Ace Combat: Assault Horizon

In the first/tutorial mission after Shooter1 talks about civilians, there are one moment where you go into DFM against one target plane and 3 others also appear on screen.

Although it is tempting to use the Special Weapon and kill all 4 at once, just shoot your target with a missile and you may go into DFM automatically with the next closest target. Thats an assault chain. Shoot down 3 planes this way and the achievement should pop up.

You cannot do when the tutorial prompts you to use the Special Weapon (the first time these planes fly in this "formation") as they are scripted to only die by those missiles.