The reciprocating sleeve valves were open-ended, rather than sealing in a junk head. The open end uncovered the exhaust ports high in the cylinder wall at the bottom of the sleeves' stroke, leaving the ports cut into the sleeve to handle the incoming charge only. The sleeves had a stroke of 30% of the piston travel at 1.950 in (49.5 mm) and operated 15 degrees in advance of the crankshaft. The Crecy sleeve valves were of similar construction but differed in their operation compared to the rotary sleeve valve design that was pioneered by Roy Fedden, and used successfully for the first time in an aircraft engine, the Bristol Perseus, in 1932.