Rule changes for 1920

[Guinness]

So since I opened up that can of worms, what should we be looking at? I'll start and maintain a list of general subjects here, but open up threads for such topics in the General Army/Air Forces/Navy or Geography and Economics forums as necessary.

Things I know people want to talk about now include:
- Overhauling the Aircraft and Airfield construction and upkeep rules, etc.
- Fortification upkeep costs