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.

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

• each flag spells out a letter of an alphabetic message.
• individual flags have specific and standard meanings; 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".

NATO uses an extra set of flags to communicate specific types of messages.

Letters

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|| I have a diver down; keep well clear at slow speed || I am taking in, or discharging, or carrying dangerous goods. (Originally used by the Royal Navy specifically for military explosives.) || Yes. || Keep clear of me; I am maneuvering with difficulty. || I am altering my course to starboard. || I am disabled; communicate with me. || I require a pilot. When made by fishing vessels operating in proximity on the fishing grounds it means: "I am hauling nets". || I have a pilot on board. || I am altering my course to port. || I am on fire and have dangerous cargo on board: keep well clear of me, for I am leaking dangerous cargo. || I wish to communicate with you. || You should stop your vessel instantly. || My vessel is stopped and making no way through the water. || No. || Man overboard (often attached to the man overboard pole on boats). || The Blue Peter. In harbor — All persons should report on board as the vessel is about to proceed to sea.
At sea — It may be used by fishing vessels to mean: "My nets have come fast upon an obstruction". It may also be used as a sound to mean: "I require a pilot". || My vessel is healthy and I request free pratique. || The way is off my ship; you may feel your way past me. || I am operating astern propulsion. || Keep clear of me; I am engaged in pair trawling. || You are going into danger. || I require assistance. || I require medical assistance. || Stop carrying out your intentions and watch for my signals. || I am dragging my anchor. || I require a tug. When made by fishing vessels operating in close proximity on the fishing grounds it means: "I am shooting nets".

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

Numbers

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|| 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_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

Type of flag	0	1	2	3	4	5	6	7	8	9

Other flags

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|| ICS_Repeat_One.svg || ICS_Repeat_Two.svg || ICS_Repeat_Three.svg || ICS_Repeat_Four.svg

NATO signals

|| ICS_Prepare.svg || ICS_Question.svg || ICS_Negative.svg || ICS_Designation.svg || ICS_Turn.svg || ICS_Screen.svg || ICS_Speed.svg || ICS_Station.svg || ICS_Starboard.svg || ICS_Formation.svg || ICS_Division.svg || ICS_Squadron.svg || ICS_Subdivision.svg || ICS_Emergency.svg

Prompt	First substitute	Second substitute	Third substitute	Fourth substitute
Code/answer	Preparation	Question	Negation	Designation
Alter course	Turn	Screen	Speed	Station
Port	Starboard	Formation	Division	Squadron
Group	Subdivision	Emergency

See also

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• England expects that every man will do his duty
• NATO phonetic alphabet
• Character encoding

External links

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• The flags and their meanings
• Freeware to aid memorizing the flags from The Navy Patuxent Sailing Club
• Flags Fantastic - Nautical flags (A - Z & Pennant)
• La flag-alfabeto - signal flags used for the Esperanto language. Description: the flags for the esperanto letters with diacritical marks have the lighter color in the normal flag replaced with light green, which is not used in any normal flag.
• International Marine Signal Flags
• Signalman manual
• Nautical Flags Alphabet
• brief history of naval signals

Flags | Early telecommunications | Latin alphabet representations

Bannieloù aroueziañ war vor | Námořní vlajková abeceda | Signalflag | Flaggenalphabet | Banderas de señales | Alfabetaj flagoj | Pavillon | Codice Internazionale Nautico | דגלי הקוד הבינלאומי | Seinvlag | 国際信号旗 | Międzynarodowy Kod Sygnałowy | Código internacional de sinais | Сигнальные флаги | Viestiliput