Battle of Britain is a set of free wargames rules for operational level games. The authors write:
This is a fast playing operational level game about the German air raids over England on August 8th, 1940. Designed for group or convention play where players are in charge of the various sectors or Luftwaffe raids and it can be completed in a few hours. This PDF includes the rules, a map, markers, cards, and aditional materials needed to play the game.