The Regal IV was a familiar sight on the streets of London in post-war Britain for three decades. The Regal IV was built between 1951 and 1953 by the Associated Equipment Company. The design of the RF used a high-floor single deck, with seating for up to 41 passengers. Unlike modern rear-engined buses, the 9.6 litre engine on the RF was mounted centrally, laid on it side, beneath the floor. This, combined with a square front maximised space for the driver and passengers. The RF proved a very effective design and remained in service for nearly thirty years. The Regal IV stands out alongside the more famouse AEC Routemaster double-dekcer bus as one the most iconic single-decker buses of post-war Britain.
The Regal IV was developed to replace the old single-deck buses of London's post-war bus fleet. The chassis design was by Associated Equipment Company (AEC). A prototype, registered UMP 227 was developed in 1949, with Park Royal Vehicles (PRV) vehicle.
The 700 examples built for London Transport (LT) - designated the RF - were fitted with Metro-Cammell bodywork, designed by Douglas Scott. Used across London, LT's Green Line Coaches, connecting London with the Home Counties, used the RF from 1951 before the RF entered service, in the centre of London by 1952.
Finally, the RF entered service with London General Country Services in 1953. The flexibility of the RF, and the longevity of its Metro-Cammell coachwork allowed the bus to remain in service throughout the 1960s and 1970s, with the last RF withdrawn from service in March 1979. The Regal IV appeared in different guises, with bodies by coach-builders, including Eastern Coach Works and PRV.
Preserved examples of the RF can be seen at transport rallies across the country, proving the durability of the RF's design.