COLREGs Annex IV: Distress signals under Annex IV
Last reviewed: October 14, 2026
Annex IV lists signals that indicate distress and need of assistance. They may be used or exhibited together or separately. The International text prohibits using these signals for any other purpose, and prohibits other signals that may be confused with them. The Inland text adds a high intensity white light signal.
What it says
The listed signals, used or exhibited together or separately, indicate distress and need of assistance.
“The following signals, used or exhibited either together or separately, indicate distress”
A gun or other explosive signal fired at intervals of about a minute is a distress signal.
COLREGs Annex IV(a)“A gun or other explosive signal fired at intervals of about a minute;”
A signal sent by radiotelephony consisting of the spoken word "Mayday" is a distress signal.
COLREGs Annex IV(e)“A signal sent by radiotelephony consisting of the spoken word “Mayday”;”
A distress alert by digital selective calling (DSC) transmitted on VHF channel 70 is a distress signal.
COLREGs Annex IV(l)“A distress alert by means of digital selective calling (DSC) transmitted on:”
Signals transmitted by emergency position-indicating radio beacons are distress signals.
COLREGs Annex IV(n)“Signals transmitted by emergency position-indicating radio beacons;”
Inland: A high intensity white light flashing at regular intervals from 50 to 70 times per minute is a distress signal.
COLREGs Annex IV(p)“A high intensity white light flashing at regular intervals from 50 to 70 times per”
International: Using or exhibiting any of these signals for any purpose other than indicating distress and need of assistance is prohibited. Using other signals that may be confused with them is also prohibited.
COLREGs Annex IV 2“The use or exhibition of any of the foregoing signals except for the purpose of indicating distress and need of assistance and the use of other signals which may be confused with any of the above signals is prohibited.”
Common questions
What radio word signals distress under Annex IV?
A signal sent by radiotelephony consisting of the spoken word "Mayday" indicates distress and need of assistance.
“A signal sent by radiotelephony consisting of the spoken word “Mayday”;”
How often is a distress gun signal fired?
A gun or other explosive signal is fired at intervals of about a minute.
“A gun or other explosive signal fired at intervals of about a minute;”
Can I use a distress signal for other purposes?
No. International: using or exhibiting these signals for any purpose other than indicating distress and need of assistance is prohibited, as is using signals that may be confused with them.
“The use or exhibition of any of the foregoing signals except for the purpose of indicating distress and need of assistance and the use of other signals which may be confused with any of the above signals is prohibited.”
Is a flashing white light a distress signal on inland waters?
Inland: yes. A high intensity white light flashing at regular intervals from 50 to 70 times per minute is listed as a distress signal.
“A high intensity white light flashing at regular intervals from 50 to 70 times per”
The text of COLREGs Annex IV
U.S. Coast Guard, Navigation Rules and Regulations Handbook
1. The following signals, used or exhibited either together or separately, indicate
International (COLREGs)
distress and need of assistance:
(a) a gun or other explosive signal fired at intervals of about a minute;
(b) a continuous sounding with any fog-signaling apparatus;
(c) rockets or shells, throwing red stars fired one at a time at short intervals;
(d) a signal made by any signaling method consisting of the group. . . – – – . . .
(SOS) in the Morse Code;
(e) a signal sent by radiotelephony consisting of the spoken word “Mayday”;
(f) the International Code Signal of distress indicated by N.C.;
(g) a signal consisting of a square flag having above or below it a ball or anything resembling a ball;
(h) flames on the vessel (as from a burning tar barrel, oil barrel, etc.);
(i) a rocket parachute flare or a hand flare showing a red light;
(j) a smoke signal giving off orange-colored smoke;
(k) slowly and repeatedly raising and lowering arms outstretched to each side;
(l) a distress alert by means of digital selective calling (DSC) transmitted on:
(i) VHF channel 70, or
(ii) MF/HF on the frequencies 2187.5 kHz ‡, 8414.5 kHz, 4207.5 kHz, 6312 kHz, 12577 kHz or 16804.5 kHz;
(m) a ship-to-shore distress alert transmitted by the ship’s Inmarsat or other mobile satellite service provider ship earth station;
(n) signals transmitted by emergency position-indicating radio beacons;
(o) approved signals transmitted by radiocommunication systems, including survival craft radar transponders. 2. The use or exhibition of any of the foregoing signals except for the purpose of indicating distress and need of assistance and the use of other signals which may be confused with any of the above signals is prohibited. 3. Attention is drawn to the relevant sections of the International Code of Signals, the International Aeronautical and Maritime Search and Rescue Manual, Volume III, and the following signals:
(a) a piece of orange-colored canvas with either a black square and circle or other appropriate symbol (for identification from the air);
(b) a dye marker. ‡ The U.S. Coast Guard terminated monitoring DSC safety and distress frequency 2187.5 kHz on August 1, 2013. (78 FR 42102).
Inland Rules
The following signals, used or exhibited either together or separately, indicate distress and need of assistance:
(a) A gun or other explosive signal fired at intervals of about a minute;
(b) A continuous sounding with any fog-signaling apparatus;
(c) Rockets or shells, throwing red stars fired one at a time at short intervals;
(d) A signal made by any method consisting of the group . . . – – – . . . (SOS) in the Morse Code;
(e) A signal sent by radiotelephony consisting of the spoken word “Mayday”;
(f) The International Code Signal of distress indicated by N.C.;
(g) A signal consisting of a square flag having above or below it a ball or anything resembling a ball;
(h) Flames on the vessel (as from a burning tar barrel, oil barrel, etc.);
(i) A rocket parachute flare or a hand flare showing a red light;
(j) A smoke signal giving off orange-colored smoke;
(k) Slowly and repeatedly raising and lowering arms outstretched to each side;
(l) A distress alert by means of digital selective calling (DSC) transmitted on:
(i) VHF channel 70, or
(ii) MF/HF on the frequencies 2187.5 kHz ‡, 8414.5 kHz, 4207.5 kHz, 6312 kHz, 12577 kHz or 16804.5 kHz;
(m) A ship-to-shore distress alert transmitted by the ship’s Inmarsat or other mobile satellite service provider ship earth station;
(n) Signals transmitted by emergency position-indicating radio beacons;
(o) Signals transmitted by radiocommunication systems, including survival craft radar transponders meeting the requirements of 47 CFR 80.109; and
(p) A high intensity white light flashing at regular intervals from 50 to 70 times per minute. for the purpose of indicating distress and need of assistance and the use of other signals which may be confused with any of the above signals is prohibited. International Code of Signals, the International Aeronautical and Maritime Search and Rescue Manual, Volume III, the International Telecommunication Union Radio Regulations, and the following signals:
(a) A piece of orange-colored canvas with either a black square and circle or other appropriate symbol (for identification from the air);
(b) A dye marker. ‡ The U.S. Coast Guard terminated monitoring DSC safety and distress frequency 2187.5 kHz on August 1, 2013. (78 FR 42102).
Sections it refers to
The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of August 12, 2024. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.