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The set of signal flags on the bridge of the Liberty ship SS Jeremiah O'Brien

The system of international maritime signal flags is a way of representing individual letters of the alphabet in signals to or from ships. It is a component of the International Code of Signals (INTERCO).[1]

There are various methods that the flags can be used as signals:

  • each flag spells out an alphabetic message, letter by letter.
  • individual flags have specific and standard meanings[2]; for example, diving support vessels raise the "A flag" indicating their inability to move from their current location because they have a diver underwater.
  • one or more flags form a code word whose meaning can be looked up in a code book held by both parties. An example is the Popham numeric code used at the Battle of Trafalgar.
  • in yacht racing and dinghy racing, flags have other meanings; for example, the P flag is used as the "preparatory" flag to indicate an imminent start, and the S flag means "shortened course" (for more details see Race Signals).

NATO uses the same flags, with a few unique to warships, alone or in short sets to communicate various unclassified messages. The NATO usage generally differs from the International meanings, and therefore warships will fly the Code/Answer flag above the signal to indicate it should be read using the International meaning.


Letter flags (with ICS meaning)

* ^  N and C together (No and Yes) is used as a distress signal.

** Also signallable on a ship's whistle using Morse code. See International Code of Signals.


Number: 0 1 2 3 4 5 6 7 8 9
NATO flags ICS Zero.svg ICS One.svg ICS Two.svg ICS Three.svg ICS Four.svg ICS Five.svg ICS Six.svg ICS Seven.svg ICS Eight.svg ICS Niner.svg
ICS ICS Pennant Zero.svg ICS Pennant One.svg ICS Pennant Two.svg ICS Pennant Three.svg ICS Pennant Four.svg ICS Pennant Five.svg ICS Pennant Six.svg ICS Pennant Seven.svg ICS Pennant Eight.svg ICS Pennant Niner.svg

Other flags

ICS Repeat One.svg ICS Repeat Two.svg ICS Repeat Three.svg ICS Repeat Four.svg
First substitute Second substitute Third substitute Fourth substitute

Allied signals

ICS Answer.svg ICS Prepare.svg ICS Question.svg ICS Negative.svg ICS Designation.svg
Code/answer (ANS) Preparative (PREP) Question (INT) Negation (NEGAT) Designation (DESIG)
ICS Corpen.svg ICS Turn.svg ICS Screen.svg ICS Speed.svg ICS Station.svg
Course Pennant (CORPEN) Turn (TURN) Screen (SCREEN) Speed (SPEED) Station (STATION)
ICS Port.svg ICS Starboard.svg ICS Formation.svg ICS Division.svg ICS Squadron.svg
Port (PORT) Starboard (STBD) Formation (FORM) Division (DIV) Squadron (SQUAD)
ICS Group.svg ICS Subdivision.svg ICS Emergency.svg
Group (FLOT) Subdivision (SUBDIV) Emergency (EMERG)

See also


International Code of Signals. International Maritime Organisation. 1995.  

  1. ^ International Marine Signal Flags
  2. ^ AB Nordbok. "The Lore of Ships", page 138. New York: Crescent Books, 1975.

External links


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