International maritime signal flags refers to various flags used to communicate with ships, yachts and people on or near the sea.
The principal system of flags and associated codes is the International Code of Signals.
Various navies have flag systems with additional flags and codes, and other flags are used in special uses, or have historical significance.
- There are various methods by which the flags can be used as signals
- Each flag spells an alphabetic message, letter by letter
- One or more flags form a code word whose meaning can be looked up in a code book held by both parties
- In yacht racing and dinghy racing, flags have other meanings
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 and their meaning
|“I have a diver down; keep well clear at slow speed.”|
|“I am taking in or discharging or carrying dangerous goods.”|
|“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.”
By fishing vessels near fishing grounds: “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.”|
|“I wish to communicate with you.”|
|In harbour: “The ship is quarantined.”
At sea: “You should stop your vessel instantly.”
|“My vessel is stopped and making no way through the water.”|
|“Man overboard.”[b] (often attached to the man overboard pole on boats).|
In harbour: 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.”
|“My vessel is ‘healthy’ and I request free pratique.”|
|(No ICS meaning as single flag)|
|“I am operating astern propulsion.”|
|Fishing boats: “Keep clear of me; I am engaged in pair trawling.”|
|“You are running 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.”
By fishing vessels near fishing grounds: “I am shooting nets.”[d]
- Note – N and C together (“no” and “yes”) is used as a distress signal.
|Number||NATO flag||International flag|
Substitute or repeater flags allow messages with duplicate characters to be signaled without the need for multiple sets of flags. IE the second substitute flag repeats the second flag in the hoist or signal.
The substitute flags are as follows:
|First substitute||Second substitute||Third substitute||Fourth substitute|
Examples of multiple-flag signals