The Hawker P.1121 was a British supersonic fighter aircraft designed, but never fully completed, by Hawker Siddeley during the mid-1950s. It was designed by a team headed by Sir Sydney Camm. The P.1121 was initially funded as a private venture by Hawker Siddeley, with the aim of producing an aircraft that conformed with the requirements of Operational Requirement 339 (OR.339) by the UK Air Ministry.