Helicopters are very good against Infantry and Militia. Therefore a very good choice for taking out the Netrual cities, before sending in your own Troops to conquer it. They can also be used to transport Marines if you use the Desert Storm strategy. Helicopters are unlockable by tweeting Atwar on Twiter or signing up on their facebook page. Helicopters are powerful units but it is a bad idea to send them out for defense against tanks or aircraft. They also happen to be somewhat expensive. Deploying them to crush infantry or militia is better.
Their slow range can be a burden sometimes. Helicopters, while faster than tanks and infantry, are slower than any other type of aircraft.