▁the ▁release ▁of ▁the ▁defined ▁Spec ification ▁OR ▁ 3 3 7 . ▁The ▁changes ▁of ▁the ▁defined ▁specification ▁mainly ▁revol ved ▁around ▁arm ament ▁changes , ▁adopt ing ▁the ▁Blue ▁Jay ▁inf ra red - gu ided ▁air - to - air ▁miss ile , ▁which ▁replaced ▁the ▁originally - en vis aged ▁ret ract able ▁battery ▁of ▁ ▁rock ets . ▁During ▁the ▁first ▁four ▁months ▁of ▁ 1 9 5 3 , ▁Sau nd ers - R oe ▁had ▁to ▁perform ▁a ▁struct ural ▁red es ign ▁of ▁the ▁SR . 5 3 ' s ▁fus el age , ▁wing , ▁and ▁under car riage ▁due ▁to ▁a ▁determ ination ▁by ▁the ▁Royal ▁A ircraft ▁Est ab lish ment ▁( RA E ) ▁that ▁the ▁wing ▁required ▁a ▁greater ▁an hed ral ▁angle ▁than ▁had ▁originally ▁been ▁designed ▁for . ▁ ▁On ▁ 5 ▁May ▁ 1 9 5 3 , ▁an ▁advis ory ▁design ▁conference ▁was ▁hosted ▁at ▁the ▁Ministry ▁of ▁Supp ly ▁foc using ▁on ▁the ▁SR . 5 3 ; ▁three ▁days ▁later , ▁a ▁formal ▁contract ▁for ▁the ▁production ▁of ▁the ▁three ▁pro tot ypes ▁was ▁received . ▁Due ▁to ▁doub ts ▁within ▁the ▁R AF ▁and ▁the ▁Ministry ▁over ▁the ▁correct ▁fuel / mot or ▁to ▁select ▁for ▁the ▁aircraft ▁in ▁order ▁to ▁meet ▁the ▁Spec ification , ▁it ▁was ▁decided ▁to ▁issue ▁a ▁modified ▁specification , ▁and ▁later ▁a ▁development ▁contract , ▁to ▁A . V . ▁Ro e , ▁who ▁comm enced ▁work