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A US Navy crewman signals the letter 'U' using flag semaphore during an underway replenishment exercise (2005). Flag semaphore (from the Ancient Greek σῆμα (sêma) 'sign' and - φέρω (-phero) '-bearer' [1]) is a semaphore system conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands.
To avoid having to carry multiple sets of signal flags, the Code uses three "substitute" (or "repeater") flags. These repeat the flag at the indicated position. For instance, to signal MAA ("I request urgent medical advice" the Mike, Alfa, and 2nd substitute flags would be flown, the substitute indicating a repeat of the second character.
Flags may have individual significance as signals, or two or more flags may be manipulated so that their relative positions convey symbols. Flag signals allowed communication at a distance before the invention of radio and are still used especially in connection with ships.
Naval flag signalling undoubtedly developed in antiquity in order to coordinate naval action of multiple vessels. In the Peloponnesian War (431 – 401 BCE) squadrons of Athenian galleys were described by Thucydides as engaging in coordinated maneuvers which would have required some kind of communication; [1] there is no record of how such communication was done but flags would have been the ...
International maritime signal flags are various flags used to communicate with ships. The principal system of flags and associated codes is the International Code of Signals . [ 1 ] Various navies have flag systems with additional flags and codes, and other flags are used in special uses, or have historical significance.
A system like flag semaphore, with an alphabetic code, can certainly send any given message, but the system is designed for short-range communication between two persons. An engine order telegraph , used to send instructions from the bridge of a ship to the engine room, fails to meet both criteria; it has a limited distance and very simple ...
As well as digit flags, the code used "repeat" flags so that only one set of digits was needed; thus the word do, coded as "220", used a "2" flag, a "first repeat" flag here serving as a second 2, and a "0" flag. [12] The end of the message would be indicated by an "end of code" flag (blue over yellow diagonally split). [10] [12]
Semaphore (lit. ' apparatus for signalling '; from Ancient Greek σῆμα (sêma) 'mark, sign, token' and Greek -φόρος (-phóros) 'bearer, carrier') [1] is the use of an apparatus to create a visual signal transmitted over distance. [2] [3] A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms.