The Castle Motor Co. was owned by the brothers Stanley and Loughton Goodwin, who made gun carriage hubs, shells and aero-engine components during World War I. Like so many others, they hoped to cater for the postwar demand for popular cars, their choice being a 3-wheeler with single wheel at the rear. They aimed to 'Rolls Royce the Morgan’ and to that end the engine had 4 cylinders, which was unusual when nearly all rival 3-wheelers relied on 2-cylinder power. The first 12 cars had 1094cc Dorman units, after which they turned to the Belgian-made 1207cc Peters. Transmission was by epicyclic gears, and the rear wheel was driven by shaft. The epicyclic transmission was listed through the car’s life, but at least some of the later cars, including one of the two known survivors, had proprietary 3-speed gearboxes. The Castle Three was a quality small car, and this was reflected in the 2300 orders which were taken at the 1919 Olympia Show. However, production was slow to start, and only about 350 were delivered in all, before the Goodwins sold their works to a local carpet firm. A prototype 4-wheeler, the Castle Four, never went into proction.