Hawker Siddeley (BAe), McDonnell-Douglas/Boeing Harrier AV-8S/TAV-8S & AV-8B/B+/TAV-8B

The Hawker P.1127 and the Hawker Siddeley Kestrel FGA1 were the experimental and development aircraft that led to the Hawker Siddeley Harrier, the first vertical and/or short take-off and landing(V/STOL) jet fighter-bomber. Kestrel development began in 1957, taking advantage of the Bristol Engine Company’s choice to invest in the creation of the Pegasus vectored-thrust engine.

Testing began in July 1960 and by the end of the year the aircraft had achieved both vertical take-off and horizontal flight. The test program also explored the possibility of use upon aircraft carriers, landing on HMS Ark Royal in 1963. The first three aircraft crashed during testing, one at the 1963 Paris Air Show.
Improvements to future development aircraft, such as swept wings and more powerful Pegasus engines, led to the development of the Kestrel. The Kestrel was evaluated by the Tri-partite Evaluation Squadron, made up of military pilots from Britain, the United States, and West Germany. Later flights were conducted by the U.S. military and NASA.
Related work on a supersonic aircraft, the Hawker Siddeley P.1154, was cancelled in 1965. As a result, the P.1127 (RAF), a variant more closely based on the Kestrel, was ordered into production that year, and named Harrier – the name originally intended for the P.1154 – in 1967. The Harrier served with the UK and several nations, often as a carrier-based aircraft.
Following the end of the Korean War, a number of aircraft companies in both Europe and America separately decided to investigate the prospective of vertical take-off and landing (VTOL) aircraft, which would eliminate the requirement for vulnerable runways by taking off and landing vertically as opposed to the conventional horizontal approach. In addition to military applications, the prospect of applying such technology to commercial airliners was also viewed with considerable interest by the mid 1950s, thus the value of developing viable vertical take-off systems was judged to be substantial. However, even during this era, few companies had envisioned that a VTOL aircraft would also be realistically compatible with the characteristics of high performance military aircraft.


In 1957, jet engine engineer Stanley Hooker of the Bristol Engine Company informed aeronautics engineer Sydney Camm of Hawker Aircraft that Bristol had been working a project that combined major elements of their Olympus and Orpheus jet engines to produce a directable fan jet. The projected fan jet harnessed rotatable cold jets which were positioned on either side of the compressor along with a ‘hot’ jet which was directed via a conventional central tailpipe. The original concept upon which the engine, which had been named Pegasus,  was based came from Michel Wibault, a French aviation consultant.  Several adaptions and enhancements were made by Bristol to reduce size and weight over Wibault’s original concept.
Around the same point as Hooker’s approach, Hawker had been working upon the development of a replacement fighter aircraft for the Hawker Hunter, designated as the P.1121. However, the P.1121 was cancelled shortly after the publishing of the 1957 Defence White Paper, which had advocated a policy shift away from manned aircraft and towards missiles. In light of this cancellation, Hawker found itself with the available resources to commit to a new project, and thus decided to study the use of the projected Pegasus engine as a basis for a new military aeroplane that would be able to conform with an active NATO specification that sought a new Light Tactical Support Fighter to replace the Fiat G.91, particular attention was paid to meeting the specification’s performance and load requirements.
According to Air Chief Marshal Sir Patrick Hine, Hawker’s interest may have also been stimulated by the presence of Air Staff Requirement 345, which sought a V/STOL ground attack fighter for the Royal Air Force (RAF).[9] Aviation author Francis K. Mason expressed a contrary view, stating that Hawker’s decision to proceed was independent of British government initiatives, and that the P.1127 project was primarily based upon the NATO requirement instead. Hawker had a keen ally in its development in the form of Bristol, but by that point the latter was experiencing financial difficulties, and the lack of foreseeable commercial applications for the Pegasus engine in particular, coupled with refusals from HM Treasury, mean that development would have to be financed by NATO institutions instead. The close cooperation between Hawker and Bristol was viewed by project engineer Gordon Lewis as a key factors which had enabled the P.1127’s development to proceed in spite of technical obstacles and political setbacks.