MMSI Number

The Maritime Mobile Service Identity is a nine-digit number used to identify a ship's radio station in the GMDSS (Global Maritime Distress and Safety System). It is programmed into the vessel's DSC (Digital Selective Calling) VHF, MF, and HF radio equipment, as well as AIS transponders and EPIRBs, enabling authorities and other vessels to identify the source of a distress call or safety message. MMSI numbers are assigned by the national telecommunications authority of the flag state. For a radio operator or GMDSS-trained officer, the MMSI is the digital address of the vessel. When a distress alert is transmitted via DSC, the receiving coast radio station or vessel automatically identifies the calling ship by its MMSI and can retrieve registration details from the database. This is why correct registration of the MMSI with accurate ship details — name, call sign, length, and emergency contact — is operationally critical for SAR response. MMSIs are also programmed into EPIRBs and SARTs. A vessel that has changed ownership or flag without updating its MMSI registration creates a dangerous gap: responders to a distress call may contact the wrong company or, worse, find that the MMSI is unregistered. SOLAS requires that radio equipment be maintained and certified, and that the MMSI be correctly registered with the national authority. Officers should verify MMSI registration as part of the vessel's pre-voyage checks.