The line was a branch of the Metropolitan line until 1988, though in later years it was increasingly operated as a separate line, with the sections not used by the rest of the Metropolitan line (from Hammersmith to Baker Street and from Liverpool Street to Barking) not included on the main Metropolitan line maps. This is also reflected in the line's use of London Underground C69 Stock equipment, as opposed to the London Underground A60 Stock used on the 'main' Metropolitan Line.