Maritime Mobile Service Identity (MMSI) (MMSI)

A nine-digit identity transmitted by maritime radio systems to identify a ship, coast station, group or other assigned station type.

MMSIs are used by systems including digital selective calling and AIS. Their digit patterns vary by identity type; a ship-station MMSI normally begins with three Maritime Identification Digits identifying the responsible administration, while coast, group, craft-associated and aids-to-navigation identities use other specified formats.

An MMSI is assigned by or under the responsible national administration and must be programmed accurately into compatible equipment. It is an identity rather than proof of a vessel’s current position or operator, and transferring equipment or changing vessel details may require formal amendment rather than simply reusing a number.