Description from the rulebook:
This is a two-player scenario for the Europa system of conflict simulation [...]. It requires the use of maps/counters in the Europa game Their Finest Hour and the air rules and OB/OAs (Order of Battle/Order of Appearance) which are part of this package. It also requires that a number of air counters be made/modified to show the different sizes of air units used (squadron/staffel, wing/gruppe, group/geschwader) and base units. Battle of Britain simulates the air war over England and the attempt by the Luftwaffe to prepare for the possible invasion of England (Operation Seeloewe) in the late summer of 1940. It involves air combat only and is therefore suitable for assimilation of the unofficial 'Bro'Air Rules, which differs considerably from the originals. Use of the original air rules is not recommended for the purpose of this scenario.[...]
The game begins with the Aug II 40 ('Adlertag') turn and ends with the Oct 40 turn, lasting five full Europa turns.