The Letov Š-31 was a fighter aircraft produced in Czechoslovakia in the early 1930s in a number of variants. All of the aircraft had metal tubular framing and fabric covering with a metal engine cowling.

The Bristol Mercury is a British nine-cylinder, air-cooled, single-row, piston radial engine. Designed by Roy Fedden of the Bristol Aeroplane Company it was used to power both civil and military aircraft of the 1930s and 1940s. Developed from the earlier Jupiter engine, later variants could produce 800 horsepower (600 kW) from its capacity of 1,500 cubic inches by use of a geared supercharger.