As part of his duties, Bentley was dispatched to Gwynnes’s factory in London to improve the reliability of their license built Clerget 9B rotary engines.

The 130 horsepower Clerget 9B powered a number of important British aircraft, including the Sopwith 1½ Strutter however in service it was prone to overheating and seizure due to the failure of piston obturator rings.

[2] Following technical disagreements with Gwynnes’s management, who were resistant to some of his ideas, Bentley was reassigned to work with Humber engineering whose wartime production up until that point had mostly consisted of bicycles and field kitchens.

[2] At Humber’s works, Bentley was able to implement his ideas resulting in a rotary engine which, while outwardly similar to the Clerget 9B, featured aluminium cyliners and redesigned cylinder heads.

[3][4] The engine retained the Clerget’s signature offset epicyclical cam gears with separate pushrods for the intake and exhaust.