🔍 Key Concepts

• Maritime Mobile Service Identity (MMSI) structure and purpose • How Maritime Identification Digits (MID) are used in radio and AIS numbers • Relationship between MID and a ship’s flag state / country

💭 Think About

• When you see the term MID in the context of MMSI or AIS, what part of the vessel’s identity is being encoded by those first few digits? • Which of the options (port, nationality, tonnage, vessel type) is normally indicated by a short numeric code that stays the same for all ships from a given country? • Think about radio call numbers or phone country codes: what do their leading digits usually represent, and which answer choice is most similar to that idea?

✅ Before You Answer

• Verify what the first three digits of an MMSI number represent in ITU and GMDSS documentation. • Ask yourself: does port of registry change within a country while this code stays fixed, or is the code tied to something more general? • Confirm whether gross tonnage or passenger status is typically shown in any short numeric prefix like MID, or if those are recorded elsewhere (certificates, Safe Manning, etc.).