Since its formation as a statutory corporation in 1933, the London Passenger Transport Board had a 30-year contractual obligation to source 75% of its buses from AEC, and in 1938–39 worked with AEC on a revised version of the Regent to better suit London operating practice, following on from the 100 experimental STD Titan TD4s of 1936. It had a large-displacement engine running under less stress, with other innovative features being an air-pressure system, not only working the brakes, but also the change-speed pedal on the pre-selective gearbox, which was built by AEC to Self-Changing Gears and Daimler Company patents. This was coded RT and the initial 151 built had LT chassis codes 1RT and 2RT and entered service between early 1939 and early 1942.
