IALACOLREG
Academy

COLREG

Rule 37: Distress Signals

If your vessel is in distress and requires assistance, COLREG says you must use or exhibit the signals described in Annex IV.

Rule 37 of 41

Decide

Decision 1 of 2

You hear this continuous sound from a fog-signalling apparatus. What does it mean?

The rule in plain words

  1. When does it apply?When a vessel is in distress and requires assistance. Then she shall use or exhibit the signals described in Annex IV.
  2. Where do you find the signals?In Annex IV to COLREG. Rule 37 points there for the signals it describes.
  3. Can they serve any message?No. The rule links them to distress requiring assistance; they are not free-use signals.
Recognised distress signals include a square flag with a ball above or below, red hand flares and orange smoke. They indicate distress and the need for assistance.
1 of 2

Before you read on: what would you do?

Question 1/1

What situation activates Rule 37?

Listen to it

Play each signal and listen: this is how it sounds at sea.

Frequent mistakes

  • Wrong: "Any urgent message allows a vessel to use Annex IV signals."

    Right: Rule 37 ties them to a vessel in distress that requires assistance.

  • Wrong: "Rule 37 lists every signal."

    Right: It refers you to Annex IV, where the signals are described.

  • Wrong: "You must choose between using and exhibiting."

    Right: The rule allows either action: use or exhibit the described signals.

Exam keys & interpretation

  1. If "requires assistance" becomes "wants to warn", the option no longer states Rule 37's condition.
  2. "Use or exhibit" gives two valid actions; do not confuse them with choosing a signal outside Annex IV.
  3. If asked where the signals are described, answer "Annex IV".

How to read it

Read the rule in two steps: check distress and required assistance; then consult the signals in Annex IV.

"Shall use or exhibit" makes those signals the regulated response for that situation, not a free repertoire.

Key points

  • Rule 37 = signals for a vessel in distress.
  • Two-part condition: distress + assistance required.
  • Action: use or exhibit.
  • Reference: Annex IV to COLREG.

Test your knowledge

3 questions to check it. Pick an answer to see why.

Question 1/3

Where are the Rule 37 signals described?

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Official text

IMO COLREG 1972 U.S. Coast Guard — International Navigation Rules (2024)

Full wording of the rule, reproduced from the official source below.

When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annex IV to these Regulations.
Source:

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More resources

Reviewed by Ramon Curto, Nautical teacher at IECNPC · Last reviewed:

Frequently asked questions about COLREG Rule 37

What are the COLREG distress signals?

Rule 37 requires a vessel in distress and requiring assistance to use the signals in Annex IV: red rocket, parachute or hand flares, orange smoke, SOS, the spoken word MAYDAY, the code signal NC, flames on the vessel, a continuous sounding with any fog-signalling apparatus, and DSC, satellite or EPIRB alerts.

Is MAYDAY a COLREG distress signal?

Yes. The spoken word MAYDAY by radiotelephony is one of the Annex IV signals listed under Rule 37, alongside SOS by any signalling method and the International Code Signal of distress NC.

When may a distress signal be used?

Only when a vessel is in distress and genuinely requires assistance (Rule 37). Using a distress signal for urgency or routine communications is a common mistake.