The higher unit is responsible for the establishment and maintenance of communication with the next lower unit. Wire connection with neighboring units is always established to the unit on the right. This rule does not release the commanders of responsibility, however, to maintain contact with units to their left.

Of special importance is the connection between artillery and infantry. If an artillery unit is attached to an infantry unit, then the infantry is responsible for the connection; if the artillery is supporting an infantry unit, but not attached to it, then the artillery is responsible for the connection. If, however, the artillery, through some special circumstances, is unable to establish the connection, then the infantry must undertake the responsibility. Connection with heavy infantry weapons is the responsibility of the infantry commander concerned.

25. OPERATION OF SIGNAL COMMUNICATION TROOPS

The commander issues orders for the employment of his communication units ordinarily after receiving the recommendations of the communication officer. It is most essential that the commander punctually give the communication officer a complete picture of the situation, including the commander's intentions. The communication means of a command post are assembled in a message center. The proper functioning of communication is dependent upon its useful employment on the part of the commander and upon the technical training of personnel.

26. ORDER OF THE DIVISION COMMUNICATION OFFICER

The order of the division communication officer should contain: (a) The enemy situation, our own troops, the plan of the commander; (b) the mission of the signal battalion; (c) specific orders for the signal communication companies and supply train; (d) when applicable, instructions relative to secrecy, replacement, utilization of commercial nets, and system maintenance.

In the advance march, the division communication battalion builds and maintains an axis of signal communication (wire lines) along the route upon which the division commander and his headquarters are advancing. In friendly territory, the existing commercial net is utilized to a maximum; in enemy territory, heavy field cable is generally installed overhead. When contact with the enemy has been established by the division, wire communication must be maintained at all costs with the corps and must also be supplemented by radio and other means. Establishment of lateral connections within the division and between divisions is also very important in coordinating the tactical effort.

Within the division, all command posts and observation posts should be connected according to their relative importance. The division signal battalion will establish lines to the infantry regiments, artillery commander, and the artillery units operating under the artillery com- mander, as well as lateral connection to adjoining divisions. When there is a deficiency of means, the establishment of the aforementioned artillery connection has priority. The division signal officer will coordinate the establishment of the communication net and supervise its construction by his own signal troops and the communication troops of the various units. In a rapidly advancing attack, in pursuit, or in wtihdrawals or retreat, he will restrict the amount of installation.

27. COMMUNICATION IN THE DEFENSE

In the defense a very extensive communication net is established. Its construction is governed by the situation, and by the time, materiel, and personnel available. Several means of communication between all important defensive installations are provided. Wire communication is carried by buried cables. Special communication nets (such as infantry, artillery, antiaircraft) are established. Alarms for gas and air attacks are installed. Technical means to intercept hostile messages are intensified.

28. VARIOUS MEANS OF COMMUNICATION

When new troops are attached to a command, additional communication requirements are introduced; so reserve communication personnel should always be held out. The operation of communication troops must not be interfered with in any manner by other units. The various means of communication can be characterized as follows:

(a) Telephone.--Installation of the telephone requires time and matériel. Wire lines are sensitive to such disturbances as fire, wind, snow, frost, and storms. The enemy can easily listen in on conversations, particularly over single-wire connections; in the danger zone, therefore, double lines and heavy insulated wires are used.

(b) Telegraph.--The telegraph is simple in operation and installation, and very often cannot be easily intercepted. The Morse code is utilized.

(c) Automobile, mounted messenger, bicylist, motorcyclist, runner.--In a war of movement, these means are often the most reliable. They are used without hesitancy when technical means are not available. Speeds of transmission vary.¹⁰

(d) Radio.--When wire connections fail or are not functioning steadily, the radio is indispensable. Electric storms, static, other radio transmission on similar wave lengths, mountains, and other interferences minimize effective range of hearing. In practice, radio is valuable only if messages are short; transmissions should therefore be in telegram form, omitting all unessential words.

(e) Blinker.--This is an important signal means in battle when wire lines are destroyed. It cannot be used for great distances, and is greatly restricted by fog, mist, bright sunshine, or proximity of enemy observation. Blinker messages must be very short, since 20 words require about 10 minutes for transmission.

(f) Rockets, Very lights, flares.--These serve as signals whose meaning has been prearranged and is thoroughly understood by the troops concerned. Very pistols and pyrotechnic equipment are carried habitually on light telephone carts and also in all combat trains. Ability to see these signal lights is greatly influenced by the terrain. Also, there is always the chance of confusion with enemy signal lights.

(g) Signal flags and panels.--Prearranged signals with these means enable ground troops to send short messages, particularly in communicating with airplanes and balloons.

(h) Alarms.--Horns, sirens, bells, and gongs are used for gas or hostile airplane warning.

(i) Signal gun.--This small mortar, which projects a message container, is useful in position warfare.

(j) Courier pigeons.--Although requiring at least 3 days to orient, courier pigeons are useful under heavy fire, for they are sensitive to gas, and terrain does not influence them. They fly about 1 kilometer (5/8ths mile) in a minute. They do not fly in darkness, rain, or storm, and with snow it is difficult for them to orient themselves.

(k) Message dogs.--Expert and affectionate care by the men in charge of message dogs results in most satisfactory returns. Such dogs can be used under heavy fire, and can remember and find locations on a battlefield in a radius of about 2 kilometers (1 1/4 miles). They will efficiently follow an artificially made track (scent) up to 6 kilometers (about 4 miles).

(l) Listening-in apparatus.--This apparatus is established to determine the location of hostile activity in planting mines, and to listen in on hostile communications.

(m) Airplanes.--An airplane may be used to connect a division headquarters with its foremost elements or neighbor units. In such cases, no other reconnaissance mission should be given the plane. It is important to establish the location of the foremost line of infantry and of the hostile line; the infantry troops on prearranged signal will display panels to assist the plane on the mission. Planes may be used for artillery fire direction, and for maintaining connection between division, cavalry division, and corps or army headquarters. They are particularly adapted to distributing quickly important orders or delivering reports to units a considerable distance away.

(n) Captive balloons.--Balloons observe artillery fire, give prearranged signals indicating the time of the day, the signal to open fire, etc. Their communication means include flags, panels, blinkers, and telephones. Weather conditions, heavy-wooded terrain, and mountainous country restrict their usefulness.