In 1934, the GWR introduced its first four-axle, lightweight high-speed diesel railcar. Built by Park Royal, it was powered by a 130-hp AEC diesel engine. Due to its streamlined body, it was also called “Flying Banana”. After this one, 17 more were built with two of the same engine which could reach 80 mph. All these had a heater that used the waste heat from the engine.

Railcars 19 to 38 had a more angular exterior and two engines of a direct-injected variant that only provided 105 hp each. Since the requirement now was to be able to haul a regular passenger coach, they had a steam heating boiler that supplied both the interior of the railcar and the additional coach.

With their high speed and low capacity, they were used for businessman's services, some on lines of more than 100 miles. Two railcars were built for parcels service and could be recognized by a lower number of windows. The last three were built as double units which only had one cab per car and often had a corridor coach between them. They were scrapped between 1954 and 1962 after being replaced by the first generation DMUs. Today, three are being preserved, with only No. 22 in operational condition.