Operation of Stations_
The capture of messengers is no longer the only means available to the enemy for gaining information as to the plans of a commander. All radio messages sent out can be copied at hostile stations within radio range. If the enemy can get a fine wire within one hundred feet of a buzzer line or within thirty feet of a telegraph line, the message can be copied by induction. Messages passing over commercial telegraph lines, and even over military lines, can be copied by spies in the offices. On telegraph lines of a permanent nature it is possible to install high speed automatic sending and receiving machines and thus prevent surreptitious copying of messages, but nothing but a secure cipher will serve with other means of communication. >> 39-94-01-01
At signal stations where continued operation is required at least a squad or "set of fours" is required. Physical and mental exhaustion always result from continuous signal duty, and as alertness of mind and body is an indispensable factor in the prevention of errors, two reliefs of signalmen should be furnished each station whenever practicable. The senior officer or enlisted man is in charge of the station and is responsible for efficiency and discipline. He will require from each man a strict and entire attention to his own immediate duties, and permit no conversation that will distract the men at work. He will be careful not to allow persons to loiter about the station or within the hearing of the words called out to the signaler. The assignment of men should be such that a continuous watch for signals is kept and the responsibility for neglect to promptly answer calls determined. Of the station men, one is the sender, whose duty it is to transmit all signals to contiguous stations. Another, the receiver, attends the telescope and reads and calls off the signals displayed at the distant station. A third man acts as recorder, alternately calling off the outgoing message to the sender or transcribing the incoming message repeated by the receiver.
>> Calls and Personal Signals
Each station will be assigned a call consisting of one or two letters. Each and every operator will also have a personal signal of like character. Station calls or personal signals when once given or assumed will not be changed except by order of higher authority. Every station should at all times have on hand a list of all calls and personal signals liable to be encountered in station working. The general call suited to attract the attention of any station whose regular call is unknown will always be a signal represented by the letter "A" in the Morse or the letter "E" of the Army and Navy Code.
>> Opening Communication
To open communication with any distant station whose call is known, signal the call repeatedly, occasionally signing the call of the home station. If the regular call of the station sought is unknown the general call above prescribed should be used. As soon as the call is observed the called station will acknowledge receipt by "ii ii," or "I understand," signing thereafter its station call. These preliminaries completed, the stations are ready for working.
It is sometimes difficult to secure the attention of stations at unexpected hours. The force may not be strong enough for an uninterrupted watch. To provide, so far as possible, for this contingency, it may be concerted that if communication is required at unusual time, or is of pressing importance, certain flags shall be displayed, rockets discharged, smokes shown, or other attention-compelling signals used.
When a number of stations are in view from one station and it is desired to send a message to all or more than one station, some preconcerted signal, as a rocket, a red light, or some peculiar flag or torch signal, should be designated as a signal for general attention. Upon noticing this signal all the called stations reply, and then observe the calling station. This plan is useful when two or more stations can, at the same time, read the signals from the one station, and thus together receive any information to be transmitted from it.
When a signal station is to communicate with two or more stations, a telescope should be firmly fixed bearing on each, when practicable, and so far apart that those communicating with one station will not disturb the other party.
>> Commencing the Message
Every message is invariably commenced by the signal "Hr" or "Anr." Sometimes at the commencement of communication a preface will be sent in order to give some preparatory information to the receiving station regarding the number or character of messages about to be sent. For example, "Hr 8," means "I have eight for you" or "Hr ck 300" means a three hundred word message follows.
>> Sending and Receiving
Before the commencement of a message, care should be taken that all the letters and characters thereof are entirely and correctly understood by the signalman whose duty it is to call the same to the sending operator. The message is read off by the "reader," who first calls off a word and then spells it out letter by letter. The "reader" should observe the signals of the operator and invite his attention to any apparent errors. When the last letter of a word is announced this fact will be communicated to the sending operator.
At the receiving station the man at the telescope will call off each letter as received and not wait until the completion of a word. On reaching the end of a word announcement of this fact will be made to the recorder.
If the sending operator discovers that he has made an error which will probably render the sense of the message unintelligible at the receiving station, he will make the signal "BK" and recommence the message, beginning at the last word correctly sent. When the receiving station fails for any reason to get correctly what is being sent, the sending station is interrupted by the signal "GA," followed by the last word correctly received. The message will then be recommenced by the sending station at the point indicated.
>> Discontinuance of Transmission
When all the messages on file at any station have been sent the signal "NM" in Morse or "Cease signaling" in the army and navy system, according to which code is authorized, will be the concluding signal of the sending station. When a signal station is operated only during the daytime, the signal "GN" will be transmitted after all business filed up to the hour designated for closing has been dispatched.
>> Acknowledgment of Receipt
No message will be considered sent until receipt for the same has been acknowledged. This is effected by making either the "I understand" of the army and navy or the "OK" of one of the Morse systems, depending upon the one authorized. In every case the receiving operator's signal is signed after acknowledgment. When a number of messages are continuously sent, one acknowledgment for all will suffice and will be so understood. In receiving messages nothing should be taken for granted and nothing considered as seen until it has been positively and clearly in view.
>> Station Records
Records kept at field signal stations will be confined to original files of messages sent and carbon copies of messages received. Ordinarily the only available stationery will be the United States Army Field Message Book. Station records will be invariably preserved as part of the station equipment until orders for their disposition are given by higher authority. Whenever a station is in imminent danger of capture, all records should be destroyed in the discretion and under the direction of the operator in charge.
>> Formation of Signals
Make signals with regularity; do not send one word rapidly, the next slowly; adopt such a rate of speed as can be read by the distant signaler without causing him to "break" frequently. Make a distinct pause between letters. It is time gained to do so; it is a loss of time and an annoyance to run letters together. Nothing so distinguishes the good from the indifferent operator, visual or telegraph, as this. When signals are being made with a flag, a fraction of a second will be ample. In using the lantern or heliograph, the pause between letters should be relative to the time of display of the elements, longer than with the flag. To prevent any entangling of the flag upon its staff, skillful handling, acquired by practice, is necessary. It is accomplished by making a scoop of the flag against the wind, the movement describing an elongated figure 8, thus ∞. The motions should be made so as to display in the lateral waves the whole surface of the flag toward the point of observation.
In using the heliograph, if the receiver sees that the sender's mirror needs adjustment, he will turn on a steady flash until answered by a steady flash. When the adjustment is satisfactory, the receiver will cut off his flash and the sender will resume his message.
>> Repeating the Message
It may happen that very important messages received by signals must be verified by repeating back from the receiving station, signal by signal, each signal used by the sending station in conveying the message. There can be no error in signals thus verified, and the correct transmission of the message is made certain. For such verification each signal must be repeated by the receiving station as soon as it is made at the sending station.
>> Signal Practice
Full efficiency of the signaler can be maintained only through constant practice, and those in charge of Signal Corps troops should see that sufficient practice be had to insure that accuracy and rapidity in handling messages which is so essential in time of war.
Instruction should commence with the study of the principles of signaling and the theories of their general use, and the pupil should be well grounded in this study before practice is begun. He should so memorize the alphabets to be used that no letter combination will require thought to determine its meaning.
Daily inspections should be made to insure that all signaling instruments, appliances, and materials are in readiness for instant use. Defects in the apparatus annoy the sender; to a greater extent they annoy the person to whom the messages are imperfectly sent, and delays result that may have serious consequences.