Code letters or ship'scall sign (orcallsign)[1][2] were a method of identifying ships before the introduction of modern navigation aids. Later, with the introduction of radio, code letters were also used asradio call signs.
In 1857, theUnited Kingdom sponsored theCommercial Code of Signals for the Use of All Nations at Sea, which introduced four letter flag signal codes to identify individual ships.[3] The first vessel to be reported inLloyd's List by her letters was theMallard (LDPN), offDeal, Kent whilst on a voyage fromLondon toCalcutta,India.[4] The Commercial Code of Signals, c. 1900, was modified to become theInternational Code of Signals. By the 1860s, individual ships were being allocated code letters in theUnited States andEurope. From 1874, code letters were recorded inLloyd's Register as part of each individual vessel's entry in the register. Generally, code letters allocated to a ship remained with that ship, although there are known cases where new code letters have been allocated following a change of port of registry or owner. Code Letters were sometimes reallocated once a ship had been struck from the register, but no two ships bore the same code letters at the same time.[3] With the introduction of radio for communications, code letters were used also as radio call signs.[5]
Code letters used the twenty-six flags that represent the letters of the alphabet, plus the ten flags that represent the digits 0–9 also have been used.[1] The substitute flags have not been used for call signs.
Each flag represents a character. If the ship's call sign is "3EJH2"
(Panama Flag)[1] the seamen would not say "Three E J H Two". Instead, they would say "Three Echo Juliet Hotel Two" to avoid misunderstanding as each country's seamen have their own pronunciation of letters and during speech over radio letters can be inaudible.
If the call sign has four characters, the first character (or figure) corresponds to the country code for the ship's flag state. If the call sign has five characters, the first two characters (or figure plus character) correspond to the country code for the ship's flag state. The variations of four or five characters, due to being limited to 36 characters (26 letters + 10 digits) are not enough for all countries. TheSoviet Union used the first character "U" in its call signs: the cargo shipMetallurg Anosov had the call sign "USMW"
. If the ship changes her flag state, she must also change her call sign. For example, the shipHeinrich Arp: Code Letters "RDWL" (1923-34)
were changed to Code Letters "DHKV" (1934-45)
and from 1946 once more to a Soviet Union call sign. (unknown, but first character was "U").
An up-to-date edition of the book or computer's play-disk "List of Ship Stations and Maritime Mobile Service Identity Assignments", published byITU, must be kept on board each sea-going ship. The book lists all sea-going ships and their call signs in accordance with Article 19, Section III of theITU Radio Regulations.[6][7]
Some canals or narrow places have special requirements for the vessels to hoist their call sign flags during the transit through the area. TheSuez Canal was one such place with this requirement. Thanks to technological advances in the navigation abilities of marine craft, this action is no longer compulsory.[8]
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