A quick look at online particulars of the future HMCS William Hall having the United Nations International Maritime Organization (IMO) number 4702539 shows Canada’s six Arctic and offshore patrol ship fleet are not considered warships.

IHS Maritime Explains Why:


(Circular letter No.1886/Rev.5)

The IMO ship identification number scheme was introduced in 1987 through adoption of resolution A.600(15), as a measure aimed at enhancing “maritime safety, and pollution prevention and to facilitate the prevention of maritime fraud”. It aimed at assigning a permanent number to each ship for identification purposes. That number would remain unchanged upon transfer of the ship to other flag(s) and would be inserted in the ship’s certificates. When made mandatory, through SOLAS regulation XI/3 (adopted in 1994), specific criteria of passenger ships of 100 gross tonnage and upwards and all cargo ships of 300 gross tonnage and upwards were agreed.    

The implementation of the scheme became mandatory as of 1 January 1996. In 2013, IMO adopted resolution A.1078(28) in order to allow the voluntary application of the IMO Ship Identification Number Scheme to fishing vessels of 100 gross tons and above.

SOLAS regulation XI-1/3 requires ships’ identification numbers to be permanently marked in a visible place either on the ship’s hull or superstructure. Passenger ships should carry the marking on a horizontal surface visible from the air. Ships should also be marked with their ID numbers internally.   

The IMO ship identification number is made of the three letters “IMO” followed by the seven-digit number assigned to all ships by IHS Maritime (formerly known as Lloyd’s Register-Fairplay) when constructed. This is a unique seven digit number that is assigned to propelled, sea-going merchant ships of 100 GT and above upon keel laying with the exception of the following:

·        Ships without mechanical means of propulsion

·        Pleasure yachts

·        Ships engaged on special service (e.g. lightships, SAR vessels)

·        Hydrofoils, air cushion vehicles

·        Floating docks and structures classified in a similar manner

·        Ships of war and troopships


This number is assigned to the total portion of the hull enclosing the machinery space and is the determining factor, should additional sections be added.

The IMO number is never reassigned to another ship and is shown on the ship’s certificates.


IMO ship identification number – contact

IHS Maritime is the manager of the scheme and, as such, identifies and assigns IMO numbers without charge.


For verification of IMO numbers for individual ships, IHS Maritime operates a service following receipt of a completed IMO number Request Form.


By Editor