Now that's strange, I put in another clue yesterday and it dropped the entire post. Let's try this again:
Ken, the Hurricane was developed due to a specification put out by the RAF, as was the Spitfire
MJD, no, but you're closer so that means it's time for another clue:
Everyone is familiar with the V-12 powered aircraft of WWII but what was the first V-12 powered aircraft to see combat and who built it's engine?
1) It was an unsolicited product designed as an upgrade to a proven combat aircraft
2) It was used by several nations for over a decade after the end of hostilities(this was yesterday's clue)
3) It was used as a multi-role aircraft