▁attack ▁run , ▁the ▁aircraft ▁would ▁be ▁able ▁to ▁return ▁to ▁its ▁base ▁by ▁making ▁use ▁of ▁the ▁secondary ▁jet ▁prop ulsion ▁instead . ▁ ▁Although ▁the ▁SR . 5 3 ▁proved ▁to ▁have ▁prom ising ▁performance ▁during ▁test ▁fl ights , ▁the ▁requirement ▁for ▁such ▁an ▁aircraft ▁had ▁been ▁over t aken ▁by ▁rapid ▁adv ances ▁in ▁surface - to - air ▁miss ile ▁technology , ▁leading ▁to ▁re cons ider ation ▁of ▁the ▁aircraft ' s ▁purpose . ▁In ▁July ▁ 1 9 6 0 , ▁the ▁development ▁programme ▁was ▁formally ▁cancel led , ▁by ▁which ▁time ▁a ▁total ▁of ▁ 5 6 ▁test ▁fl ights ▁had ▁been ▁performed . ▁A ▁pair ▁of ▁prototype ▁SR . 5 3 ▁aircraft ▁had ▁been ▁completed ▁and ▁used ▁during ▁flight ▁tests . ▁One ▁of ▁these ▁was ▁destroyed ▁during ▁one ▁such ▁test ▁flight ▁in ▁June ▁ 1 9 5 8 . ▁The ▁other , ▁the ▁first ▁prototype , ▁surv ived ▁and ▁was ▁preserved ; ▁it ▁is ▁currently ▁on ▁public ▁display ▁at ▁the ▁Royal ▁Air ▁Force ▁Museum ▁Cos ford . ▁ ▁Design ▁and ▁development ▁ ▁Background ▁The ▁Second ▁World ▁War ▁had ▁demonstrated ▁the ▁importance ▁of ▁strateg ic ▁bomb ing ▁to ▁modern ▁war fare , ▁and ▁as ▁the ▁emer ging ▁Cold ▁War ▁developed , ▁the ▁development ▁of ▁new ▁and ▁more ▁effective ▁air ▁def ences ▁against ▁large ▁waves ▁of ▁host ile ▁bom ber ▁aircraft ▁armed ▁with ▁nuclear ▁weapons ▁became ▁a ▁priority ▁for ▁many ▁nations . ▁During ▁the ▁war , ▁Naz i ▁Germany ▁had ▁extens ively ▁developed ▁its ▁own ▁ro