 The aircraft's design parameters were purposely designed around a top secret, untested, 24-cylinder, 2,450 hp liquid-cooled Napier Sabre engine.Although originally proposed to the Air Ministry and receiving approval as primarily an engine programme, the Napier-Heston Racer was ultimately not officially sanctioned and had to proceed as a private venture with Lord Nuffield entirely underwriting the project.The first aircraft of two planned for the record attempt, registered G-AFOK (call sign "Fox Oboe King"), had its maiden flight at Heston Aerodrome on 12 June 1940, piloted by Squadron Leader G.L.G.