The RF
London Transport AEC Regal IV single-decker
After the war, London Transport’s fleet needed major renewal.  First to be dealt with were the double-deckers, involving the production of nearly 7,000 of the RT family.  Once these were nearing completion, LT turned its attention to the single-deck fleet.  Using ideas from the pre-war Q and underfloor-engined TF classes, the RF used a similar 9.6 litre AEC diesel engine to the RT, but laid on its side under the floor.  The first of 700 was delivered in 1951.
Following the introduction of RFs on Green Line services, the red RFs were delivered in 1952 and 1953.  Initially, the red buses had no doors (or heaters), the absence of doors being a requirement of the Metropolitan Police as it was supposed they would slow down boarding and delay the traffic.  Doors were fitted progressively to the fleet as buses were converted for one-person operation, with the last doorless buses, the last running with conductors, on route 236 in 1971.  At 30 feet, the red buses were built to the then maximum permitted length and carried 41 (later 39) passengers.   
The one-person buses continued in service through the 1970s, outlasting some of their successors, with the last few finishing on Kingston's semi-rural routes in March 1979.