This content was extracted from Wikipedia and is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License
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 As an internationally recognized ship identifier, national official numbers have largely been superseded by the IMO number, though flag states still use national systems, which also cover those vessels not subject to the IMO regulations.