Hawker P.1121 Staff having been unable to understand the concept of the multi-purpose functionality of the aircraft, which would become commonplace on later aircraft. While seeking a new project to take the place of the P.1121, Camm soon began work upon another new and radical aircraft design, designated as the Hawker Siddeley P.1127. The P.1127 would become the Hawker Siddeley Harrier, the first effective vertical take-off and landing (VTOL) combat aircraft. The Hawker P.1121 was envisioned as being one of the first British-built supersonic fighter aircraft, being projected to be capable of speeds of up to Mach 2.5. It was to have
British Aerospace Harrier II experience had highlighted demand for a more capable aircraft. The British government had only a minor requirement, for up to 60 Harriers at most and competing pressures on the defence budget left little room for frivolous expenditure such as the Advanced Harrier. A lack of government backing for developing the necessary engine of the new aircraft, the "Pegasus 15", led Hawker to withdraw from this project in 1975. Due to US interest, work proceeded on the development of a less ambitious successor, a Harrier fitted with a larger wing and making use of composite materials in its construction. Two prototypes