Group call MMSI (0MIDxxxxx)

What it identifies

A single leading zero (followed by a non-zero digit) is a group MMSI: an address used to call a set of stations at once — a company fleet, a convoy, a class of vessels — over digital selective calling (DSC).

How to read it

Group identities are call addresses, not transmitters, so they should not appear as positions on a plot. If one does, the transponder has been programmed with a group number by mistake.

Does it give a flag?

Not a flag — the MID in digits 2 to 4 identifies the administration, not a ship’s registry.

Every vessel page on this site works this out before printing a flag. Where the MMSI is not a ship station, the page names the kind of station instead — a wrong flag is worse than an honest “this is a coast station”.

All MMSI formats

Have a number to check? The MMSI decoder applies these rules to any nine digits. For the background, read Reading an MMSI.