DSC uses MMSI to enable automated distress calls via which system on marine radios?

• A. MMSI
• B. GPS coordinates
• C. VHF channel number
• D. AIS transponder data

Answer: (A)

MMSI is the identifier that makes DSC distress calls automatic. Digital Selective Calling uses a vessel’s Maritime Mobile Service Identity to address a distress alert so the message can be directed to the right receiver—coast guard, rescue coordination centers, or other ships—without needing manual dialing. The MMSI uniquely identifies the sender, enabling rapid, automated alerting and response.

GPS coordinates may be included as part of the distress data if the radio is connected to a position source, but they are data payload, not the addressing mechanism. Other items like a VHF channel number or AIS data serve different roles and don’t provide the vessel’s unique identity for routing the distress alert.