Building war-planes requires two buildings, LVL 2 Aviafactory and an Airfield. The Airfield has 4 slots for warplanes, and you can use it for any combination of Vertex's and Thor's. The Airfield is also a great target for enemy bombers in case planes are on the ground. Other than that, Airfield serves no other purpose.
Upgrade priority for Airfields is as follows:
- Rapid Service System
- Advanced Repair System
- Hardened Ceramic Armor
- Building Construction
Warplanes are based on an Airfield. They are repaired and refueled there.