"A Manual of Signals: For The Use Of Signal Officers In The Field."
Washington, D.C., 1864.
TO DEVISE SIGNAL CODES.
"Two parties, each perfectly conversant with the principles of signals, coming in view of each other, can converse by signals, though there may be no pre-concert as to any particular code, or even as to the number of elements to be used in the code they will then devise, and none as to the particular signals they will use. This is done as follows: one party, having attracted the attention of the other, as by waving his handkerchief or his arms, or running continually to the right or left of a fixed position sees, by an answering signal, that he is noticed. This answering signal is made by repeating some sign in couplets, as by waving the handkerchief twice to the left at a time, for a number of times, or by making short runs, two at a time, to the left of any fixed position, or by any sign; only it must be repeated twice at a time, with a pause between each repetition. These double signals are always signals of recognition. The first party seeing this answer, acknowledges it by making signs of some kind of twos. These signs must be of the kind he intends to use in the conversation to follow. He then makes, slowly and very distinctly, six times, the signal, whatever it may be, he wishes to have read as "one," or the first element, and stands at rest. This is carefully noted by the second party, as the signal he is to read as "one," or the first element. The first party then makes, slowly and distinctly, six times, the signal he wishes read as "two," or the second element, and again pauses and stands at rest. This is noted by the second party, as before, to be read as "two," or the second element. The first party now makes, three times, the signal he intends to use for the "pause-signal," or end of a word, and stops. It will be seen, that two elements and a pause-signal have been indicated. These are sufficient with which to construct a code. The second party, having distinctly seen and noted these signals made, now makes the signal of recognition as before, then pauses and stands at rest, then makes, in his turn, six times, the signal he intends to use as "one," or first element, then pauses, then makes, six times, the signal he intends to use as "two," or second element, then pauses, then makes, three times, the signal he intends shall be his pause-signal. If possible, the signals made by the second party must be, for each, some numbered element-signals, similar to those used by the first party. When this is not possible, any other signals may be used.
The more simple and distinct the signals the better. Each party now knows the number of elements the other party proposes to use, the elementary signals by which those elements are to be indicated, and the pause-signal. In this case of illustration, two elements have been indicated. The parties can now converse by an alphabetic code of two elements mutually known to them, using these indicated signals in their proper places for the elements of that code. But if there has been no agreed alphabetic code, then to converse, these further rules are used. The first party shows a signal alphabet; that is, he makes slowly, with pauses between them, any twenty-six different combinations of the signal elements he has shown. These combinations are to stand for the twenty-six letters of the alphabet.
If the combinations are to be of motion-signals, the motions must follow each other without perceptible pause between them, until each letter combination is complete: there must be a pause of time to evince that this letter is finished. If the combinations are to be of stationary signals, each letter-combination must be a pause of time to evince that this letter is finished. If the combinations are to be of stationary signals, each letter-combination must be indicated as completed by making the pause-signal before commencing the next letter. Time must, in any case, be allowed for each letter, to permit it to be noted by the observer. The second part notes down these twenty-six letter-combinations, one by one, with his pencil, each in the order in which it is made, writing for each element signal shown its proper number, as the twenty-six letters of the alphabet follow each other in their usual sequence. So the record might stand as thus: a is 21, b is 22, c is 12; and so on, to the letter z. If the receiver doubts the signal for any letter, he makes signals for the sender to stop, and then makes, with his own signals, as they have been before agreed upon, the element-numbers of last letter correctly received. The sender now commences again at this last letter, and repeats that of which there has been doubt. The first party having thus sent the whole alphabet which it is his intention to use, makes the signal for completed message; that is, three pause-signals together, and awaits the reply. The second party, having clearly seen and correctly noted, in figures, each letter signal of this alphabet, now makes the recognition-signal, to indicate that he has understood it; and then, in his turn, using his own signals, he makes the twenty-six combinations he has received, and in the same order he has received and noted them; that is, in the usual order of sequence of the letters of the alphabet. He closes with the signal for completed message. To this, the first party replies with the signal for "signal seen and understood," and the word "correct." The second party, noting this message, replies with signals for "signals seen and understood," and the word "correct." The parties have now exchanged the alphabet, and have verified it. They have given to each other the combinations to be used for each letter, and the signals to indicate these combinations. Of course messages, of any kind, can now be transmitted. In this illustration, the alphabetic-code has been supposed to be of two elements; for the reason that this is most commonly used, is the most simple, and can be so invariably applied. If the parties are to use the ordinary signal flag, it will be now readily understood how they can, without any alphabet, code, or pre-concert open, at any time, communication. Alphabetic-codes, of any number of elements, may be formed whenever skilled signallists are visible to each other, by processes similar to the one described. This being the rule: that, so long as the signallist makes each signal six times, he is indicating the elementary signals he intends to use; and these elementary-signals are designated by the observer as the first, second, third, fourth, and so on, elements, according to the order of the sequence in which they are exhibited one after the other. The alphabets are then devised, to consist of two, three, four, or more elements, as the case may be. The pause-signal alone is made three times; and when it is made, it indicates that all the elementary-signals, to be used in the alphabet it is proposed to devise, have been shown. Thus, if two different signals are shown, each six times, and are followed by a pause-signal, made thrice, it is indicated that the alphabet to follow will be of two elements. If three distinct signals are shown, each six times, and are followed by a pause-signal, made thrice, the alphabet is to be of three elements; if four distinct signals are made, each six times, and are followed by a pause-signal, made thrice, the alphabet is to be of four elements; and thus on for any number of elements. This power of extemporizing alphabetic-codes of signals, of any order, and with any kind of signals, without pre-concert, other than acknowledge of general rules, and the possibility of so opening, at any time, anywhere, telegraphic communication between persons who may never have met, and may never meet more nearly than they are when thus conversing by signals, may be of use in a thousand contingencies of the service. For military uses, it has this advantage: that, if the parties are in sight of each other and at liberty, and can be protected, no human power can prevent their communication. It is available for beleaguered forts or cities, or vessels in distress, when communication cannot be had by boats, between any persons who, for duty or for pleasure, may wish to communicate at a long distance. Of course, it can be used with any apparatus or any mode of making signals, which has been described, or is conceivable. It can be used with day or with night signals, or with signals by sound.
With these rules known, the alphabet, and the dictionary of any language, given messages may be sent, and those may converse whose different nationalities would render conversation, by speech, impossible. The signal alphabets being once agreed upon, by the rules just given, each signallist finds, in the signals seen by him, and standing for letters and words, the letters and phrases of his own language; and when he signals in return, he makes, with his signals, the letters and the words of the language of his correspondent. An American, in distress, might thus signal intelligible messages on the coast of Russia, or of France, to the natives of those countries. Or two foreigners, coming in sight of each other, might converse, understandingly, by messages thus written in the air: for to signal by aerial signals, is virtually to write letters in the air, when neither of them would be able to comprehend the spoken pronunciation of the words that had been thus transmitted. The dream of a universal language is perhaps as nearly realized by these simple devices, as in any way hitherto suggested.
STATIONARY AND PERMANENT SIGNALS.
It is sometimes necessary to use permanent instead of transient signals, or signals made by placing objects in positions instead of in motion. This may be done to deceive an enemy who, having some clue to signals by motion, is entirely thrown off by permanent signals, or signals by position, though the signals made may be in reality identical when reduced to their elements and their combinations; or the change may be to rest men who are wearied by the labor of motion-signals; or the position may be such that signals of position are, for some reason, preferable. The rules for making signals by position, are the same as those which have been given for making signals by motion; only instead of 2, 3, 4, 5, etc., motions, each of which stands for an elementary-signal, there are 2, 3, 4, 5; and so on, positions which may stand for an elementary-signal, the signal object being to make each element placed in that position which indicates the proper number for that element, and there held until it has been recognized. In making signals by position, it is customary for each receiving station to repeat each position-signal as soon as it is observed, and at the sending station each signal, when made, is kept in position until it is thus recognized.
In rapid working, it is not absolutely necessary that this should be done. It is sometimes the case, that signals, by position, can be better hidden from the enemy, that those by motion, and that, for this reason, the signallist is less exposed to an enemy's fire while making them. A practiced signallist, should accustom himself, by considering supposable emergencies, and by devising plans of signalling for each emergency, and by practice in the field, when this is possible, to render available for signalling, all kinds of common things by which he finds himself surrounded; and to practice, using these things and conversing with signal codes of different numbers of elements, orders, and classes of signals, with transient and permanent signals, and in the use of ciphers, until he has made himself so skillful that he can, at any time, devise a mode of conversation, and carry on that conversation in such a way, that an enemy cannot decipher it.
Permanent signals may be used with semaphores, made on a flag-staff, or with the most simple structure and of work. The human figure, light clad, so as to show prominently on a dark ground, or when exposed against the sky, makes, with its movable arms, one of the best semaphores. Thus a man, with his coat off, is an upright with two movable and jointed arms. There is hardly any kind of position-signals, but can be made by placing the arms of this man in different positions. This human semaphore is visible, and the signals made by it are legible, with a good telescope, for a number of miles. To make the signals more distinct at a great distance, white discs, or flags, brilliantly colored staves, or any showy object, may be held in the hands."