From Nothing But Shooters (NBS):
"Coral Sea (complete with Air Superiority Mode) was recently unlocked due to the amount of people playing and racking up kills. The creators of BF 1943 wanted to keep this map sheltered until the community reached 43 million kills - this was achieved in just 5 days on Xbox Live. As Coral Sea is an airplanes-only map, all of the fighting takes place in the sky. If you're the type that likes to fly a plane and partake in dogfights, then this map was made for you."