One of 9 Kestrel FGA.1s built as development aircraft between the experimental P.1127s and the production Harriers, first flying in 11.64 as XS694, then being transferred to the US Army for evaluation as 64-18266. Apparently became the second NASA 520 when the first (ex XS694/64-18268) crashed, substantial parts from the latter being used to make it airworthy again for NASA research use at Langley. They also had NASA 521 (ex XS689/64-18263, now displayed at the nearby Virginia Air & Space Center