Maritime Mobile Service Identity (MMSI)
A nine-digit number identifying a ship’s radio station, used by AIS and distress systems; distinct from the permanent IMO number.
- Category
- Risk and Sanctions
- Abbreviation
- MMSI
- Last reviewed
How it works
A Maritime Mobile Service Identity (MMSI) is a nine-digit number assigned to a vessel’s radio equipment, used by AIS, digital selective calling and distress alerting. Its leading digits encode the flag state’s maritime identification code.
Unlike the IMO number, which is permanent, an MMSI can change with re-flagging or re-registration. Matching the broadcast MMSI back to a stable IMO identity is a key step in keeping vessel tracking accurate and resistant to manipulation.
Where it shows up on The Maritime
Also known as: MMSI, maritime mobile service identity.
Related terms
Automatic Identification System (AIS)
A VHF transponder system that broadcasts a ship’s identity, position, course and speed for collision avoidance and tracking.
International Maritime Organization (IMO)
The United Nations agency that sets global rules for ship safety, security and pollution prevention.
AIS Spoofing
The falsification of a ship’s broadcast position or identity on AIS to disguise where she really is or what she really is.
More risk and sanctions terms
A plain-English reference definition: our own explanation of a standard shipping concept, not a licensed source or legal advice. See the full glossary or the broader maritime dictionary.
Last reviewed: .