Before each level begins, the commander in charge will give you a brief story of what's going on and an overview of your mission objectives for the level you're about to bravely challenge. You can perform your missions in any order you want, but it's best (and easier) to do them in order.
At the start of each level, the helicopter you have the honor of controlling will be sitting on a frigate in the ocean. You have to fly over the crystal blue ocean to the sandy land to make the action begin. Each of the four levels takes place in the desert, but they're not all the same. The territories in each of the four not so deserted deserts are different, and they get more full of enemies and complicated as you go along.
There are many different kinds of enemies in each level. There are men loaded with guns, bazooka-wielding men, enemy choppers, speedboats, various kinds of tanks, and other powerful, ground-residing nightmares.