Britain came within one government decision of fielding a supersonic Harrier. Not a paper study: a funded aircraft with an engine on a test stand and three airframes being built. It was called the Hawker Siddeley P.1154, and the reason it does not exist is not that the engineering failed. It is that two customers wanted two different aeroplanes and a minister insisted they have the same one.

The idea: an afterburner for the cold air

The Harrier’s Pegasus engine splits its exhaust between four rotating nozzles: two hot at the back, two cold at the front carrying bypass air. That layout works beautifully and caps the aircraft firmly below the speed of sound.

Plenum chamber burning was the way through. It is an afterburner that acts only on the bypass air leaving the front nozzles, adding thrust where the aircraft needs it most in the hover and giving enough total thrust for supersonic flight. Bristol Siddeley built it into the BS.100, an engine combining elements of the Olympus and the Orpheus, with rotatable cold jets either side of the compressor and hot jets through a bifurcated tailpipe. The production version was designed to deliver around 150 kilonewtons, roughly 33,000 pounds of thrust.

Bristol first ran a plenum-chamber-burning Pegasus 2 in December 1962. The Minister of Aviation, Julian Amery, selected the BS.100 for the P.1154 on 25 March 1963. The engine itself first ran on 30 October 1964.

It was not a free lunch. Burning fuel in the cold stream and pointing it at the ground produces extraordinary erosion of whatever surface you are hovering over, which was one of the practical problems nobody had fully solved.

Winning a competition that bought nothing

NATO issued Basic Military Requirement 3 in August 1961: a supersonic V/STOL strike fighter with a 460 kilometre combat radius, cruising at Mach 0.92, dashing at Mach 1.5, and able to clear a 15 metre obstacle after a 150 metre takeoff roll carrying 910 kilograms.

Hawker Siddeley submitted the P.1154 in January 1962. By May it had been judged the technical winner from eleven entries, with the Dassault Mirage IIIV named as the secondary design. And then nothing happened, because NATO had no central procurement budget. Winning the competition entitled the aircraft to be bought by individual member nations, and none of them did.

Two services, one airframe, no chance

The British programme had already acquired its fatal complication. On 6 December 1961 the P.1154 was designated for joint RAF and Royal Navy development, and by March 1962 the Ministry of Defence was considering it as the replacement for both the RAF’s Hawker Hunters and the Navy’s de Havilland Sea Vixens.

Those are not the same aeroplane. The RAF wanted a single-seater. The Fleet Air Arm wanted a two-seat interceptor, because intercepting things over the sea at night is a two-person job. Hawker Siddeley sensibly proposed two variants. The Navy then objected to the tandem undercarriage as incompatible with catapult operations, and a tricycle arrangement was accepted instead.

Then, in May 1963, the Secretary of State for Defence, Peter Thorneycroft, insisted on one common aircraft for both services. He had been impressed by the American F-111, which was being sold on exactly that promise of multi-service commonality. The services agreed to complete commonality apart from their radars.

By July 1963 the weight was climbing because of naval modifications. By August, Hawker Siddeley was warning that the changes were damaging export prospects. The Navy had come to regard the aircraft as a second-rate interceptor; the RAF was openly unhappy about the strike performance it had given up. In October 1963 the Ministry of Aviation concluded that combining the strike and fighter roles in one airframe for both services was unsound.

The Sunday Telegraph announced the end of the bi-service aircraft in November 1963. On 26 February 1964 the Conservative government salvaged what it could: a development contract for an RAF-only P.1154 with the BS.100, while the Navy would get Phantoms re-engined with Speys.

Traded for an aeroplane that also died

In November 1964 Harold Wilson’s incoming Labour government told the Air Staff to prepare to cancel two of its three big development programmes: the P.1154, the BAC TSR-2 and the HS.681 transport. The RAF had to choose, and it chose to protect the TSR-2.

The P.1154 was terminated on 2 February 1965, on the grounds of cost, with at least three prototypes at various stages of construction. The TSR-2 was cancelled on 6 April 1965, nine weeks later.

The RAF bought Phantoms. And the government, in one of the more sensible decisions of the period, funded continued development of the unglamorous subsonic P.1127 instead. That aircraft became the Harrier, served for decades, went to war in the South Atlantic, was bought by the United States Marine Corps, and is the direct ancestor of the lift system on the F-35B.

It also took the name. Harrier had been reserved for the supersonic aeroplane.

Whether the cancellation was a tragedy depends on how much credit you give the engineering. Every other nation that tried supersonic vertical takeoff in this period, including the French with the Mirage IIIV, the Germans with the VJ 101 and later the Soviets with the Yak-41, spent a great deal of money and fielded nothing. Britain is the only country that came out of that era with a V/STOL combat aircraft that actually worked for forty years. It just was not the one it set out to build.

The P.1154 story in detail, including the engine and the inter-service argument that ended it.

A 1988 documentary on the Harrier, the aircraft that survived the cull.

Period 1981 coverage of the Harrier in service, a decade after the P.1154 was abandoned.

Sources: Wikipedia’s Hawker Siddeley P.1154 article and its cited sources, including Derek Wood’s account of the programme and Tony Buttler on British secret projects; Fleet Air Arm Museum for the surviving BS.100. Note: no photograph of a completed P.1154 exists, because none was finished.