From Wikipedia
Their Finest Hour is a World War II air-combat flight simulation video game , released in October 1989 by LucasFilm Games.
It was the second of a trilogy of World War II titles by LucasFilm Games, the others being "Battlehawks 1942" (1988) and "Secret Weapons of the Luftwaffe" (1991). The simulation was a recreation of the tactical and strategic considerations of the Royal Air Force and German Luftwaffe during the Battle Of Britain from July to September 1940. The game was released with a 192-page manual, that provided a detailed historical overview of the battle and pilots' perspectives, both RAF and Luftwaffe. The game pioneered gameplay elements featured in later Lucasfilm releases, such as a mission builder and combat film recorder, the ability to man all the crew positions in a bomber, and a Campaign mode where the historical outcome is decided by the success or failure of the missions flown by the player.