Official numbers and other numerical identifiers

(new 23 October 1906)

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Official numbers

Official numbers are the equivalent for ships of modern motor vehicle registration numbers and engine numbers or personal Inland Revenue or Social Security numbers. They should be unique to a particular ship. A ship should never hold two under the same national jurisdiction although they will invariably change if the ship transfers to another jurisdiction.

The British Empire introduced them in 1855, the United States in 1867 and Japan and Sweden in the 1880’s.

Probably at least half the world’s merchant ships from the mid 19^th century through to the 1960’s had an official number under one or more of these jurisdictions. They therefore have considerable utility for data identification even though the ships of many important countries never had them.

LR/IMO numbers

Lloyd’s Register allocated its own standard numerical identifiers for merchant ships of 100 tons and over world-wide during the late 1960’s, initially in a 6-digit format. They appear in their present 7 digit format in Lloyd’s Register for 1969 and thereafter and were originally termed “LR numbers”.

These have been formally adopted by the International Maritime Organisation and function as “world official numbers” for ship identification and tracking purposes, hence the acronym LR/IMO. They are generally painted conspicuously on the hull of modern ships to which IMO regulations apply (the majority of merchant ships above a low size threshold but excluding some types).