The Airstrip, also known as the proving grounds, is buidable from  onward by all factions.
- Balloon  A slow-moving unit with plenty of LOS, but with very poor speed and armour, but a medium-strength suicide attack. Can be upgraded to airship for better armour, hitpoints, and a seriously powerful bomb attack. Doesn't require Military, only Academic Disciplines from University. These units have a hefty pricetag, and are vulnerable to arrow-wielding units so you're better off holding them until they can be upgraded.
- Biplane  Light aircraft capable of strafing enemy aircraft and units with bullets. Requires Deep Operations from Library, and Propulsion Systems from the MIC.
- Heavy biplane  Slightly more hitpoints and armour than biplane and armed with a bomb attack. Available only after Fortifications III researched.
- Airship .  Upgrade of Barrage balloon once Aeronautical Engineering researched. Airships deal serious damage to ships and buildings, but are vulnerable to anti-aircraft guns. Each airship you control results in a -1 happiness penalty to nations at war with you.