Although the static air-cooled radial engine is by no means an innovation irr the history of aero-engine development, its career has been somewhat chequered. Some ten years ago several practical comparatively low-powered air-cooled radials were produced and successfully flown, but they were ousted by the rotary engine on the score of power/weight ratio.

When in 1917 it was found that the limit of the air-cooled rotary had been reached, a demand arose for an engine of the same characteristics of manoeuvrability, compactness and light weight as this type, but of much higher power, and with a general all-round performance and fuel consumption comparable with the water-cooled engine of that date.