The shortest distance between two points is a straight line, which gives every air unit an inherent advantage. Even the slowest-moving gunship can bypass cliffs and canyons, making flying units an obvious choice for crippling raids on enemy bases. Of course, not every air unit is designed for combat. Both factions use air-based support units to heal units and structures. Even if you favor other unit types, you’d do well to begin producing air units as soon as you can.
Halo Wars 2 eGuide Units Air Units