What is a MMSI?
The Maritime Mobile Service Identity is a unique nine digit number that identifies transmitted signals within the GMDSS system. It functions like a telephone number for the devices on your boat.
The MMSI is assigned to a vessel, and the same MMSI is programmed into all shipboard equipment that transmits and receives digital signals, including VHF radio, medium and high frequency radios, AIS (Automatic Identification System), and INMARSAT satellite teminals. There is an important exception: the EPIRB (Emergency Position Indicating Radio Beacon), which must be registered separately from this site through the NOAA web site.
MMSIs consist of a three digit country code (called a MID) and a six digit station code. The United States MID codes are 366, 367, 368, 379, 559, 303, 338, and 358.
MMSIs available through USPS are for use by non-compulsory (voluntary) vessels that boat within US domestic waters only.
It is illegal for you to self-assign a MMSI. Use of an unauthorized identity can seriously compromise search and rescue efforts, including misdirection of SAR forces and alerting of the wrong emergency contacts.