The following, extracted from Notes On Naval Communications by Lt A. C. Kidd, USNI, 1924, has been contributed by Byron F. Angel (byron@trident-usa.com).
MEANS OF VISUAL COMMUNICATION
420. Boat flags are used during daylight on battleships in formation at sea to indicate the engine speed to the nearest knot. these are used in addition to speed signals, speed cones, etc., and are displayed at a low position to avoid confusion with regular signals.
421. When making signals by visual methods other than flag hoist, the procedure used is, with few exceptions, the same as that used in radio.
MATERIAL MEANS
422. Semaphore is used largely in despatch work in the fleet. It is rapid for short distances and is sometimes used to transmit signals from low positions, when flag or searchlight signals cannot be read on account of smoke. Wigwag is slower than semaphore, but can be read at a greater distance. It is employed extensively for ship to shore communications and on shore by landing forces. A good nbackground is essential for good results when using either semaphore or wigwag.
423. Yardarm blinker is rapid and very useful up to a certain point, but when the distance is great or the number is large or the formation is complicated, the yardarm blinker is not satisfactory.
424. High power search lights provide one of the most effective means of communicating by flashing light day or night. They are better suited for signals than for depatch work, for the reason that they are slow and do not function so well after they have been in use awhile and get very hot.
425. Blinker tubes are used chiefly for short range work, when it is desirable not to disclose the location of ships. They are directional and cannot be read by unfriendly vessels, unless pointed at the latter.
426. The Aldis signal light is a hand signal light with a pistol grip. The dots and dashes are produced by pulling a trigger which tilts a parabolic mirror and brings the search light beam to coincide with the line of sight through the sighting telescope or tube, which is mounted on the barrel. When the trigger is not pulled the beam is much higher than the line of sight and hence not visible to anyone on whom the telescope is sighted. An incandescent lamp of special design is used in the light. It burns continuously when the light is held by the grip, the circuit being closed by the pressure of the hand on a second trigger on the grip. A small storage battery supplies the power to run the lamp. This piece of apparatus is small, light, and efficient, and very useful for daylight signaling between vessels operating near each other, and between aeroplanes and ships or ground. The weight of the lamp is about 5-1/3 pounds.
WAR COLLEGE STANDARDS
428. The standard rules in use at the Naval War College represent what may be expected when employing the various methods of Visual Communications.
429. Standards are essential for all our activities and should be established for all methods. While at first they may be assigned arbitrarily, they should eventually represent actual performances, and any signal not up to standard should be investigates and the cause of delay remedied.
430. (a) Signals complete in one hoist, addressed by a commander to not more
than 8 ships of his command, including his flagship, all within easy tough (not more
than half the limiting distances), are transmissible in the following times,to vessels
not under effective fire:
By flag .........................................1 minute
By flash ........................................3 minutes
By semaphore and wigwag............8 minutes
(b) Signals under conditions other than the above, require:
By flag .........................................3 minute
By flash ........................................6 minutes
By semaphore and wigwag...........16 minutes
(c) Signals requiring division or squadron follow-the-leader movements need only be transmitted to division or squadron flagships.
(d) Vessels under effective fire require double these times to receive.
431. (a) Conflicting or alternative signals, such as "ships right" and "ships left", may not be made simultaneously or be pending at the same time.
(b) A tactical signal sent by any method, automatically annuls any conflicting signal previously made to the same force and not yet executed.
432. When making the executive sign, the text of the signal which is to be carried out is to be repeated before the executive sign if -
(1) There is any possibility of doubt to which signal the executive sign refers.
(2) When a second further signal requiring an "execute" is made before the "execute" sign is made for the first signal.
(3) When a considerable time has elapsed between transmission of a signal and the executive sign for that signal.
433. A signal of any kind made to a force not under the immediate command of the authority making it may be read by all ships within range, but if it requires action, it must be repeated by the immediate commander of the force affected before it can become effective, except in the case of division or squadron follow-the-leader movement.
434. (a) Despatches in plain language are transmissible in the following times (in minutes) to vessels not under effective fire:
(1) Sent by a commander to not more than 8 ships of his command, including his flagship, all within easy touch (not more than half the limiting distances):
For each group of 10 words or fraction thereof
By flash .......................................6 minutes
By semaphore and wigwag..........12 minutes
(2) Conditions other than the above:
For each group of 10 words or fraction thereof
By flash .......................................9 minutes
By semaphore and wigwag..........24 minutes
(b) Code despatches are transmissible in the following times (in minutes) to vessels not under effective fire (times inclusive of time to place message in code and to decode it):
(1) Sent by a commander to not more than 8 ships of his command, including his flagship, all within easy touch (not more than half the limiting distances):
For each group of 10 words or fraction thereof
By flash .....................................15 minutes
By semaphore and wigwag.........30 minutes
(2) Conditions other than the above:
For each group of 10 words or fraction thereof
By flash .....................................24 minutes
By semaphore and wigwag.........48 minutes
(c) Addresses and signatures not counted in the number of words.
(d) Vessels under effective fire require double the times given above.
(e) The above times also apply when sending a despatch via any U. S. Naval Shore Station.
435. Signals may be sent by any one of the following methods:
(a) Flag hoists (by day only).
(b) Flashing light.
(c) Pyrotechnics.
(d) Sound.
(e) Semaphore and wigwag.
Despatches may be sent by any of theabove methods except flag hoist.
436. (a) the following number of flag hoists may be flying simultaneously:
From large vessels........................5
From int. vessels............ ..............4
From small vessels........................2
From subs (surface)......................1
(b) Flag signals may be made to two or more portions of a fleet at the same time, provided that no more than the allowed number of hoists be made.
437. (a) Vessels may handle the following total number of of flash, wigwag, semaphore communications incoming or outgoing, at the same time:
Sent by
Large combatant vessels................4
Int. combatant vessels....................3
Small combatant vessels.................2
Submarines (surface)......................1
Submarines (submerged)................0
Auxiliaries......................................2
(b) Communications may be sent or received by any method up to the limit of simultaneous numbers without regard to the number being handled by other methods.
438. The following are the limits of transmission, in thousands of yards:
Sent by----------------------Flash------Flag------Wigwag----Semaphore
Large combatant vessels......20..........10.........5............2
Int. combatant vessels.......20..........10.........5............2
Small combatant vessels.......8...........5.........5............2
Submarines (surface)..........5...........2.........5............2
Submarines (submerged)....... 0...........0.........0............0
Auxiliaries..................10..........10.........5............2
Aircraft......................5
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