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



Necessity for river operations		10-1
General characteristics of rivers	10-2

10-1. Necessity for river operations.-a. During the estimate of the situation, or after the initiation of the intervention, it may become apparent that navigable inland waterways exist within the theater of operations to such an extent that their use by the intervening forces necessary or advisable.

b. In many countries, water routes are a primary means of transportation and communication, especially if there are few and inadequate railroads, roads, or trails. In some sections of the country, they may be the only avenues of approach to areas occupied by hostile forces. So long as water routes are more economical in time and money than other available means, they will be employed by the local inhabitants and their use must be seriously considered in the plan of campaign of any force entering the country for small war operations. Such river operations as appear practicable should be coordinated with the land operations which are to be conducted simultaneously.

c. In some cases, it may be necessary or advisable to occupy a river valley in order to protect the foreign civilians of other than United States citizenship, and property located therein against hostile depredations.

d. When offensive operations against the hostile forces interrupt the normal land routes, such forces will turn to navigable rivers as a means of supply and communication, or as an avenue of escape. Adequate and timely preparations should be undertaken by the intervening force to deny these water routes to the enemy.

e. Navigable rivers often form part or all of the boundary between the affected country and an adjacent State. If the hostile forces are receiving assistance and supplies from the neighboring country, river patrols may seriously interfere with, but never entirely suppress, such activities. Amicable agreements should be completed soon as possible, through the Department of State, for the use of territorial waters by such patrols, and for the pursuit of hostile groups who may use the remote districts of the friendly country as a base of operations or place of refuge.

10-2. General characteristics of rivers.-All navigable rivers have certain similar characteristics. Their general profile is best represented as a series of terraces, the levels of which are relatively placid stretches of water of more or less uniform depth and current, and the walls of which are impassible falls or rapids. As one proceeds upstream from the mouth of the river, the depth of water in each successive level is usually less than in the one preceding. This characteristic feature determines the distance that a boat of any given draft can travel and eventually makes the use of any type of bent impossible. The extent of each group of falls and rapids, their relative distance from the mouth of the river, and the length of the intervening stretches of smooth water will vary with every river. For example, the first obstacle in the Congo River in Africa is only a hundred miles from its mouth, although the second level of the river presents no impassable falls for over a thousand miles. The Yangtze River in China is navigable by ocean-going vessels for nearly a thousand miles from its mouth before the Yangtze Gorge is reached. The Coco River in Nicaragua can be traveled for over 200 miles before the first real falls and rapids, extending over 30 miles, are found; the second level is navigable for some 60 miles; and the third level for another 70 miles to the head of navigation.

b. These various levels are customarily the "lower," "middle," and "upper" rivers as one proceeds upstream from the mouth to the head of navigation, and as the depth of water in the succeeding levels necessitates a change in the type and draft of boat which can be used.

c. The condition of the river, the depth and length of the navigable stretches, and the obstacles presented to navigation vary with the seasons of the year. At certain times, the water in the middle and upper rivers may be so low that numerous portages are necessary. when the river is in flood, such obstacles may disappear entirely and the boats normally restricted to the middle river may proceed all the way to the head of navigation, or the lower and middle rivers merge into one. This characteristic will influence the time of year and the ease and practicability of conducting river operations. The probability that supply boats could not reach Poteca, on the Coco River, during the months of April and May, influenced the decision to abandon that outpost in April 1929. In commenting on the Nile Expedition of 1884-85, Callwell says, "And it must be added that the supply difficulties were enormously increased by the lateness of the start, by the unfortunate postponement in deciding on the dispatch of the expedition. A few weeks sufficed to convert the Nile between the second and third cataracts from a great waterway up which the steamers from below Wadi Halfa could have steamed with ease, into a succession of tortuous rapids passable only with difficulty by small boats." ("Small Wars, Their Principles and Practice," by Col. C, E. Callwell, 3d cd., p. 70.)

d. As the river empties into the ocean, the sediment which it carries is deposited to form a bar or shoal. In the case of large rivers, the shoal is usually so deeply submerged that it does not prevent the entrance of ocean going vessels. In those rivers usually found in the theater of small war operations, the bar may be so near the surface of the water that it is a real obstacle and may make the passage of even the ordinary ship's boat a dangerous undertaking, especially if the services of a local pilot are not available.

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