Rule 37 & Annex IV · Distress
SOS / Mayday (distress)
The Morse group · · · — — — · · · (SOS) by any signalling method, or the spoken word “Mayday” by radiotelephone — Annex IV distress signals.
You hear: 3 short blasts, then 3 prolonged blasts, then 3 short blasts.
Meaning
Annex IV includes “a signal made by any signalling method consisting of the group · · · — — — · · · (SOS) in the Morse Code” and “a signal sent by radiotelephony consisting of the spoken word ‘Mayday’.” SOS can be sent by whistle, light, or any other method — three shorts, three longs, three shorts.
Key facts
- Sounded by
- Vessel in distress, by any signalling method
- Repeated
- Not a repeating signal — sounded when the situation calls for it
- Applies under
- International & US Inland
- Notation
- · · · — — — · · ·
Related signals
Source: Rule 37 & Annex IV — USCG Navigation Rules (International & Inland)
Rule text is reproduced from the public-domain USCG Navigation Rules. Audio is synthesized to Rule 32 timings.