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Distress signals at sea: COLREGS Annex IV

Annex IV of the collision regulations lists the signals that mean a vessel is in distress and needs assistance. Any of them can be used on its own or together with others. Here they all are, grouped so they're easier to remember.

Sound

  • A gun or other explosive signal fired at intervals of about a minute. (Annex IV 1a)
  • A continuous sounding with any fog-signalling apparatus. (Annex IV 1b)

Flares, smoke and flames

  • Rockets or shells throwing red stars, fired one at a time at short intervals. (Annex IV 1c)
  • A rocket parachute flare or a hand flare showing a red light. (Annex IV 1i)
  • A smoke signal giving off orange-coloured smoke. (Annex IV 1j)
  • Flames on the vessel, as from a burning tar barrel or oil barrel. (Annex IV 1h)

Flags, shapes and signalling

  • SOS (· · · — — — · · ·) in Morse code, by any signalling method. (Annex IV 1d)
  • The International Code signal of distress, the flags N over C. (Annex IV 1f)
  • A square flag with a ball, or anything resembling a ball, above or below it. (Annex IV 1g)
  • Slowly and repeatedly raising and lowering arms outstretched to each side. (Annex IV 1k)

Radio and electronic

  • The spoken word “Mayday” by radiotelephony. (Annex IV 1e)
  • A digital selective calling (DSC) distress alert on VHF channel 70, or on the MF/HF DSC distress frequencies. (Annex IV 1l)
  • A ship-to-shore distress alert from the vessel's Inmarsat or other mobile satellite service ship earth station. (Annex IV 1m)
  • Signals transmitted by emergency position-indicating radio beacons (EPIRBs). (Annex IV 1n)
  • Approved signals transmitted by radiocommunication systems. (Annex IV 1o)

For being seen from the air

Annex IV also draws attention to two signals that help aircraft find you:

  • a piece of orange-coloured canvas with a black square and circle, or another appropriate symbol;
  • a dye marker in the water.

Misuse is prohibited

Using any of these signals except to indicate distress and need of assistance is prohibited, and so is using any other signal that could be confused with them. Out-of-date flares need proper disposal, not a bonfire-night display.

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Questions

What are the international distress signals at sea?

They're listed in Annex IV of the COLREGS. They include a Mayday by radio, a DSC distress alert, red flares, orange smoke, SOS in Morse, the code flags NC, a continuous fog signal, and slowly raising and lowering outstretched arms.

What colour are distress flares?

Red, whether a rocket parachute flare or a hand flare. Orange is used for daytime distress smoke signals.

Can I use a distress signal if I'm not in distress?

No. Annex IV prohibits using any of the distress signals except to indicate distress and need of assistance, and also prohibits other signals that could be confused with them.

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Last checked 4 November 2026. DeckPrep is an independent revision tool and is not affiliated with, endorsed by, or operated by the RYA. Always check current requirements with the RYA.