Radio ID
What Is an MMSI Number? How to Get One for Your Boat
Published · Last checked October 2026
An MMSI (Maritime Mobile Service Identity) is a nine-digit number that identifies a vessel or radio station in digital communications. It is programmed into DSC VHF radios and AIS transponders, so a distress alert or AIS signal tells rescuers exactly who you are. In the UK you get one free from Ofcom when you apply for a Ship Radio Licence. Vessel MMSIs start with a three-digit country code: 232, 233, 234 or 235 for the UK.
How the number is built
The first digits tell you what kind of station it is. The Maritime Identification Digits (MID) identify the country.
| Format | Meaning | Example |
|---|---|---|
| MIDxxxxxx | Individual ship | 235012345 (UK yacht) |
| 0MIDxxxxx | Group of ships | 023212345 |
| 00MIDxxxx | Coast station (e.g. coastguard) | 002320011 |
| 970xxxxxx | AIS search and rescue transmitter | AIS-SART |
| 972xxxxxx | AIS man overboard device | Personal AIS beacon |
So if your radio shows an incoming call from a number beginning 00232, it is a UK coast station.
How to get an MMSI in the UK
- Apply for a Ship Radio Licence on the Ofcom website. It is free online and lasts for life, though you must keep details up to date.
- List the equipment aboard: fixed VHF with DSC, AIS, EPIRB and so on.
- Ofcom issues the licence with your call sign and MMSI.
- Program the MMSI into the radio. Many sets only let you enter it once, so check it carefully; a dealer can reset it if you make a mistake.
A handheld DSC radio used on more than one boat needs a Ship Portable Radio Licence and gets its own MMSI, separate from the boat's.
Where the MMSI is used
- DSC VHF: identifies you in every distress, urgency and routine call.
- AIS: broadcast with your position, so other ships see your name and MMSI.
- EPIRB: some beacons are coded with the MMSI, and the beacon registration links to your details.
- Mayday calls: give the MMSI by voice as part of the identification.
Read more in what is DSC and the VHF DSC lesson.