FIELD MANUAL FM 72-20 – October 1944

General

Tactical operations in jungle terrain do not vary in principle from those under any other conditions. There are, however, certain differences in their application resulting from the conditions peculiar to jungles.

a. Movement in the jungle is often calculated in terms of time, rather than distance, the problem being how long it will take to get from one place to another, rather than how many miles it is between those places. Because of the poor quality of trails, their insufficient number, or their complete absence, and the difficulties of the terrain, the movement of troops is slow. Generally there can be no movement of tracked or wheeled vehicles larger than the 4¼-ton truck until engineers have improved the tracks and trails.

b. Flank security elements cannot maintain a fixed rate of march when operating off trails in thick jungle; their rate of movement, and consequently that of the column, is slowed by the necessity for cutting a trail; and the noise of their cutting may warn the enemy of their approach. Flank security of a jungle column is usually maintained by sending small detachments out a short distance on each side of the trail to listen and search for the enemy. These detachments withdraw and rejoin the tail of the column as it passes.

c. Supporting weapons and ammunition cannot be moved over jungle trails at the same speed as that at which ground troops move. If artillery is required to move over trails to support jungle operations, the speed of troop movement must conform to the speed at which artillery can displace.

d. Primary means of supply may be by air drop, carrying parties, pack animal, boat, or canoe. All have been used with success, but each has its limitations.

Observation

The dense foliage greatly restricts all observation. In many cases visibility is limited to as little as 20 feet. This makes contact and control one of the most difficult problems of jungle warfare, and considerably increases the responsibilities of small-unit leaders. Limited observation necessitates narrow frontages, reduced distances and intervals between units, and increased patrol activity and use of liaison parties. It increases the opportunities for ambush and the achievement of surprise small-arms fire. The difficulties of observation greatly restrict the use of supporting units and weapons. Indirect fires frequently must be adjusted by means other than direct observation of burst. The limitations of observation may be partially overcome by means of greater use of observation posts and increased communication facilities.

Transport

Vehicle operation for the most part is restricted to coastal regions and around plantations where adequate roads and wider trails are available. Pack animals may be used, but they require care and necessitate food for their own subsistence. Trails suitable for pack animals frequently are also suitable for operation of ¼-ton trucks. However, hand-carry is the principal means of transport. Native carriers are used for this purpose when available, but are subject to the limitations.

Communication

All organic means of communication are employed where appropriate. Telephones have proved Very serviceable; even patrols sometimes lay wire. The usefulness of radio is reduced by the screening effect of foliage and ground masks. Visual signaling is limited by the vegetation and the overhead canopy of trees, but smoke, lights, and pyrotechnics may be used by careful planning. Prearranged sound signals are important to security detachments. Foot messengers remain the major means of communication; these must be men of stamina and resourcefulness, who can work their way with assurance through the wilderness or along troop columns on narrow trails, and deliver their messages. Subordinate leaders must assure a constant flow of combat information from front to rear.

Fields of Fire

Because of the undergrowth and rugged terrain, good fields of fire are seldom obtained. Ideal firing positions are almost never to be found. Machine guns and automatic rifles seldom have fields of fire extending more than 100 yards; about 50 yards may be considered the average. Fields of fire for individual riflemen are even more restricted.

Concealment

The jungle provides ideal concealment for both offensive operations and for defensive positions. For this reason, surprise is always possible. The undergrowth and the dim light favor stealthy movement of attacking forces to assault positions. Similarly, exact “fixing” of enemy defensive positions is most difficult.