20 The Rolls Royce Merlin, game changer.
Two of my uncles were engineers on this engine design, one later developed the 'sand trap' for use in Africa (no, not just a filter). They moved to Canada and worked for A.V. Roe as chief engineers integrating the Iroquois engine on the Arrow. My father also worked there and met my mom through them. Pretty cool having a historic background of conception, unlike most of you slugs. ;)