Airfields function in the same manner that a city with an airport would for air units. To construct an Airfield, move a worker to any neutral or owned land tile and select the Build Airfield unit action. Construction of the Airfield consumes the worker. Airfields can be a re-base mission destination. All air missions can be launched from an airfield, and there is no limit to the number of aircraft that can be re-based at an Airfield. Airfields can only be used by the player who created it. If it falls into the territory of another civilization, however, the airfield becomes solely useable by the player whose territory it lies in (unless they have yet to research Flight, in which case the airfield is destroyed). Airfields can be pillaged like a terrain improvement, which also destroys the airfield. Airfields can only be built in tiles that have no other improvements, an airfield, a colony, a road or a railroad. The "Build Airfield" unit-action becomes available after the Flight advance is researched.