How would mature Napier Sabre plans sent to prewar Britain affect the coming war?
Short answerThey could produce more powerful British fighters earlier, including improved land and naval aircraft.
NotesA mature Napier Sabre and detailed construction instructions could give Britain much more powerful fighters by 1940. A Sabre-powered Fulmar might appear, or Firefly development could move forward. A Spitfire designed around the engine is another possibility. The hypothetical engine is a developed version whose early problems have been resolved.