In 1933, the Great Western Railway introduced the first of what was to become a very successful series of diesel railcars, which survived in regular use into the 1960s, when they were replaced with the new British Rail "first generation" type diesel multiple units. Design Bodywork The original design featured streamlined bodywork, which was very much the fashion at the time. The rounded lines of the first examples built led to their nickname: "flying banana". The preserved W4W is an example of the original, rounded body shape. Later "razor edge" examples, such as No. 27 (pictured), had much more angular (and practical) bodywork, yet the nickname persisted for these too. Heating The interiors of railcars No. 1 to No. 18 were heated by using waste heat from the engine cooling water. This system proved unreliable in service due to issues with the thermostat valves employed. Later vehicles from No. 19 onward abandoned this system to its unreliability and because their revised specification demanded that they be able to haul steam heated rolling stock. These later vehicles, No. 19 onwards, were equipped with steam heating systems. Which were capable of heating both the vehicles interior and that of any additional trailed vehicles, via a steam supply to the standard steam heating equipment. Steam was produced by a fully automatic Vapor Clarkson steam generator manufactured by Gresham and Craven Ltd under licence from the Vapor car co. The generator was of the water tube with counterflow arrangement type, and could supply up to 300 lb of steam per hour, at 45 lb per square inch. The quantity of steam supplied could be varied by the driver to suit the demand required by a solo railcar, or plus one, or plus two, trailer vehicles. The fuel used was the same diesel used for the railcar's engines. However, it was stored in a separate 45 gallon tank. The water supply for the heating system consisted of a single 100 gallon tank. Powertrain Railcars No. 1 to No. 18 were powered by a high speed diesel engine manufactured by A.E.C, producing a maximum brake power output of 130 hp (97 kW). The engine was of the straight 6 configuration, with a bore of 115 mm diameter and a stroke of 142 mm. This gave a total displacement of 8.85 litres. The maximum operating speed was 1,800 rpm. Railcars No. 19 onwards were powered by a