The Associated Engineering Company and the engineering department of London Transport collaborated for 3 years before World War II on a new model of the Regent chassis known as the Regent RT Type. London Transport designed a new body to pair with the chassis and a new 9.6 litre engine (a vast improvement on the previous 7.7 and 8.8 litre engines). The objectives were increased performance, improved operating economy, ease of driving control and most importantly, simplified maintenance at minimal cost.

The new bus incorporated a 6 cylinder monobloc fitted with push rod operated overhead valves, hardened iron liners and two piece detachable head. The metalastic engine had a common axis of front and rear rubber supports passing through the centre of gravity, providing a true axial movement and eliminating vibration. The low rotational speed of the engine under moderate load factor was designed to increase the mechanical life – essentially the engine being de-rated.

The transmission by fluid flywheel uses a four speed pre-selective gearbox of AEC design, utilizing air-pressure controlled gear bands, eliminating starting jerks. Using high pressure air for gear band engagement also avoids the risk of slip when moving off or changing gear. Air pressure is used for brakes which controlled by the brake pedal, providing a soft feel for the first three-quarters of the pedal travel; the last quarter is heavily spring-loaded to discourage use except in emergencies, when full air pressure gives maximum retardation. The normal rated output of the engine is 100bhp at the maximum governed speed of 1,800rpm, at which the exhaust is intended to be smoke free. The compression ratio is 16:1 and the total engine weight being 13CWT (660KG), being made from the lightest materials available at the time.

The experimental stage (150 buses built with wooden framed composite bodies at Chiswick) had proved successful and after the end of the war, plans were made to resume production, but with some modifications. Front and rear bulkheads were added; the front bulkhead was situated at the front of the lower saloon passenger compartment and the rear bulkhead at the rear of the lower saloon. The chassis which ran the entire length of the bus was truncated at the rear bulkhead and a riser was inserted between the chassis and the body. Brackets attached to the front of the riser supported the platform and a battery riser running from the platform riser to the back of the bus added support for the battery crate and the rear of the body that was no longer directly supported by the chassis. The body framework transitioned from predominantly timber to steel channels with timber inserts (for screwing panels on) and steel stress plates. These modifications were to allow the bus to utilize a new overhaul system introduced by London Transport, where every 4 years buses would be easily separated from their chassis and both chassis (with mechanical parts) and body would undergo refurbishment and repair. A new Underground train depot at Aldenham which had become defunct since the introduction of the post-war Green Belt legislation was converted to a bus overhaul facility where London's buses would be despatched to on a pre-determined schedule and emerge as good as new. The RT fleet of nearly 7,000 buses all passed through Aldenham Works, which was also the site for accident damaged vehicle repairs and vehicle testing.

The demand for the new buses was overwhelming in the early fifties and consequently (and because London Transport had a policy of seeking additional suppliers) an order was placed for a Leyland variety. Based on a heavily modified Leyland PD2, they were immediately recognizable by their radiator grille which was rectangular without a centre strip, housed in the same RT shaped radiator block. They were designated RTL type and eventually totalled 1,631 in number. When bus dimensions size regulations were relaxed, Leyland produced an additional 500 that were six inches wider, designated RTW type.

The RT type fleet consisted of bodywork by different manufacturers. Some were indistinguishable from one another to the untrained eye and others were noticeably different. These included Park Royal Vehicles, Weymann, Saunders, Cravens and Metro-Cammell.

RT3316 was married with a Weymann body when built and later acquired the existing Park Royal body.

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