International Code of Signals
The International Code of Signals (ICS) is an international system of signals and codes for use by vessels to communicate important messages regarding safety of navigation and related matters. Signals can be sent by flaghoist, signal lamp
Signal lamp
A signal lamp is a visual signaling device for optical communication . Modern signal lamps are a focused lamp which can produce a pulse of light...

 ("blinker"), flag semaphore
Flag semaphore
Semaphore Flags is the system for conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags; it is read when the flag is in a fixed position...

, radiotelegraphy, and radiotelephony. The International Code is the most recent evolution of a wide variety of Maritime flag signalling
Maritime flag signalling
Maritime flag signalling, generally flaghoist signalling, is the principal means other than radio by which ships communicate to each other or to shore; distinguished from flags showing nationality, ownership, or organizational status...



"The purpose of the International Code of Signals is to provide ways and means of communication in situations related essentially to safety of navigation and persons, especially when language difficulties arise." It has done this by first establishing a standardized alphabet (the letters A to Z, and the ten digits), along with a spoken form of each letter (to avoiding confusing similar sounding letters, such as 'b', 'p', and 'v'), and associating this alphabet with standardized flags. (See chart, right.)

Combinations of these alphanumeric characters are assigned as codes for various standardized messages. For instance, the master of a ship may wish to communicate with another ship, where his own radio may not be working, or the other ship's call sign is not known, or the other ship may not be maintaining a radio watch. One simply raises the Kilo flag (see diagram at the top), or sends the Morse code equivalent (dash-dot-dash) by flashing light; this has the assigned message of "I wish to communicate with you."

One of the elegant aspects of the ICS is that all of the standardized messages come in nine languages (English, French, Italian, German, Japanese, Spanish, Norwegian, and, since 1969, Russian and Greek). That the sender and receiver(s) are using different languages is immaterial; each language has a book with equivalent messages keyed to the same code. This is also useful in radiotelephony, or even when ships are within hailing distance, if there is no common language: a crewman on a burning ship yells "yuliett alfa vour", and a vessel coming to their aid knows exactly what they need: "material for foam fire extinguishers" (that is, the foaming agent). (See :de:Flaggenalphabet for the German version of single-letter signals.)

The Code also covers procedural aspects (how to initiate a call, the format of a message, how to format date and time, etc.), how naval ships (which usually use their own codes) indicate they are using the ICS (by flying the Code pennant), use in radiotelephony (use of the spoken word "Interco"), and various other matters (such as how an aircraft directs a vessel to another vessel in distress, and how to order unidentified submarines to surface).


Sample Single Letter Messages
Flag Hoist Code Meaning
A I have a diver down; keep well clear at slow speed.
B I am carrying or discharging dangerous goods.
H I have a pilot on board.
Prior to 1969 the Code was much more extensive, covering a wider range of messages, and included a list of five letter codes for every prominent maritime location in the world. Since 1969 it has been reduced to focus on navigation and safety, including a medical section. Signals can be sorted into three groups:
  • Single-letter signals which are very urgent, important, or common.
  • Two-letter signals for other messages, sometimes followed with a numeric "complement" that supplements or modifies the message.
  • Three-letter signals beginning with "M" – these are the Medical Signal Codes.

In some cases additional characters are added to indicate quantities, bearing, course, distance, date, time, latitude, or longitude. There is also provision for spelling words, and for indicating use of other codes. Several of the more common single-letter signals are shown at the right. Two-letter signals cover a broad gamut of situations; the interested reader is urged to download a copy of the Code from the link below.

Repeated characters can be a problem in flaghoist. 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", see diagram below) the Mike, Alfa, and 2nd substitute flags would be flown, the substitute indicating a repeat of the second character.

Medical Signal Code

A hoist of three flags
Flag Hoist Code Meaning

MAA I request urgent medical advice.
The pennant at the bottom indicates a repeat of the second letter.

The Medical Signal Code (incorporated in the International Code of Signals since 1930) is a means of providing assistance when medical personnel are not present. While plain language is preferred in such cases (presumably via radiotelephone), where there are language or communication difficulties the various codes provide a succinct method of communicating to a doctor the nature of the problem, and in return the recommended treatment. Even where there are no language problems the Medical Signal Code is useful in providing a standard method of case description and treatment. There is also a standard list of medicaments (medicines), keyed to a standard ships medicine chest carried by all merchant ships. The Medical signals all begin with the letter "M" (Mike)
followed by two more letters, and sometimes with additional numerals or letters.


The International Code of Signals was proceeded by a variety of naval signals and private signals, most notably Marryat's Code, the most widely used code flags prior to 1857. What is now the International Code of Signals was drafted in 1855 by the British Board of Trade
Board of Trade
The Board of Trade is a committee of the Privy Council of the United Kingdom, originating as a committee of inquiry in the 17th century and evolving gradually into a government department with a diverse range of functions...

 and published by the Board in 1857 as the Commercial Code. It came in two parts: the first containing universal and international signals, and the second British signals only. Eighteen separate signal flags (see chart) were used to make over 70,000 possible messages. Vowels were omitted from the set to avoid spelling out any word that might be objectionable in any language, and some little-used letters were also omitted. It was revised by the Board of Trade in 1887, and was modified at the International Conference of 1889 in Washington, D.C.

During World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 the code was severely tested, and it was found that "when coding signals, word by word, the occasions upon which signaling failed were more numerous than those when the result was successful." The International Radiotelegraph Conference at Washington in 1927 considered proposals for a new revision of the Code, including preparation in seven languages: English, French, Italian, German, Japanese, Spanish and in Norwegian. This new edition was completed in 1930 and was adopted by the International Radiotelegraph Conference held in Madrid in 1932. The Madrid Conference also set up a standing committee for continual revision of the Code. The new version introduced vocabulary for aviation and a complete medical section with the assistance and by the advice of the Office International d’Hygiene Publique. A certain number of signals were also inserted for communications between vessels and shipowners, agents, repair yards, and other maritime stakeholders.

After World War II, The Administrative Radio Conference of the International Telecommunication Union
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...

 suggested in 1947 that the International Code of Signals should fall within the competence of the Inter-Governmental Maritime Consultative Organization (IMCO), which became the IMO. In January 1959, the First Assembly of IMCO decided that the Organization should assume all the functions then being performed by the Standing Committee of the International Code of Signals.

The Second Assembly of IMCO 1961 endorsed plans for a comprehensive review of the International Code of Signals to meet the needs of mariners. The revisions were prepared in the previous seven languages, plus Russian and Greek.

The Code was revised in 1964 taking into account recommendations from the 1960 Conference on Safety of Life at Sea
International Convention for the Safety of Life at Sea
The International Convention for the Safety of Life at Sea is an international maritime safety treaty. The SOLAS Convention in its successive forms is generally regarded as the most important of all international treaties concerning the safety of merchant ships.- History :The first version of the...

 (SOLAS) and the 1959 Administrative Radio Conference. Changes included a shift in focus from general communications to safety of navigation, abandonment of the "vocabulary" method of spelling out messages word by word, adaptation to all forms of communication, and elimination of the separate radiotelegraph and geographical sections; it was adopted in 1965. The 1969 English-language version of the Code (United States edition, revised 2003) is available online through the National Geospatial-Intelligence Agency
National Geospatial-Intelligence Agency
The National Geospatial-Intelligence Agency is an agency of the federal government of the United States with the primary mission of collecting, analyzing and distributing geospatial intelligence in support of national security. NGA was formerly known as the National Imagery and Mapping Agency ...

 (NGA, formerly the National Imagery and Mapping Agency) as Publication 102.

The International Code of Signals is currently maintained by the International Maritime Organization
International Maritime Organization
The International Maritime Organization , formerly known as the Inter-Governmental Maritime Consultative Organization , was established in Geneva in 1948, and came into force ten years later, meeting for the first time in 1959...

, which published a new print edition in 2005.

See also

  • Excerpt from Brown's Signalling (1916), showing earlier versions of ICS flags.
  • Flaghoist signalling
  • List of international common standards
  • Maritime flag signalling
    Maritime flag signalling
    Maritime flag signalling, generally flaghoist signalling, is the principal means other than radio by which ships communicate to each other or to shore; distinguished from flags showing nationality, ownership, or organizational status...

  • Naval flag signalling
    Naval flag signalling
    Naval flag signalling covers various forms of flag signalling, such as semaphore or flaghoist, used by various navies; distinguished from maritime flag signalling by merchant or other non-naval vessels or flags used for identification.-History:...

  • International maritime signal flags
    International maritime signal flags
    The system of international maritime signal flags is one system of flag signals representing individual letters of the alphabet in signals to or from ships...

     (Old version of this article.)
  • Spelling alphabet
    Spelling alphabet
    A spelling alphabet, radio alphabet, or telephone alphabet is a set of words which are used to stand for the letters of an alphabet. Each word in the spelling alphabet typically replaces the name of the letter with which it starts...

  • NATO phonetic alphabet
    NATO phonetic alphabet
    The NATO phonetic alphabet, more accurately known as the NATO spelling alphabet and also called the ICAO phonetic or spelling alphabet, the ITU phonetic alphabet, and the international radiotelephony spelling alphabet, is the most widely used spelling alphabet...

  • Russian Navy Code of Signals
    Russian Navy Code of Signals
    The Russian Navy Code of Signals is a collection of flaghoist signals, which is used together with semaphore alphabet for the transmission of information between the ships of the Russian Navy and also with the shore. Its use resembles that of the signals of other navies but it is only used within...

External links


Sample International Code of Signals Messages
Flag Hoist Code Meaning Flag Hoist Code Meaning Flag Hoist Code Meaning

AC I am abandoning my vessel.
AD I am abandoning my vessel which has suffered a nuclear accident and is a possible source of radiation danger.
AN I need a doctor.

AN 1 I need a doctor; I have severe burns.

AD 2 I need a doctor; I have radiation casualties.
EL Repeat the distress position.

EL 1 What is the position of vessel in distress?
GM I cannot save my vessel.
GN You should take off persons.

GN 1 I wish some persons taken off. Skeleton crew will remain on board.

GN 2 I will take off persons.

GN 3 Can you take off persons?

IT I am on fire.

MAA I request urgent medical advice.

MAB I request you to make rendezvous in position indicated.

MAC I request you to arrange hospital admission.

MAD I am . . . (indicate number) hours from the nearest port.

MS 1 My vessel is a dangerous source of radiation; you may approach from my starboard side.

VG The coverage of low clouds is… (number of octants or eighths of sky covered).

US 4 Nothing can be done until weather moderates.

NC Distress signal
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