The Kestrel.

[BOAC]

Which airfield was the Sqn based at?

- West Raynham I recall.

EDIT: Courtesy of Google and Harrier.org:

"The first of the Tripartite evaluation aircraft flew in March 1964, the others following along at regular intervals until the last flew in March 1965. Initially these aircraft were known as P.1127s but in November 1964 they were given the name Hawker Siddeley Kestrel FGA Mk.1. Not only did the Kestrel have many of the limitations of the P.1127 removed, it was also, like the earlier aircraft, fully stressed for combat operations, with provision for extra pylons and equipment, such as a Doppler navigator and auto-stabiliser - in fact, it was essentially the aircraft the RAF would have received had they pursued GOR345. However, as money was limited for the trials, this equipment was never fitted. The Tripartite programme involved pilots from the RAF, Luftwaffe, and three US services - Army, Navy and Air Force. Training on the Kestrel began at Dunsfold in the latter part of 1964, with the Tripartite squadron officially forming at RAF West Raynham on 1 April 1965. The objective of these trials was to establish the ground-rules for the operation of jet V/STOL fighters. This meant that emphasis was placed on operating techniques such as short take-off, dispersed site operations and concealment, rather than on flying attack missions. Although such sorties were simulated, no weapons were ever carried by Kestrels. In total 1,367 sorties were flown during the trials, which lasted until 30 November 1965. A huge amount was learnt about operations in the field, including the effects of hot gas re-ingestion, ground erosion and ways to alleviate both effects."