International Code Flags or Signaling Flags

Chris Riley by Chris Riley Updated on April 28, 2020. In nauticalknowhow

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International Code Flags or Signaling Flags

Although you may never see them displayed except at fleet parades, around naval installations, and areas with heavy international shipping traffic, International code flags are used to signal between two ships or between ship and shore. Also called signaling flags, they are a set of ship flags of different colors, shapes and markings which used singly or in combination have different meanings. These maritime flags include 26 square flags which depict the letters of the alphabet, ten numeral pendants, one answering pendant, and three substituters or repeaters.

Only a few colors can be readily distinguished at sea. These are: red, blue, yellow, black, and white; and these cannot be mixed indiscriminately. You will notice, for clarity, the flags shown are either red and white, yellow and blue, blue and white, or black and white; besides plain red, white, and blue.

One-flag signals are urgent or very common signals (see meanings below). Two-flag signals are mostly distress and maneuvering signals. Three-flag signals are for points of the compass, relative bearings, standard times, verbs, punctuation, also general code and decode signals. Four-flags are used for geographical signals, names of ships, bearings, etc. Five-flag signals are those relating to time and position. Six-flag signals are used when necessary to indicate north or south or east or west in latitude and longitude signals. Seven-flags are for longitude signals containing more than one hundred degrees.

Nautical Flags: What They Mean And How To Use Them

Some Useful Two Letter Signals:


AC – I am abandoning my vessel. LO – I am not in my correct position: used by a light vessel. RU – Keep clear of me; I am maneuvering with difficulty.
AN – I need a doctor. NC – I am in distress and require immediate assistance. SO – You should stop your vessel instantly.
BR – I require a helicopter. PD – Your navigation lights are not visible. UM – the Harbour is closed to traffic.
CD – I require immediate assistance. PP – Keep well clear of me. UP – Permission to enter Harbour is urgently requested. I have an emergency.
DV – I am drifting. QD – I am going ahead. YU – I am going to communicate with your station by means of the International code of signals.
EF – SOS/MAYDAY has been canceled. QT – I am going astern. ZD1 – Please report me to the Coast Guard, New York
FA – Will you give me my position? QQ – I require health clearance. ZD2 – Please report me to Lloyds, London.
GW – Man overboard. Please take action to pick him up. QU – Anchoring is prohibited. ZL – Your signal has been received but not understood.
JL – You are running the risk of going aground. QX – I request permission to anchor.


Flag Courtesy:


U.S. National Ensign
& Merchant Flag

U.S. Yacht Ensign

It is usually appropriate to fly the U.S. National Ensign (flag) or U.S. Yacht Ensign at the stern of your vessel.

However, when operating internationally, say going to the Bahamas, once in foreign waters you are required to fly the “Q” Flag or “Quarantine Flag” until you have cleared customs. This flag should be hoisted on the starboard spreader. If you are on a power boat with no mast, the “Q” flag can be displayed on the bow.

It is also customary to fly the country’s courtesy flag when operating in the waters of that country. After clearing customs, the “Q” flag should be replaced with the country’s courtesy flag.


When it comes to nautical flags, there are a few dos and don’ts. Naturally, you’ll want to brush up on your sailing flags and what they mean, and where and when to use them. But there are a few other etiquette rules that most books don’t teach you. Here are a few important things about maritime flags:

Don’t fly a foreign courtesy ensign after you have returned to U.S. waters. It may show that you have “been there,” but it is not proper flag etiquette.

Customs regulations and clearance procedures and costs may differ from one foreign country to another. Be sure and check your cruising guide for the proper procedures or try inquiring locally by radio prior to entering a foreign port. Although I have found that most custom officials speak some English or have access to someone who does, don’t forget that you are in their country and you should be prepared to communicate with them in their language.

So, now that you know all about signaling with nautical flags, get them out and wave them high.

About Chris

Outdoors, I’m in my element, especially in the water. I know the importance of being geared up for anything. I do the deep digital dive, researching gear, boats and knowhow and love keeping my readership at the helm of their passions.



  • George on October 2, 2019

    A pink and tan half and half or stripes means any photography is warned and a fine will be issued or worse in some national waters.


  • Ed Zimmerman Jr. USS UNITED STATES Foundation on February 19, 2020

    I thought the signal flag for a quarantined ship was a Black Flag. Someone told me a White Flag with a Black Dot.


    • Dan Reynolds on February 1, 2021

      Publication HO102 is the authoritative reference for international signals and should be adhered to by all mariners. Local deviations cabe found in the appropriate Coast Pilot.


  • Phil Joinville on May 23, 2020

    Are the Watch Hill Yacht Club burgees available for sale?
    What would the cost be?


  • Tim on August 3, 2020

    I came ashore 50 years ago and my memory may be incorrect but I recall a signal on approaching harbour “I have an unusually high death rate among the rats on my ship”

    Am I correct? Can anyone assist? does anyone know the two flag code and the correct wording?

    Many Thanks and Greetings


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