The Cyclone engine series began in 1924 when the U.S. Navy Department contracted with the Wright Aeronautical Corporation for a nine-cylinder air-cooled radial engine of approximately the same displacement as the water-cooled Liberty engine of World War I. The first engine, known as the P-1, had a rating of 303 kW (406 hp), and gained favor among aircraft builders because of its fuel economy, long service life, easy and economical maintenance, and low weight/horsepower ratio. Through progressive improvements, the rating of later models was raised to an impressive 895 kW (1,200 shp) for takeoff.
Air-cooled radial engines like the Cyclone became the standard for naval aircraft, and also appealed to designers of commercial transports. With few exceptions, commercial aircraft relied on air-cooled radial engines until the advent of jet engines.
The Lockheed Sirius was powered by a 522.2 kW (710 hp) Wright Cyclone.
National Air and Space Museum, Smithsonian Institution