This achievement is for completing the fifteenth mission of the game and can be obtained on any difficulty.
Here's my playthrough of Mission 15 Battle for Farbanti.
Aircraft used: F-22A
Special weapon: XSDB (Advanced Small Diameter Bomb)
Score required: 19,000
Time limit: First section 15:00 / second section 15:00 (Normal)
There are three areas where enemy activity is concentrated; the center, south-east and south-west. It's important not to waste any time to reach the score within the limit required.
First head to the central area straight in front of you and use your bombs (special weapon) to eliminate any ground vehicles. Once clear, move over to the south-eastern area and attack the aircraft, this can be tricky so take out a few for some points but don't linger too long. Next go to the south-westerly area over the sea and destroy as many boats / ships as possible - again with the bombs. After this I rearmed by heading due north to the return line. This also pauses the timer on the main mission while you land.
After rearming, I returned to the south-eastern area and shot down a few more planes. More ground enemies start spawning in along the coast so you can get a few more points but the defence also becomes a bit tougher.
The final part of this is a dog fight with several enemy aces which isn't terribly hard. I went for the wingmen first and left Mister X until last.Tip: I played through a couple of hours of multiplayer, gaining enough MRP (in game currency) to purchase the F-15E which made this a lot easier and more fun than the starting F-16C. Around Mission 12, I had enough to purchase the F-22A which is the most capable aircraft I've found so far. The currency, planes and most part upgrade unlocks work across multiplayer / singleplayer but some upgrades are exclusive to multiplayer. You can also go into 'Free Mission' to replay for some extra cash.