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MMSI
An MMSI (Maritime Mobile Service Identity) is a unique nine-digit number that identifies a vessel's radio equipment. It is used by DSC radios and AIS transponders, and is issued with the vessel's radio licence.
What is an MMSI used for?
The MMSI is transmitted automatically when a vessel sends a digital selective calling (DSC) distress alert and is broadcast continuously by its AIS transponder, so rescue services and other vessels can identify who is calling. The first three digits are the Maritime Identification Digits, which show the country that issued the number.
Does an MMSI expire?
The number itself stays with the vessel, but the ship radio licence it belongs to is issued by the flag state’s radio authority and may need renewing or updating when the vessel changes owner, flag or equipment. This is why the radio licence belongs in the vessel’s document register with an expiry date.
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