Some seven thousand buses of the RT family were built for London Transport between 1939 and 1954 creating the most standardised bus fleet in the world, although a number of design improvements and variations evolved as production progressed. The majority were finished in Central Area red livery, although many were painted green for Country Area and Green Line use.
Most were were based on the AEC Regent MkIII chassis built at Southall, being fitted with AEC 6-cylinder 9.6 litre engines. Transmission was through a four speed air operated pre-selective gearbox with fluid flywheel.
The majority were bodied by Park Royal Vehicles or Weymann.
The type proved immensely efficient and reliable, and some remained in public service with London Transport until as late as 1979.