The IMO ship identification number scheme was introduced in 1987. 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.
As Cardiff Queen was laid up in 1966,and Bristol Queen 1967 (approx) would not have had IMO numbers.
