The Science Notebook
Gilbert Signal Engineering - Part 4

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NOTE:  This book was published in 1920, and while many of the experiments and activities here may be safely done as written, a few of them may not be considered particularly safe today.  If you try anything here, please understand that you do so at your own risk.  See our Terms of Use.   

NOTE # 2:  Some of the codes in this book have changed slightly.  For example, the International Morse Code, known at the time as the "General Service Code is still used today and is as shown in this book.  (See p. 15.)  However, some of the "conventional signals" have changed.  (See p 17.)  Learning to send or receive Morse code by sound, light or semaphore might be a little hard, but it can be a lot of fun, but before you attempt to learn it, be sure you are using the correct code and signals for today.  You should be able to get the current version of the code or sending method you want to use online.  Check out our Downloads and Useful Links pages for additional information.

Pages 76 - 100


The short piece of moulding is lettered with capitals starting with A at top, going down or the reverse of the lettering on the longer piece, which starts at bottom going up.

The number 10 on the small piece and the opposite number on the long piece are used as keys to cipher.

Method of Using Cipher Outfit. By referring to Figure 22 it will be seen at once that to change the cipher all that is necessary is to shift the small piece of picture moulding up or down. Each sending and receiving station would have this outfit handy, and to send a message the following procedure should be kept in mind.

Encipher or, that is, put your message into cipher from capitals to the opposite small alphabet.

To decipher a message at receiving station use the reverse method.

To give the receiver the proper key to cipher; this can be done by signaling the key in the preamble of your message; for example, the message : "WE BREAK CAMP AT SUNRISE" would be sent, if taken from Figure 22, as follows: (Key) 1027 QI LVIMC KMAX MT USZVEUI.


Chapter VIII

United States Maritime Signaling is divided into two branches: that of the Merchant Marine and that of the Navy. The signal methods of the Merchant Marine apply in all cases to privately owned yachts, power boats and other small craft having use for a signal system.

To be well versed in Maritime Signaling it is necessary for a signalist to know wherein the methods differ between U. S. merchant vessels and ships of the U. S. Navy.

U. S. Merchant Marine Signaling. The methods of signaling in the U. S. Merchant Marine are based entirely on the International Code of signals, which is the result of many years of work on the part of the International Marine Conference.

The International Signal Book is used by all vessels throughout the world, both merchant and men-of-war, thus enabling all ships to carry on communications by signals, even without the knowledge of one another's language.

Every signal in the International Signal Book has the same meaning in any language.

Signals are sent from the International Signal Code by means of the following systems :

Flag Hoists, International Morse Code, which is same as General Service Code, International Flag Waving, Colombs Sound and Flashing System and International Distance Signals.

The most general method of signaling by vessels is by means of flag hoists in which the International Code flags are employed.


There is nothing that gives a poorer impression to expert signalmen, or those who know, than to observe the misuse of flags in signaling. For this reason the writer will acquaint you in a general way with a few nautical terms relating to flag hoist signals and correct form of handling flags.


The Hoist of any flag is the side fastened to flagstaff or line holding it.

The Fly of a flag is at right angles to the hoist. (See Figure 23.)

A Hoist of flags is a number of signal flags on one line or hoist.

The lines by which a signal flag or flags are hoisted are called halyards.

That part of halyard which is attached to upper hoist of flag running through pulley or block is termed the down haul.

That part of halyard which is connected to the lower hoist of the flag or flags is termed the tail. (See Figure 23.)

Flag signals on merchant ships are usually hoisted to the most convenient position on the yardarm or mast from which signals can best be seen and distinguished.  However, on most of the larger ships a special signal

FIG. 23


FIG. 24

yard is used on the foremast which is situated ahead of the ship's funnels. The signals are not then obscured by smoke except in a case where receiving ship is dead astern.

Signal flags are flown from either Port (left side of a ship) signal yardarm, or Starboard (right side of a ship) signal yardarm according to position of the receiving ship.

A flag is said to be close up when hoisted to its limit on a yardarm or mast and at dip when only hoisted two-thirds of the way up. (See Figure 25.)

The Peak of a mast is extreme top point. All signal and special distinguishing flags vary in size and shape; however, in regard to shapes, a way of classifying as to proper names can be found by consulting Figure 27.

Signal flags are fastened on the halyards by means of a ring at the upper end of the hoist of flag and a snap hook at lower end. They may be tied to halyards by means of a single carrick bend. (See Figure 24.) The last method is clumsy and slow. All of the up-to-date merchant lines and navies that have a great many signals to handle use rings and hooks.


The International Code flags are twenty-six in number one for each letter of the alphabet and also a code pennant, all of which are pictured on Chart 10. (See special section of colored flags.)


One-flag signals B, C, D, L, P, Q and S hoisted singly have a special significance. The code pennant over each indicates that they are signals of a general nature and of frequent use.

Code flags hoisted singly after numerals signal Number 1 refer to numeral table in Code Book, as do also two-flag signals with code pennant hoisted under them.

Two-flag signals without code flag are urgent and important signals; with the code flag hoisted over them they are time, latitude, longitude, barometer and thermometer signals. Three-flag signals express points of the compass, money, weights and measures and also other signals required for general communication. Four-flag signals with a burgee (A or B) uppermost are geographical signals; with C uppermost they are spelling or vocabulary signals; with G uppermost they are names of men-


FIG. 25


of-war; with a square flag uppermost they are names of merchant vessels.

The following are meanings given single flags already mentioned :

B. Am taking on (or unloading) explosives.
C. Yes or affirmative.
D. No or negative.
L. I have (or have had) infectious disease aboard.
P. I am about to sail ; all persons report on board.
Q. Have clean bill of health, but liable to quarantine.
S. I want a pilot.

Single flags are sometimes used as signals from a towing ship to ships in tow; the meanings when used thus do not, however, correspond in any way to above signals.


Example : Ship A wants to signal ship B. Ship A will hoist her ensign (national colors) over the code pennant but not on the same halyard. If hoisted at same mast as succeeding signal the methods will interfere. As soon as ship B makes out the attention signal she will answer by hoisting the code pennant at dip; then ship A proceeds with signals, first hauling down the code flag, and when completed ship B acknowledges by hoisting the code pennant close up and leaves it there until ship A hauls down the hoist of signals after which she lowers it to dip, and awaits the next signal.

When ship A has completed her signals she hauls down the ensign and the other ship hauls down the answering pennant (code pennant).


All flag hoists are read from top down and never exceed four to the hoist.

In case several ships are in sight and ship A wishes to signal ship B, she will attract attention of B by either of two ways; the first, is to hoist B ship's distinguishing letters or, second, to hoist the two-letter signals which indicate direction the ship she wishes to call is traveling.

All vessels are supposed to display their distinguishing call letters when passing at sea.


When in consequence of distance, wind or weather preventing the code flags from being seen, an alternative method of signaling is used, which is known as distant signals.

There are three ways of making distant signals:

1. By means of the Fixed Coast Semaphore.
2. By means of square flags, pennants and whefts.
3. By means of cones, balls and drums.

Calm weather and when wind is blowing from and towards the receiving station are the reasons that make it difficult to make out the colored flags of the International Code. For this same reason the method of distant signaling by means of square flags, pennants and whefts is not as preferable as by the cones,
balls and drums. A wheft is any flag tied in center to halyards; therefore this system is mostly used.

Chart 15 gives the distant signal alphabet by balls, cones and drums.

The shapes are made by stretching canvas over pieces of light wood or metal forms, the canvas is as a rule then painted black.

The signals are made from International Signal Book and hoists are read from top down same as the flags.





For convenience in their use the shapes representing the letters have been arranged in numerical order. The letters A to G begin with one, the letters H to U begin with two, and the letters V to Z begin with three.

Distant signals by Fixed Coast Semaphore are made by a semaphore machine. The position of the arms indicate numbers which are translated from the International Signal Book. This method is only employed by shore stations and not by ships.


The International Flag Waving System is done by a single stick wigwag flag and the International Morse Code is used. However, the method of making dots and dashes is different from the U. S. Army and Navy Wigwag System.

The dot is made by a short sweep of flag over the head of sender and a dash by a long swing of the flag.


Chapter IX

The flag signal system of the Navy is in all probability the most important of all day signal methods. It has the advantage over the two-arm semaphore, either hand flags or machine method, and the wigwag which are the other day systems used by the Navy and which have already been explained.

The advantage of flag signals in the Navy is the great range and its adaptability to fleet manoeuvering and battle tactics.

The flag signals are made by hoists transmitting the Navy Flag Code, this flag code can also be sent by all the other signal methods used in the Navy.

When flags are necessary for intercommunication between the U. S. Army and all merchant ships, the International Flag Code is used.

The term "break" or flag is "broken" will come up in connection with Navy flag signaling, so it will be well to acquaint you with the proper way of making up a signal flag for breaking.

There are several ways to do this, but the following plan, if followed, will prove the most reliable :

Figure 26 (A) shows a signal flag lying flat on the deck ready to be made up for the "break." To do this the flag is folded on dotted lines 1 and 2 and then rolled towards the hoist as in B, after which the tail line is laid on top of rolled flag in form of a loop. The free end of line is then wrapped securely around the roll and over the loop by a number of turns and again looped into the end of other goose neck (see C) and drawn tight, which serves to clinch the tail line.


The flag is then ready to hoist as in D, after which it can be broken by simply giving a sharp tug on the tail line.

The foremast is principally used for signaling by naval ships, except in the case of a flagship which flies her signals from the

FIG. 26


main mast. The signal yards in either case are usually provided with three to six signal halyards on each port and starboard side. The peak of a mast on a naval ship is usually termed the truck.


The General Signal Book of the U. S. Navy contains a list of signals known as the Navy Flag Code. This book is divided into various parts, some of which are very confidential and are in the hands of only the higher officers.

The method of making the signals is alike no matter from what section or volume, as the meanings are arranged in alphabetical order opposite the signals to be sent.

The flags and pennants used in the Navy for making flag signals are the alphabet flags of the International Code flags, except the code pennant (see Chart 10) and a number of special flags and pennants contained in Charts 11 and 12.

While the alphabet flags of the Navy Code are same in design as those of the International Code, they have no connection whatever. A distinct naval feature is to call the flags by name rather than by letter, the name applied to the alphabet flags are able for A, boy for B, etc., same as the conventional signals used for telephoning on page 66.


Each ship in the Navy is furnished with a call, which is a combination of two letters like ZL, PN, or AD.

For sake of convenience the first letter of a ship's call represents the group to which that ship belongs and the second letter the ship of that particular group.

One set of flags is used for the group and another for the ship.


FIG. 27


The two-letter call of each ship is made by using one of the call flags and one of the call pennants. (See Chart 11.)

In order to furnish calls to squadrons, divisions, etc., of a fleet additional flags are used for indicator flags and will be found on Chart 12 under the title, Squadron, Division, Torpedo Flotilla and Submarine Flotilla.

The call of a particular ship wanted to take a message would be made (in case of a number of naval ships of various classes in immediate vicinity) by its indicator flag with call letters hoisted underneath.

Where a general call or message is to be given to all ships within signal distance, the cornet flag is hoisted without individual call letters and all ships are required to answer.

All naval vessels passing at sea always hoist their call letters. The answering pennant is used to answer all flag signals, and is hoisted from point best seen (at truck or either side of the signal yard) and is kept there until ship signaling hauls down the signal. The answering pennant is also used as a divisional point in making a numeral hoist.

The alphabet flags from Q to Z are designated as numerals from 1 to respectively and are so indicated when the numeral flag precedes them on a hoist.

The repeaters 1st, 2d and 3d serve to reproduce numeral hoisted above them. The first repeater would act as a repeater for the first flag, 2d repeater for second and so on. For example, the numeral 232 would be hoisted using the numeral flag followed by R(2), S(3) and first repeater.

The numeral 2222 would be hoisted R(2) 1st, 2d, and. 3d repeaters.

The Preparatory Flag (L) means prepare to execute signal shown. It is also used as a time signal by the flagship or senior ship present, in which case it is hoisted at 6:55 A. M. and hauled down promptly at 7 A. M. It also indicates that the


uniform of crew is same as yesterday. When hoisted at 7 : 45 A. M. over a numeral it indicates the size of the ensign (colors) ships are to hoist at 8 A.M. It is hauled down at 8 A. M. and all ships then hoist the national colors.

The Interrogatory Flag (O) hoisted over a signal changes its meaning into the interrogatory form.

The Affirmative Flag (P) when hoisted in answer to a signal means yes, or permission granted.

The Negative Flag (K) when hoisted in answer to a signal means no, or request not granted.

The Annulling Flag (N) annuls all signals at time display on the same mast, hoisted alone it annuls a previous signal which has just been made.

The Quarantine Flag (Q) hoisted at foremast truck indicates ship is under quarantine or has an infectious disease aboard.

The Guard and Guide Flag, when hoisted at fore truck in port between sunrise and sunset, indicates that that ship is charged with the guard duty for that day (a red truck light is used at night at foremast).

When hoisted by a ship under way it indicates that that ship is to guide the formation.

The guard flag is displayed on all the small boats belonging to the ship doing guard duty. The guard flag, however, is not displayed in any way by a flagship if they are performing that duty.

The Convoy and Position Pennant is worn at the foretruck of all ships on convoy duty; in formation, when hoisted at dip it signifies "I am temporarily out of position.'

The Danger and Designating Flag hoisted alone means danger ahead; a compass signal under it signifies the direction from which danger is expected.

The Dispatch and Breakdown Flag (I) when worn at main truck indicates that that ship is on dispatch duty; in fleet formation this flag is always kept rounded up ready to "break" at


foretruck and when "broke," it signifies a breakdown of ships machinery or the steering gear. In case of a man overboard it is "broken" and lowered at dip.

The General and Boat Recall Flag. Hoisted alone this flag calls all the small boats back to their respective ship at once. When hoisted under a number it recalls only that boat or boats having these numbers. At night small boats are recalled by the display of I followed by boat numbers and the call letters of ship signaling.

The Powder and Firing Flag (B) is displayed at the foremast of all naval vessels engaged in taking on board explosives, such as loaded shells, fuel oil or gasoline.

The Meal, Full Speed and Flag Officer Leaving Pennant, when hoisted singly at the port yardarm by a ship at anchor, signifies that crew is at meal ; if hoisted at sea on same yardarm with the speed cone, it means one knot faster than standard speed; alone with speed cone it denotes full speed; and when hoisted under the flag of any flag officer it conveys the fact that that officer is leaving the ship.

The Battle Efficiency Pennant is shown at the foremast (when ship is at anchor) of ship or ships which are authorized to fly same. The Battle Efficiency Pennant is awarded each year by the Navy to one ship in each of the battleship, submarine and torpedo boat class for excelling in gunnery and engineering for that particular year.

The Church Pennant is hoisted over the ensign while divine services are being held, it is the only flag ever hoisted over the ensign for any reason whatsoever.

The Red Cross Flag is an International flag flown by all hospital ships, their small boats and also flown at Naval Field Hospitals. The flag is flown at the bowstaff on ships.

The Submarine Warning Flag is hoisted and flown by any vessel or small boat acting as a mother ship or fender to sub-


marines, and it signifies that submarines are submerged or operating in that vicinity.


Every ship in the U. S. Navy carries a complete set of the various national ensigns of other countries. Some nations have two ensigns, each different in design, one for men-of-war and another for merchant vessels. In the case of the United States government the national colors are alike for both naval and merchant ships.

The national ensigns of foreign countries are flown from the main mast of U. S. Naval vessels on occasions such as a visit from the head of a foreign government or any other high officials, either diplomatic, military or naval. In American or foreign waters, on occasion of such a visit, the national ensign of the country the official represents is made up and "broke" at main mast as the visitor or visitors step aboard. At time flag is broken the saluting battery fires the proper salute that the visitor is entitled to.

U. S. Naval ships upon entering a foreign port always "break" the national ensign of the nation visited and fire a salute of twenty-one guns. The salute is answered by the highest official present from either a naval vessel or a military shore station or fort.

U. S. Naval ships passing other men-of-war or merchant ships at sea always dip the colors in answer to the same courtesies. It is customary for merchant ships of either U. S. or foreign countries to dip colors to the men-of-war first. However, in case of naval vessels meeting, the junior officer always dips first to his senior. No salutes are fired as a rule to naval officers of a rank lower than a flag officer, which in the U. S. Navy is a Rear Admiral or above in rank, except where an officer lower in rank may be acting in that capacity.



The time for flying of the national ensign on naval ships is given by the senior officer present. The size of colors to be used is also designated by signal. As a general rule the colors are hoisted at 8 A.M. in port and at the flagstaff at stern of ship with the proper ceremonies. At sea the colors are hoisted at the gaff (small spar projecting from the main mast). The colors are lowered at sunset with the same ceremonies, but at sea the colors are usually replaced after being lowered by a smaller ensign which flies all night, as do certain other special designator and personal flags. It is not customary to signal by means of flags before morning or after evening colors.

The Union Jack is hoisted in port only and at jackstaff in bow. It is hoisted at morning colors and lowered at evening colors. The Union Jack hoisted at fore signal yard indicates there is a general court martial or court of inquiry being held aboard. When hoisted for such purposes a gun is fired. The Union Jack hoisted at foremast truck calls a pilot aboard.


Chart 13 gives the personal flags of the higher officers in U. S. Navy, along with special distinguishing flags of the naval militia and yachts.

The President's Consular and flags of Secretaries of the Navy are used on any visit to a naval vessel by these officials.

The personal flags of Admiral, Vice Admiral and the Rear Admirals are flown at the main mast truck of their respective flagships.

The Blue Pennant of Senior Officer present is known by the ship having the senior officer of any group of naval vessels in the absence of a flag officer.

All naval ships in commission fly the commission pennant at


the main mast truck. This pennant really acts as a personal flag of the commander of the ship and in case of a flagship it is not worn, as the flag officer's personal flag signifies that that ship is in commission.

The Naval Militia Distinguishing Flag is worn at foremast truck of all naval vessels loaned by the Navy department to a state for use of Naval Militia or Naval Reserves when such vessels are under command of Naval Militia or Reserve Officers. The Naval Militia Commission Pennant is worn at main mast truck on such ships, and in event of ship having a flag officer aboard his personal flag is flown instead at main truck. The rank of Commodore is the highest in Naval Militia.


It is required by law that all pleasure yachts and boats of more than 15 tons display the yacht ensign. This you will note by referring to Chart 12 is different in design from the national ensign and serves to signify when worn that that particular ship is a pleasure boat.

Yachts fly all personal flags in a similar way as used in Navy. For signaling, they use all navy methods except Navy Flag Code. The substitute being the International Flag Code for flag hoist signals.


Chapter X


1. Upon the discovery of a wreck at night, the life-saving shore station burns a red light or sends up a red rocket to signify "You are seen," assistance will be given soon as possible.

2. A red flag waved on shore by day or a red light or red rocket by night means "Haul away."

3. A white flag waved on shore by day or a white' light waved slowly or white rocket by night means "Slack away."

4. Two flags a white and a red waved at same time on shore by day, or two lights a white and red swung slowly or a blue light burned by night signifies "Do not attempt to land in your own boats, it is impossible."

5. A man on shore beckoning by day or two torches burning closely together by night will signify "This is the best place to land."


Any of the following when displayed from a ship will call a pilot :

1. The Jack, hoisted at the foremast.

2. The International Code pilot signal indicated by the alphabet letters P T.

3. The International Code flag S displayed alone or with code pennant over it.

4. The Distant Signal, with cone pointed upward, having above it two balls or oval shapes.


5. At night, a blue light burned at intervals of about fifteen minutes or a bright white light flashed at short intervals just above the deck.

6. To signal for a tow boat place the National Ensign in main rigging just above the decks at intervals of one minute at a time.


1. A gun or other explosives fired at intervals of one minute.

2. The International Code letters N C.

3. Fog Signal apparatus sounded steady.

4. The Distant Signal consisting of a cone pointed upward, having either above or below it a ball or oval shape.


1. Gun or other shot fired every minute.

2. Flames of a burning tar or oil barrel.

3. Rockets or shells throwing stars any color at short intervals.

4. Foghorn sounded steady.

The United States Weather Bureau is operated under the Department of Agriculture. The Bureau has many stations throughout the country as well as 142 stations on the Atlantic and Gulf Coasts and 46 stations on the Pacific Coast.

Weather predictions are given out from these stations to all the newspapers, and bulletins are furnished to all Federal buildings for posting.

The inland stations have telegraphic connections with the coast stations and inform them of the approach of severe storms. The coast stations in turn notify mariners by means of flag signals and radio.


All the civilized nations of the world maintain a similar system in which their coast stations give information to ships.

The Weather Signal flags may be seen by turning to colored Chart 14; at bottom of same chart are storm and wind signal flags, along with night lantern signals.

The Weather and Storm Signal flags when displayed on a flag pole are arranged to read from top down. When single hoists of several flags are made on a signal yard a small streamer is used to indicate the point from which signals are to be read.

Temperature forecasts signals are made by using the weather flags, five in number four square flags and one pennant.

The flags are displayed at weather bureau stations as follows, and indicate weather predictions for next twenty-four hours, commencing at 8 P.M. of day the signals are made :

1. Square white flag indicates clear or fair weather.

2. Square blue flag indicates rain or snow.

3. Square flag white on upper half and blue on lower half indicates local rains or showers will occur and that rainfall will not be general.

4. Square white flag with black square center indicates the approach of a sudden and decided drop in temperature a cold wave.

5. Black pennant is used to refer to temperature and has no meaning hoisted alone. In no case is it ever hoisted with the square white flag with black center. (Cold wave flag.)

The black pennant hoisted above square white flag, blue flag and white and blue flag indicates warmer weather along with the regular indication that that flag stands for. When hoisted below any of these flags it means colder weather.

Storm and Wind Signals. The warnings adopted by the U. S. Weather Biireau to announce the approach of wind storms are as follows : (See bottom of colored Chart 14.)


The Small Craft Warning. A red pennant indicates that moderately strong winds that will interfere with the safe operation of small craft are expected. No night display of small craft warnings is made.

The Northeast Storm Warning. A red pennant above a square red flag with black center displayed by day or two red lanterns, one above the other, displayed by night indicates the approach of a storm of marked violence with winds beginning from the northeast.

The Southeast Storm Warning. A red pennant below a square red flag with black center displayed by day or one red lantern displayed by night indicates the approach of a storm of marked violence with winds beginning from the southeast.

The Southwest Storm Warning. A white pennant below a square red flag with black center displayed by day or a white lantern below a red lantern displayed by night indicates the approach of a storm of marked violence with winds beginning from the southwest.

The Northwest Storm Warning. A white pennant above a square red flag with black center displayed by day or a white lantern above a red lantern displayed by night indicates the approach of a storm of marked violence with winds beginning from the northwest.

Hurricane or Whole Gale Warning. Two square red flags with black centers, one above the other, displayed by day or two red lanterns, with a white lantern between, displayed by night indicates the approach of a tropical hurricane, or one of the extremely severe and dangerous storms which occasionally move across the Great Lakes and Atlantic Coast,


Chapter XI

Flag Making. The most suitable material for flag making is either galatea or calico. The color and dimensions of the cloth are dependent upon type of flag wanted and the size.

The tools necessary are a straight-edged yardstick or ruler, a soft pencil or chalk for marking off the cloth, an old safety razor blade or a pair of scissors for cutting and needle and thread for stitching flag together. You can get your mother or sister to do all sewing required on the sewing machine.

Making Wigwag Flags. The standard dimensions of the wigwag flags used by the Signal Corps are the 3-foot, 9-inch square flag with 12-inch square center and the 2-foot square flag with 8-inch square center.

The 2-foot size flag is large enough for most signaling and it will be best for you to adopt this size or possibly smaller as the larger type is only useful in case of extreme distances. The 12-foot staff necessary to carry a flag this large is very hard to handle.

The 2-foot wigwag flag needs a staff 5 1/2 feet in length. If flag is made smaller than this the staff can be made shorter and the center square can be cut down to a proportionate size.

The color combinations for wigwag flags are turkey red and white, or scarlet and yellow. Blue and white is sometimes used and is very good, but red and white is the best.

Flags can be made up using any of above combinations, alternating the colors of the body of the flag and center for use against different backgrounds.




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