See Fedden.

Sir Roy Fedden is another English personality in the world of aeronautical engineering.

-He had an important participation in the development of engines during World War II

“Roy Fedden engine”

-Around 1946, at the end of the conflict he founded his own company, Roy Fedden Ltd. in Stoke Orchard, near Cheltenham, starting with two small units.

-The engine shown in the photograph gave 160/185 HP depending on whether or not it had reduction gear. There also was a major series of sliding-sleeve valve engines, which were another variant.

From Appendix 6: We have obtained two side views of the 6A1D-325 sliding sleeve engine.

“Roy Fedden horizontally opposed six-cylinder engine”