The main runway has the unique Vertical Take Off Grids (VTO Grids or Hover Grids) – used for the tethering of jump jets such as the Harrier whilst hovering. These are located on aprons that adjacent the main runway and are within the Operational Readiness Platform [ORP]. Beneath these gratings is a large void chamber to take the hot air, condensation and gases from the downdraft of the jet engines of the aircraft. Within the eastern Engine Testing Pen there is a similar arrangement that is a unique feature to Dunsfold.
The Hawker P.1127 and the Hawker Siddeley Kestrel FGA.1 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.