Maritime identification digits are used by radio communication facilities to identify their home country or base area in Digital Selective Calling (DSC), Automatic Transmitter Identification System (ATIS), and Automatic Identification System (AIS) messages as part of their Maritime Mobile Service Identities.
In the United States (one of whose MIDs is 366), federal MMSIs are assigned by the National Telecommunications and Information Administration, and are normally (but not always) formed as 3669xxxxx.
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