MMSI Validator

MMSI: the 9-digit identity of every vessel on the radio

A Maritime Mobile Service Identity (MMSI) is a nine-digit number that uniquely identifies a maritime radio station — typically a ship, but also coast stations, search-and-rescue aircraft, EPIRB beacons, AIS-SARTs and personal MOB devices. The standard is ITU-R M.585 (Recommendation on assignment and use of identities in the maritime mobile service), maintained by the International Telecommunication Union. Without an MMSI a modern VHF radio with DSC, an AIS transponder or an EPIRB simply cannot operate on the maritime bands.

The 9 digits are not random. The first three are the MID (Maritime Identification Digits), a country code assigned by the ITU. The remaining digits identify the specific station within the country. Decoding the MID is the single most useful trick when reading raw AIS frames: 710xxxxxx through 712xxxxxx are Brazilian, 366xxxxxx and 367xxxxxx are US, 232xxxxxx–235xxxxxx are British.

MMSI format breakdown by station type

• Ship station: MIDxxxxxx — 3-digit MID + 6-digit ship ID. The default form.
• Group ship station: 0MIDxxxxx — leading zero, used for fleet calls.
• Coast station: 00MIDxxxx — two leading zeros, used by VTS centers and Rescue Coordination Centers.
• SAR aircraft: 111MIDxxx — search-and-rescue planes and helicopters.
• EPIRB (Emergency Position-Indicating Radio Beacon): 974xxxxxx — globally allocated, not country-specific.
• AIS-SART (Search and Rescue Transponder): 970xxxxxx — handheld lifeboat beacons.
• MOB device (Man Overboard): 972xxxxxx — personal locator on lifejackets.
• AtoN (Aids to Navigation): 99MIDxxxx — buoys, lights, virtual nav-aids broadcast over AIS.
• Handheld VHF with DSC: 8MIDxxxxx — personal walkie-talkie that does not belong to a single ship.

Reading the MID: country lookup

Common Maritime Identification Digits:

• 710–712 Brazil (issued by ANATEL, coordinated with the Brazilian Navy / Diretoria de Portos e Costas)
• 366, 367, 368, 369 United States; 338 US ship in international waters
• 232, 233, 234, 235 United Kingdom
• 211, 218 Germany; 227 France; 247 Italy; 224, 225 Spain; 244–246 Netherlands; 219, 220 Denmark; 257–259 Norway; 265, 266 Sweden
• 431, 432 Japan; 412, 413, 414 China; 440, 441 South Korea
• 503 Australia; 512 New Zealand; 701 Argentina; 725 Chile; 730 Colombia; 734 Venezuela; 755 Uruguay

MMSI vs IMO number: two IDs that confuse new sailors

A ship has two unrelated international identifiers and people mix them up constantly. The IMO number is a 7-digit permanent hull ID issued by the International Maritime Organization (via IHS Markit) when the keel is laid; it never changes during the life of the ship, even if the ship is sold and reflagged. The MMSI is tied to radio licensing in a specific flag state, so it does change when a ship is sold and re-registered under a new flag — the new flag state's telecom regulator (ANATEL in Brazil, FCC in the US, Ofcom in the UK) issues a new MMSI with its own MID. AIS broadcasts include both, so historical fleet trackers key on IMO for the long term and MMSI for current radio sessions.

Where MMSI shows up: AIS, DSC, EPIRB and GMDSS

• AIS (Automatic Identification System): every position report on VHF channels 87B/88B (161.975 / 162.025 MHz) includes the MMSI plus position, course over ground, speed over ground, heading and navigational status. AIS Class A is mandatory on SOLAS-class ships; Class B is common on yachts and fishing vessels.
• DSC (Digital Selective Calling): the digital channel on VHF Ch 70 used to ring a specific ship by MMSI before voice, like a phone call. Distress alerts use Ch 70.
• EPIRB / PLB: 406 MHz emergency beacons relay a 15-character hex ID that decodes to country + MMSI (or serial), routed via COSPAS-SARSAT satellites to the nearest RCC.
• GMDSS (Global Maritime Distress and Safety System): the umbrella regulatory framework, mandatory on ocean-going commercial vessels, that prescribes DSC + AIS + EPIRB + SART, all keyed by MMSI.

Allocation in Brazil: ANATEL and the Marinha

In Brazil MMSI assignment is a joint process. The radio license is issued by ANATEL, the federal telecoms regulator, while ship registration and the TIE (Título de Inscrição da Embarcação) is run by the Marinha do Brasil through the Diretoria de Portos e Costas (DPC). Vessel owners apply for the radio license (Licença de Funcionamento de Estação Móvel Marítima), receive an MMSI in the 710–712 range and program it once into the radio or AIS transponder. The MMSI is non-rewritable on most consumer units: re-entering it after installation usually requires a service authorization or returning the unit to the manufacturer.

Tracking and lookup tools

• MarineTraffic, VesselFinder, ShipFinder, FleetMon: web/mobile AIS aggregators that search by MMSI, IMO or name.
• AIS-receivers (dAISy, RTL-SDR with rtl-ais, Class B transponders): decode raw NMEA AIVDM sentences locally.
• ITU MARS (Maritime mobile Access and Retrieval System): official ITU database of issued MMSIs, free with registration.
• Brazilian CDA (Cadastro de Embarcações): marine registry maintained by the DPC.

FAQ

Does my MMSI change? Only if you change flag state (reflag). Selling the boat domestically without changing the flag keeps the MMSI; selling internationally invalidates it and the new owner applies for a new one under the new flag's MID.

What's the difference between MMSI and IMO number? IMO is a permanent 7-digit hull ID for the life of the ship; MMSI is a 9-digit radio ID tied to the current flag state and changes on reflag.

Does a small recreational vessel need an MMSI? Yes, if it carries any DSC-capable VHF radio or AIS transponder. Without an MMSI the radio's distress button cannot send a digital alert — voice-only on Ch 16 still works, but you lose the GMDSS one-touch alarm with position.

How do I read which country a MMSI belongs to? Take the first three digits and look them up in the ITU MID table. 710–712 is Brazil, 366–369 is US, 232–235 is UK.

What about EPIRB beacons starting with 974? Those are globally allocated EPIRB identities, not tied to a country MID — the country is encoded elsewhere in the 15-hex beacon ID transmitted to COSPAS-SARSAT.