▁ ▁and ▁the ▁Arm strong ▁Sid de ley ▁Sn ar ler ▁with ▁ ▁of ▁thrust ; ▁these ▁ro cket ▁mot ors ▁made ▁use ▁of ▁different ▁prop ell ants , ▁the ▁Spr ite ▁used ▁a ▁high - test ▁per ox ide ▁( H TP ) ▁mon op rop ell ant ▁while ▁the ▁Sn ar ler ▁har ness ed ▁a ▁m eth an ol / water / liqu id ▁o xygen ▁mix . ▁During ▁the ▁early ▁ 1 9 5 0 s , ▁both ▁engines ▁proceeded ▁to ▁the ▁flight ▁testing ▁phase ; ▁however , ▁some ▁of ▁the ▁demand ▁for ▁their ▁role ▁to ▁provide ▁f igh ters ▁with ▁increased ▁performance ▁was ▁soon ▁being ▁met ▁by ▁the ▁increasing ▁pre val ence ▁of ▁ ▁conventional ▁jet ▁engines ▁being ▁equ ipped ▁with ▁re he at ▁instead . ▁ ▁In ▁May ▁ 1 9 5 1 , ▁faced ▁with ▁reports ▁on ▁the ▁increasing ly ▁potential ▁cap ability ▁of , ▁and ▁thus ▁the ▁threat ▁pos ed ▁by , ▁the ▁growing ▁Soviet ▁strateg ic ▁bom ber ▁fleet ▁and ▁that ▁nation ' s ▁newly ▁developed ▁atomic ▁weapons , ▁the ▁British ▁Air ▁Ministry ▁proceeded ▁to ▁draft ▁an ▁Oper ational ▁Re quire ment , ▁OR ▁ 3 0 1 , ▁which ▁sought ▁a ▁ro cket - power ed ▁inter ceptor ▁that ▁could ▁att ain ▁an ▁alt itude ▁of ▁ ▁in ▁just ▁ 2 ▁minutes ▁ 3 0 ▁seconds . ▁Many ▁of ▁the ▁performance ▁requirement ▁laid ▁out ▁by ▁OR ▁ 3 0 1 ▁was ▁due ▁to ▁the ▁anticip ation ▁of ▁rapid ▁increases ▁in ▁performance ▁by ▁the