Build Airfield (Ctrl-Shift-A) Airfields function in the same manner that a city with an airport would for air units. They can be built after the discovery of Flight. Build Outpost (Ctrl-O) Outposts eliminate fog of war in neutral or owned territory. They can be built after the discovery of Masonry. Build Radar Tower (Ctrl-T) Radar towers provide a combat bonus to units within their affected area. They must be built within your territory. They can be built after the discovery of Advanced Flight.