sentences:  It was later used to test retractable Fairey-Youngman flaps to be used on the Fairey Firefly fighter.In 1938 the first prototype P4 was at RAE Farnborough, where it was used for testing the effects of barrage balloons – by deliberately flying into a weighted cable hung beneath (not the actual tether cable).The tests were carried out at RAF Lakenheath (Pawlett Hams from September 1939), with a Battle ‘chase plane’ from RAF Mildenhall filming the process.