ⓘ Official number

                                     

ⓘ Official number

Official numbers are ship identifier numbers assigned to merchant ships by their country of registration. Each country developed its own official numbering system, some on a national and some on a port-by-port basis, and the formats have sometimes changed over time. As an internationally recognized ship identifier, national official numbers have been superseded by the IMO ship identification number, though flag states still use national systems, which also cover those vessels not subject to the IMO regulations.