Helicopters are your first long ranged units, and perhaps the only early tier unit you will continuously build and use later on in the game. They are not particularly deadly or sturdy, but amassed helicopters supported by defense grid can destroy enemy attacks with ease. Good vs mid ranged units, weak vs short ranged units. Helicopters are the most important units in the game, even above jeeps.
Helicopters should be used with Artilleries when attacking and NPC 27 or below (more Helis)
With a aircraft commander they are super effective