the rear. If the train is unusually long, as may be the case when a patrol is to establish an advance base at the end of its river movement, it may be advisable to detach the majority of the supply boats from the main column and form it into a convoy, following the combat part of the patrol at a designated distance.

10-23. Reconnaissance and security.­-a. Methods of reconnaissance.--A river patrol employs the same methods of reconnaissance (See "The Infantry Patrol," ch. VI.) as an infantry patrol ashore. Since the route of advance is limited to the river, it is often necessary to halt the movement temporarily while small land patrols reconnoiter suspicious localities some distance from the river banks.

b. The advance guard. The advance guard may consist of a point boat only, or it may be broken into a point, advance party, support, and reserve, depending upon the strength of the patrol. As in operations on land, the function of the point is primarily reconnaissance, to uncover and disclose hostile positions in front of the advancing column before the main body comes within eflective range of the enemy's weapons. The upper-river type boat is best suited for this purpose; it can be handled easily and does not expose too many men to the surprise fire of an ambush laid along the shore lines. The elements of the advance guard should increase in strength from front to rear so that increasing pressure is applied as succeeding units engage the hostile position. If the river is wide, the advance guard should employ a broad front, with at least one boat near each bank. The main body should proceed near the center of the river to reduce the effects of hostile fire from either bank.

c. Flank Security.--(1) It is almost impossible for men in boats to discover a well-laid ambush. When operating in hostile territory, or when there are indications that combat is imminent, shore patrols should precede or move abreast of the advance guard boats on each bank of the river. Although this will slow the rate of travel, it is an essential precaution unless speed is the most important factor in the mission of the patrol.

(2) Navigable tributaries entering the route of advance should be reconnoitered and secured by some small boat element of the patrol while the column is passing them.

d. March outposts.--March outposts should be established at every temporary halt. This is accomplished by reconnaissance to the front and rear by the point and rear point, respectively, and by the establishment of flank boat or shore patrols as necessary.

e. Security at rest. -- Immediately upon arriving at a temporary or permanent camp site, boat reconnaissance patrols are sent up and down river for a distance of one or more miles depending upon the nature of the river. Trails and roads leading into the camp site and suspicious localities in the vicinity of the site are reconnoitered by land patrols. Other precautionary measures are taken as prescribed for infantry patrols. (See "The Infantry Patrol," ch. VI.)

10--24. Initial contact with the enemy.--The initial contact with the enemy in river operations may be in the nature of a meeting engagement, with all the elements of surprise for both forces found in such contacts, or, as is more often the case, it consists of uncovering his outpost positions. In either event, once contact has been made, the choice of position and the time of future engagements will pass to the hostile force attempting to prevent the further advance of the patrol. In most small war operations, these engagements will be in the nature of an ambuscade.

10--25. A typical ambush.--The typical hostile ambush will resemble those found in land operations. It will be located at a bend in the river in order to provide suitable locations for automatic weapons to enfilade the advancing column of boats. The nature of the river will be such that the boats will be forced close to one bank to negotiate the current. Along this bank will be located the main hostile position so sited that rifle and automatic weapon fire can be directed at the column from the flank. The terrain will be heavily wooded to afford cover and concealment. Under these conditions, the possibilities that the ambush can be detected by men in boats will be very slight. Portages, rapids, and canyons may also be selected as ambush positions in order to engage the patrol when it is widely dispersed and out of control of its commander.

10--26. The attack.--Men in boats present a concentrated, vulnerable target to a hostile force ashore. The hostile fire should be returned by the weapons carried on the boats as normal armament. A few riflemen may be in such a position that they can open fire without endangering the crew or other members of the boat. However, any fire delivered from a moving boat will be erratic and comparatively ineffectual. The full power of the attacking force cannot be developed until the troops are on shore and deployed for the fight. If the attack occurs in a wide, deep stretch of river in which the boats can be maneuvered, it may be possible to run past the hostile fire and land the troops above the ambush to take the attack in the rear and cut off the enerny's prearranged line of retreat. Usually the ambush will be so located that this is impossible. In that event, the leading boats should be beached toward the hostile position. Disembarking, the men in these boats take up the fire and hold the hostile force in its position. Those boats not under the initial burst of fire should be brought upstream as close to the hostile position as possible, the troops disembarked, and the attack launched from the flank to envelop the ambush, overrun the position, and intercept the hostile line of withdrawal. Ordinarily the patrol should land on one side of the river only. In some sittlations it may be desirable or necessary to land on both banks, especially if the hostile force is deployed on both sides of the river. This action increases the difhculties of control, and may result in inflicting casualties among friendly personnel. Once the troops are ashore, the tactics are similar to those employed by regular infantry patrols.

10--27. Garrisoning the river.--a. The location of the various posts to be established along the river is determined by: foreign settlements and investments which require protection; junctions of important river-ways; location of intersecting roads and trails; supply dumps and reshipping points between the lower and middle rivers or the middle and upper rivers; and the strength, aggressiveness, and disposition of the hostile forces.

b. The strength, of each post will depend upon its mission and the hostile forces in the area. The largest forces should be located a.t those points on the river which are most vulnerable to attack, or fronl which combat patrols can operate to best advantage against hostile forces.

c. The distance between posts on the river is determined by the existing situation. If the hostile force is active and aggressive in the area, the posts should be within supporting distance, not over 1 day's travel upstream, from each other. If the hostile force is weak, unaggressive, or nonexistent, a distance of 150 miles between posts may not be too great a dispersion of force.

d. In some situations, it may be necessary to establish outposts on navigable tributaries to the main river in order to protect the line of communications. This is especially important if the tributary leads from hostile areas or if trails used by the hostile force cross its course.

10--28. Defensive measures.--a. Each garrison along the river must be prepared for all-around defense. Wire entanglements or other obstacles should be erected, machine guns and other defensive weapons should be supplied, and normal defensive measures taken. Active patrolling by land and water should be maintained. Communications by radio or other means should be established with the area headquarters and with other outposts along the river. Boats should be supplied to each outpost for reconnaissance, liaison, and local supply purposes, and as a means for evacuation down river in case of necessity.

10-29. Passage of obstacles.--Obstacles in the river, such as narrows, gorges, bad rapids, and falls, whether they can be navigated or require a portage, are similar to defiles in ordinary warfare and similar protective measure must be taken. A combat patrol should proceed to the head of the obstacle, and flank security patrols should reconnoiter both banks of the river and dangerous commanding localities, in order to secure the safe passage of the main body through the obstacle.

10-­30. Night operations.--Night operations may be conducted:

• (1) To make n reconnaissance.
• (2) To make a search.
• (3) "To secrete small detachments and picket boats.
• (4) To send out a patrol.
• (5) To change the location of a post.
• (6) To avoid aimed fire from shore and to avoid combat. Night operations must be conducted by poling or paddling, never by motor, if secrecy is to be attained. Movements upstream against the current at night are extremely slow, difficult, and fatiguing to crew and combat force alike. They should be avoided except in the most urgent situations. They have all the attendant difficulties of a night march by an infantry patrol. See "The Infantry Patrol," Ch. VI.) On the other hand, night movements by boat downstream with the current can be silently and easily executed if the night is clear and if the river is free of dangerous obstacles. Such night movements are often profitably employed in river operations.

10-31. Supporting forces.--a. Infantry patrols. River operations often can be coordinated with the operations of infantry patrols if the trail net is satisfactory and such supporting troops are available in the area. Such coordinated efforts should be employed whenever possible to effect the seizure of important towns or localities along the river, or to increase the probability of inflicting a decisive defeat upon the hostile forces.

b. Aviation.--Aviation support is fully as important for the successful conclusion of river operations as for the corresponding land operations. For details, see Chapter IX, "Aviation."