Farnborough Radar one day; I saw a '7000' squawk appear near Winchester moving quite fast and indicating about 2,000ft climbing. It was tracking north east and as it climbed, it's altitude readout indicated it had entered controlled airspace. It eventually levelled off at FL170 but when it got overhead Heathrow, suddenly went into an orbit. About this time, D & D phoned to say a Sea Harrier was overdue at Yeovilton and was last seen heading towards the London area. We pointed out the 7000 squawk which by this time had turned onto a reciprocal of its original course and was heading towards us. Sure enough, when it got overhead (still indicating FL170) it went into an orbit again and its altitude readout started unwinding at high speed, so much so that the tower controller scrambled our fire service assuming it was crashing. Anyway a Sea Harrier appeared in the circuit and levelled off, did a quick circuit on runway 25 (we'd put all the lights on) and then landed. At the time, our Landrover was equipped with a 'Follow Me' sign and he wasn't far from the runway so positioned himself near one of the turnoffs to lead ot to a parking area.
Turned out it was a USMC pilot on exchange; he'd had radio failure over the sea south of Cornwall/Devon then headed north east to try to find Yeovilton. Seeing Southampton Water, he assumed it was Plymouth Sound so continued on the same track, only becoming suspicious when he saw a large airfield below him with airliners parked all over it. Then he headed south west, saw Farnborough with military type aircraft parked and made a dive for it.
He hadn't a clue where he'd landed until the groundcrew told him after he'd shut down.
They wouldn't let him fly back to Yeovilton either; sent up a 2 seater with a spare pilot to ferry his aircraft back and he returned in the back seat.