The Gunship is available on all Armoured Kill DLC maps:
Alborz Mountains (Flag C)
Death Valley (Flag C)
Bandar Desert (Flag E)
Armored Shield (Flag C)
You can control the Gunship in Rush or Conquest
. In Rush, you must be an attacker, and in Conquest you must control the flag that has the gunship icon near it.
You are able to spawn directly into the gunship, if it has available spots in it, and it allows for 2 people, but it is much easier being the main gunner. The gunship will fly around on its own, so don't worry about steering.
Spawning in the gunship is the hardest part, once inside, just switch to the largest shell, and aim at buildings, vehicles or choke points in the map. You can go to smaller shell if you have direct sight at infantry. Once you get the kill, you see "Player 1 [Gunship] Player 2" in the top corner, and the achievement will unlock.
Please view the below video for more info: