Question: Looking for movie featuring Dragons vs. Navy (or Army, but the trailer featured battleship trying to shoot the dragons down).

Trailer also showed a dogfight between helicopters and dragons, capping (on the trailer) with a dragon setting a Blackhawk's blades on fire.

Answer: 
I saw that trailer too and then could not find it again , but stumbled across it today ,it is called Crimson Skies 

Only other info i could find on this is that it was originaly called Dragon seige but your guess is as good as mine as to wether its movie or game
This sounds very like the British film [Reign of Fire](http://en.wikipedia.org/wiki/Reign_of_Fire_%28film%29), which included several scenes of fire-breathing dragons versus helicopters.

The trailer is [here](https://www.youtube.com/watch?v=Wg7bjwEXp7Y) and although there are various helicopter shots there's nothing specifically with the blades on fire.