We have "Jetman," who is clearly inspired by The Rocketeer. We have Sky Captain's P-40. We have a whole load of purely "what-if" aircraft. Now, I'd like to share another odd alternate history with some appealing designs and themes that could be carried over into BAT. Is the main character's plot realistic? Nah. Is the setting realistic? Probably not. But it sure is intriguing.
Codename Eagle An FPS game released in 1999, set in an alternate history where WWI and the Russian Civil War never happened. The reasons are left vague at best, but it can be assumed that, at the very least, the Russo-Japanese War had a different outcome and Archduke Franz Ferdinand was never assassinated.
In 1917, assassins kill Tsar Nicholas II and most of his family, but two of his children, Alexei (referred to as Alexander) and Anastasia, are rescued. They are hypnotized to forget their true selves in order to further protect their identities. General Popov, the traitor that facilitated the assassination and covered it up as a tragic accident, presents Lieutenant Oleg to the Russian people, claiming that his name is Peter and is the sole surviving heir of the late Tsar. The treasonous duo transform the Empire into a military superpower, leading a brutal conquest against most of Europe and the Middle East. The remnants of the free European nations form an alliance and organize an army of elite commandos, the Shadow Command, to resist the might of the corrupt Russian Empire.
Fast forward to 1927, and Alexander, still unaware of his true past and known simply as "Red," is an agent of the Shadow Command. Through the missions he carries out and the people he meets, he slowly remembers his royal heritage. However, having served with the Shadow Command for years and desiring to remain in service with his comrades, he asks his sister Anastasia to reveal the truth of the coup to the people and take the throne as Tsarina of Russia. After assassinating "Tsar Peter," Red manages to stop Popov from attacking London with a "doomsday device" (presumably a nuclear weapon) delivered via airship, and secures his nation's future under Tsarina Anastasia.
Mark V tanks are given a more modern turret, helicopters and ballistic missiles are invented early, Russian vehicles and such seem notably German and French (presumably due to their conquest of Europe), and so on. The actual in-game vehicles are significantly different from those in the intro cinematic, but both the intro and in-game designs are very rugged and fitting.
As an interesting side note, the developers of Codename Eagle would use the experience of programming the game's engine with its unique weapon and vehicle mechanics in their next major gaming venture, Battlefield 1942, kicking off the immensely popular (and lately declining) Battlefield franchise.