From back of the game box:
The German war machine has humbled all of europe - except Great Britain. Now, the mighty Luftwaffe plans to soften up Southern England for an invasion called Operation Sea Lion. And the RAF must wage a deperate defensive battle against a numerically superior foe.
Graphically stunning, historically accurate, and thrillingly realistic, Their Finest Hour: the Battle of Britain resets the stage for the air confrontation of the century.