Each GMDSS ship station is allocated its own unique nine digit MMSI number which is included automatically in each DSC call made by the station.

Included in the MMSI number are the maritime identification digits (MID) which identify the country licencing/controlling the station.

Three types of MMSI numbers are in common use to identify individual ships, groups of ships and coast stations.
The following are examples using the MID 232 (United Kingdom):

  1. Ship station 232001021
  2. Group of stations 023201143
  3. Coast station 002320018