▁usually ▁heav ier ▁and , ▁in ▁the ▁case ▁of ▁the ▁Se af ire ▁XV / XV II ▁and ▁F . ▁ 4 7 ▁series , ▁they ▁were ▁very ▁different ▁aircraft ▁to ▁their ▁land - based ▁counter parts . ▁ ▁It ▁is ▁notable ▁that ▁throughout ▁the ▁entire ▁development ▁process , ▁which ▁took ▁place ▁over ▁twelve ▁years , ▁from ▁ 1 9 3 5 ▁through ▁to ▁ 1 9 4 8 , ▁there ▁were ▁no ▁out standing ▁fail ures ▁of ▁the ▁basic ▁design : ▁this ▁is ▁a ▁real ▁test ament ▁to ▁the ▁original ▁genius ▁of ▁Regin ald ▁J . ▁Mitchell , ▁his ▁successor ▁Joseph ▁Smith , ▁and ▁the ▁design ▁teams ▁they ▁led . ▁ ▁The ▁Roll s - Ro y ce ▁Mer lin ▁and ▁Griff on ▁engines ▁A ▁key ▁factor ▁which ▁allowed ▁the ▁continued ▁development ▁of ▁the ▁Sp it fire ▁was ▁the ▁development ▁of ▁progress ively ▁more ▁powerful ▁and ▁improved ▁engines , ▁starting ▁with ▁the ▁Roll s - Ro y ce ▁Mer lin ▁and ▁progress ing ▁to ▁the ▁bigger ▁and ▁more ▁powerful ▁Roll s - Ro y ce ▁Griff on . ▁The ▁evolution ▁of ▁high ▁oct ane ▁av iation ▁fu els ▁and ▁improved ▁super char ger ▁designs ▁enabled ▁Roll s - Ro y ce ▁to ▁extract ▁increasing ▁amounts ▁of ▁power ▁from ▁the ▁same ▁basic ▁designs . ▁For ▁example , ▁the ▁Mer lin ▁II ▁and ▁III ▁which ▁power ed ▁the ▁Sp it fire ▁I ▁produced ▁a ▁maximum ▁of ▁ 1 , 0 3 0 ▁h p ▁( 7 7 0   k W ) ▁using ▁the