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"A Manual of Signals: For The Use Of Signal Officers In The Field."
Washington, D.C., 1864.
Part II
" TO WORK SIGNALS IN THE FIELD."
"To select a Signal Station.---The signals used in the field, Army of the U.S., are almost always those made with flags and the regulation signal equipment. Discs, although not visible at such great distances, may be used whenever the occasion requires it.
To select a signal station, choose a point perfectly in view of the communicating station; fix the exact position in which the flag-man is to stand: so arrange, if possible, that he will have behind him, when viewed from the communicating station, a background of the same color for every position in which the signals may be shown. The color of the background of a station is that of the earth or sky, against which the signals made seem to be displayed when viewed from the communicating station. For this purpose take the direction of the communicating station, and by going in front of your station, examine the position from that direction; ascertain whether the communicating station is higher, lower, or on a level with your own. If it is higher, the back ground for your signals, viewed thence, will be the color of the fields, woods, etc., behind and lower than your flag-man. If it is lower, your backgrounds will be the color of grounds, etc., behind and lying higher than your flag-man. If the stations are of equal elevation, then the back ground for your signals will be that directly behind the flag-man. Do not presume the back ground is of the color of the fields near you. It may be that of the woods a long distance, sometimes miles, behind your station. If your station is on a house or an eminence, it is still very possible, that there are higher grounds somewhere behind it. The color of back grounds is generally dark. Sky-exposure back grounds are rare. They are not often found at long ranges on land. They cannot be had except on the exact crest of ridges or lands which bound the horizon of view from the other station, or on the precise apex of mountains, etc. At short ranges, they may, of course, be had by working on the tops of very high buildings, steeples, etc. Unless certain of the color of the back ground, it is safe to presume it is not the sky, and that it is not light. It is a rule always to use the white or red flag until the color of the back ground is determined. The best back grounds are darkly colored, as green fields or woods.
Place the flag-man so that his signals shall appear displayed upon one of these back grounds if possible.
If the position is narrow, and the flag-man can be placed in no other, notice whether the back ground is broken: that is whether in part of its motion the flag, or other signal, displays on light and in part on dark back ground; as if, for instance, for half of its motion it shows against the trees, and for the other half against a white house; or if, for part of the motion, it shows against the sky, and for the rest, against trees.
The back ground being determined, the choice of flags is fixed. The color of the flag must contrast as strongly as possible with that of the back ground. This is important. Upon this contrast, the legibility of the signals often depends.
With green or dark, or any earth-colored back grounds, the white flag must be used. With a sky exposure, the black flag must be used. With broken, or mixed back grounds, the red flag must be used. The red flag, or signal, is that to be generally used at sea, as on vessels where, in part of its motion, the flag exposes against the wood work, or rigging, or sails, of the vessel; and in part against the sky or water. It is well also to try the red flag when snow may form part of the background. For general uses, the white flag, or signal, will be found best. It can be used in nine instances out of ten.
When the stations have commenced communicating, each can announce the color of the flag which can be best seen at the other. This can be done as soon as communication has commenced, each station telling the other to use the white, or the red, or the black flag, or to try different flags, until the best is found.
When it is difficult to attract attention, two flags ought to be shown on the staff at the same time. If there is doubt as to the color of the back ground on which they are displaying, these flags ought to be of different colors; as a white and a red. When the back ground is certainly dark, they ought to be both white. If the back ground is light, dark flags ought to be used.
Sometimes, when it is very difficult to send a message from a station, as happens occasionally, when detached clouds are passing the sun, and dark, moving shadows are thus thrown on the earth, the messages can be sent if the signals are made only while the sun is shining on the flag. This is particularly the case so long as the sun is in any part of its course only a little in front of the flag, and its light can be reflected.
Those days are best for the transmission of messages in which the atmosphere is clear, but the sun is covered with clouds. The light is then generally diffused. It is on such days that messages have been read at the longest distances.
On days of sunshine, the sun shining upon a flag, of course increases its visibility. The sun shining behind a flag, does not render it more distinct.
To Locate Stations.---To open a line of stations across a country, first choose some prominent position, and one well visible; and here establish the initial station. Let the party assemble here. Let them, together, select a second prominent point in view as nearly as possible in the line of direction you wish to take. Upon the first station, erect some kind of beacon: as a white or other colored signal flag; or some marked object, by which it can be recognized from a distance. Take from this first point, the bearing by compass of the point selected. This second point should be one not only visible from the initial point, but one also probably in view from positions beyond it. At the first point not marked with its beacon, station an officer to reply to any signals he may see, and to watch the course of the marching party. The other officers will then move, guided by compass, if need be, towards the second point selected, carrying a signal flag flying, in order that their position may be known whenever they come in view from the first station; and intently watched by the officer left at that station, the marching party will, from time to time, put itself in communication with the first station, so as to receive from it any direction as to its course the first station may wish to give, or any other information. It will also frequently verify its course by compass. On reaching the point chosen for the second station, a beacon or flag will be there erected, observations will be made, and communication will be opened with the first station. Points, on either side or rear, will be examined to see if the second station can be better located than it is with reference to a third station to be next established. The second station will then be definitely established and marked, and an officer there stationed, as before at the first station, to watch the marching party. The point for the third station will be hence chosen, and the party will proceed towards it with the same general rules as before. These operations will be repeated in the case of each station, until the terminal station is reached. Attempts intermediate stations by finding other a better points at which to locate some of them.
Should an officer, while establishing a line, and before it is completed find, on reaching any station, that he is able to communicate over any of the intermediate stations between himself and the first, he will notify the unnecessary station of the fact: not, however, until he has both received and sent messages over it to some other station. Upon receiving this information, the officers at the needless station will, after notifying the stations near them of their purpose, abandon their own station and proceed to the station next in advance, or to that one which has given the information. The officer who has been temporarily stationed there will, on their arrival, join the marching party, which will meanwhile have been pushed forward to continue the line.
In locating stations, and in opening communication between them, an officer will sometimes find himself in a position whence some other station ought to be visible, but finds his view shut off by trees or bushes near him. In this case, the tallest tree should be climbed. If the other station is in view from the tree-top, its attention can be attracted, and a temporary communication be opened, by signals made by the flag, or other signal, displayed in the tree-top. The flag-man may then secure himself in the tree with a belt or rope. The officer fixes his own position at some other place in the same tree, and rests his telescope among its branches; or what is better, ascends another tree for this purpose: as the first is opt to be so shaken by the motions of the flag-man, as to disturb the vision through the telescope.
It sometimes occurs in locating signal stations, that it can only be known that signal station will be opened in some part of the country overlooked from a given station; or that an officer has been sent in a certain direction, and that he will try, from some point in that direction, to open signal communication. It is well then to have some distinctive and very visible signals to attract attention. To mark position anywhere in an overlooked country by day, smokes may be made. Puffs of smoke, made by firing powder loosely poured upon the ground from cannon cartridges, can be seen at very great distances. These puffs may, to be distinctive, be varied in number. There should always be a pre-arranged code as to the number of puffs to be shown.
A station which has difficulty in making itself visible, will be apt to be discovered if it is moved too near where artillery is firing, the attention of the observer being drawn by the report and the smoke of the guns. A dense white smoke, visible at a long distance, can be made with dampened straw or hay. A fire should first be set well burning, and then large arms' full of the dampened straw, or arms' full of leafy branches, be thrown suddenly and well spread upon it. Cannon cartridges, with which to make smoke-puffs, can be easily carried on horseback; and can be fired with a train or other slow-match. Before a smoke-puff of any kind is made, the largest white and red flags ought to be displayed upon the signal flag-staff, and kept in motion, swinging from side to side, near the point from which the smoke rises, while it is rising, and for some time after, in order that the glass, at the observing station, turned upon the smoke, may find the flag thus moving in its field of view. When the attempt to attract the attention of the observing station is to be long continued, a large flag will be fastened to a second staff, and kept hoisted in some prominent position; the pole being fastened as in the corner of a fence, or to a stake driven into the ground.
Moving stations are those which may be opened anywhere at points not pre-determined. They are so called, to distinguish them from stations "fixed" by pre-concert. Moving stations must always be as prominently placed as is possible: as on hill-tops; in the centre of open fields; near marked houses,--the more apt to attract attention the better. It should be kept constantly in view, to always thus locate a moving station near something which is likely to attract attention from the observing station.
Officers upon signal stations will, if expecting signals anywhere, and habitually without especial orders, closely examine, from time to time, every prominent point within signal distance, to see if signal communication is from any quarter attempted. With this view, they will study the vicinity of all houses, spires, peaks, hill-tops, broad, open fields in the midst of woodlands(an open field commanding a view of a known fixed station, is a spot always to be selected in a forest, on which to establish a moving station); the banks of rivers, prominent trees, etc. The vicinity of smokes of any kind, seen at any time, must be most carefully scrutinized. At night all fire-lights, or brilliant lights of any kind, are to be examined. A signal-fire, made like any other fire, and meant to attract attention, is sometimes flashed to distinguish it from other fires. This is done by causing two men to hold a blanket spread before it: that is, between it and the observing station, and to raise and lower this blanket every two seconds. This is ordered in this wise: "one-two-up;" "one-two-down;" and continue. The intermittent light, thus made, is easily distinguished. The powder from cannon cartridges, poured loosely on the ground, and fired at night, makes an intense white flash almost certain to attract attention. Two or three cartridges may be employed together, and fired at one flash, to increase the volume of light. Rockets and roman candles are very useful. Composition lights, such as the coston signal lights, or the common red, white, or green composition lights are also useful. They will attract attention at distances of sic or eight miles. Red lights are preferable to any other, for the reason that they show distinct among camp fires, or other lights, and cannot be confounded with them. The volume of light may be increased for great distances by emptying the composition from several lights together, and thus firing it. Any kind of colored composition light may be agreed upon to be shown as a pre-concerted signal by which all friendly signal officers: as, for instance, those serving with a single army or a single corps, may indicate their position at night. During the whole time that these attention signals are making, by day or by night, the calling, or moving station, must watch closely with the telescope the station called; nor should the watch be relaxed, at any time, until communication is fairly opened. It can never be known at what moment the observing station may first have sight of, or be ready to reply to, the signal seen. Should the effort of the calling or moving station be successful, and attract the attention of the observing station, the observing or fixed station ought to reply at once with signals of recognition and a brief message: as "I see you," etc.; or, if it is practicable, it should make a signal similar to that seen: as answering smoke by smoke; a rocket by a rocket; composition lights by composition lights; or in fine, making some marked signal which shall announce to the moving station the fact that its position is noted. The observing station should take care to keep a signal flag flying all the time, to afford a marked point to the moving station, and to indicate that an officer is on duty and at the glass. The stations having recognized each the position of the other, telegraphic communication will be had without difficulty. It should always be borne in mind by an officer on signal duty, that it is very possible his own signals may be seen and read by the officer with whom he wished to communicate, though it may be impossible for him to find the exact position of that officer; or having found it, it may be impossible for him to read the signals made to him, owing to defect of light, or smoke, or glare, or haze. It is a rule, therefore, always to send any important message, or any information it is wished to convey, the sending station being in a position , as nearly as it can be judged, whence the signals ought to be seen by the other station. There is a chance, also, that some third station may receive the message, and the information be thus available. This is, or course, not to be considered as a final sending of the message, a message never being considered as sent, by signals, until it is clearly acknowledged by signals. This plan may, however, be sometimes useful. There are also, sometimes, intervals of two or three hours when the position of the sun, or a peculiar haze or light, makes one of two communicating stations almost invisible, while the other is thence seen more clearly than is usual. Now the visible station ought not to waste this time, but to send forward its messages with great care and distinctness, numbering the words, etc. This should not be attempted, however, unless the sending station is, while sending, always able to see at least the signals of recognition or "to repeat," made at the close of each message by the receiving station. As soon as mutual communication is had again, full inquiry can be made as to the receipt of the messages thus sent. So one officer may find himself so close to the enemy that he dare not respond to any signals, yet may perfectly read those made from another station. It may be important to send information by signals to an officer thus situated without caring to wait for his reply. There are other possible cases in which messages may be sent when it is known that they cannot be either acknowledged or answered by signals. A station may sometimes receive many messages when the messages sent by it cannot be read. It frequently happens that the signal of recognition, "message understood," and of "repeat, message not understood;" which two signals are sufficient to insure the correct reception of messages; can be seen, made by a station, when no consecutive signals made by that station are visible. Or a conventional signal, as a puff of smoke, may be agreed upon to indicate "messages understood," before the signal parties separate. Two puffs might mean "repeat;" or any other signal may be adopted. On the same principle, an officer calling a station with his flag, and being without reply, or with such replies only as he is unable to read, continuing to call, may interpose messages; for his flag is as visible and as likely to attract attention while sending a message, as while simply waving for attention. Thus such a message as this may be transmitted: "I cannot see you. Am going to the top of the mountain;" ir, "Can't see you. Look for me on the steeple;" or, "Can't see you. Go to open field on crest of ridge," etc.; or, "Can't see you. Enemy are coming by this," etc. This rule applies to night signals when, sometimes, one station distinctly sees the signals of another, but cannot reply with signals of the same kind, because the apparatus is broken, or the supply of fluid for the lights is exhausted. It, in such a case, a station is called, it replies by burning a signal light, or by throwing up a rocket, or by making a camp fire flash, or by flashing gun-powder: the message may then be sent. If it is correctly received, the disabled station shows two flashes, or throws up two rockets, or displays two lights. If the message is not correctly received, only a single flash, or rocket, or light, is shown. This indicates that the message must be repeated. A station can hardly be so disabled but that an experienced officer will be able to make this much of recognition. It is hardly possible he should be without some kind of light that can be seen, or the power to make some one of the numberless styles of signals.
A station should never be located in a camp, or among tents, or where the white canvas of tents can form the back ground of signals viewed from the other station. The passage of squads of men in an encampment, the smoke from the numerous cook-fires, the dust thrown up by marching troops or trains, the curiosity of persons not attached to the station, render the camp the most unsuitable locality for a signal station. The difficulties are increased, at night, by the glare of the numerous fires apt to bekindled between the communicating stations, the smoke that then more heavily than in the day, rests over the quarters, and the almost impossibility of distinguishing, at great distances, the signal-torches or lights from the changing-lights of the encampment. Every precaution should be taken to avoid these annoyances. The point chosen ought to be one sufficiently near the headquarters of the General Commanding, but out side of camp, and on one side of it, on some clearly visible spot, and with as few encampments between it and the communicating station as possible. It is always advisable to avoid working over en encampment, if it is near and on nearly the same level as the station. The smoke and dust which constantly arise from a camp, are serious obstacles to successful working.
Red lights or rockets must be kept at encampment stations, to mark the exact position of that station, if the communicating station is very far distant, and the officers at it thus liable to be confused by the number of lights and fires at the encampment. This will be found to be often the case, when the stations are located among the camps of a grand army."
