Call of Duty

There is probably a better, faster, and guaranteed strategy in Mission 12 Gora Dam. I tested it over 20 times in my game, and it was working every time, so maybe if you follow my short steps, it will work for you too.

Load up Mission 12 Gora Dam on recruit difficulty, from the start parachute to the right side of the dam, and pick up the mortar strike. After this, defuse the two bombs nearby (car / inside) and start killing the enemies nearby. Then go on the right side to the staircase and start killing the enemies nearby.

At this point, you should get a radio message that reinforcements are coming with a helicopter, and this helicopter works for the achievement. Surprisingly, he stands completely still in the same position every time in the air when the reinforcements leave the chopper, perfect timing for a mortar strike ;)

PS: Sorry that there is no better explanation, but English is so damn hard as a non-speaker.

The best location i can find is during the mission 'Reactor'. Collect a mortar strike from the C3 grid on the map and then travel round destroying the mission objective. At some point an armored helicopter will spawn (I had issues on recruit getting it to spawn so recommend regular). Head over to D6 into the fire station and make your way to the top of the stairwell killing any approaching enemies and then into the next room. The helicopter will eventually lose track of you and will conveniently hover directly above the fire stattion. Place the mortar strike directly above you while still inside while under the helicopter. The arc of the mortar can be a little random and may not hit it first try, so either head over to H3 or C5 to acquire another, or reset the mission.

To note, i completed this task with a reinforcement helicopter and it did not count so stick with the armored helicopter.

Mission 3: Reactor

I've tried various methods and guides to get this working consistently. But this is the method I had the most success with, so sharing it as an achievement guide.

Helicopter #1 (North East):
As you initially parachute in head towards the large white hanger to the East with the letter "A" on the side. If you land directly in front of the letter "A" you'll find a supply drop with a Precision Airstrike. Pick up the airstrike and hustle over to the North East helicopter in H4, use the Precision Airstrike on it.

Helicopter #2 (South East):
Next grab the Cruise Missile found in square F4 and use the Cruise Missile to take out the South East helicopter in G7.

Helicopter #3 (West):
At this point the armoured helicopter should now be patrolling the skies, ignore him for now. Make your way to the Mortar Strike in square C5, collect the Mortar Strike from the rooftop. While still on the roof, destroy the last objective helicopter in D4 with the Mortar Strike. This will create a perfect checkpoint on that very rooftop, which we'll use to destroy the armoured helicopter.

Armoured Helicopter:
Now with a checkpoint on that rooftop, press and restart checkpoint. This will reset the armoured helicopter, making it non-hostile and stationary somewhere in the middle of the map. Quickly run over and grab the Mortar Strike before the armoured helicopter spots you. Then run in the opposite direction from the armoured helicopter to stay out of combat. Now use the Mortar Strike on the armoured helicopter at range to destroy it. I found the tower in square B6 was a great spot to stand as the mortar would hit 9 times out of 10.

Credit to Macca for the guide -- figured I'd throw in a video demonstrating his method

Load into "Reactor" and take out one or two of the helicopters - enough for the attack helicopter to spawn.

Go back to the first building just short of the first helicopter. On the roof will be a Mortar Strike.

From there, fly to the right of the helicopter to the fire station and clear out the building of enemies until the mini-map turns yellow.

From there, target the mortar strike at the ground while in the fire station and fire it.

Eventually one of the mortars will take out the attack helicopter and the achievement should pop!

If it doesn't, reload the mission and try again as the mortar strike is not 100% accurate.

Shoutout to Lordmacca666 on TrueAchievement for the guide

MW3 - That's One Way to Do It...
Destroy an airborne enemy helicopter with a Mortar Strike

Mission Reactor
From the start of the mission quickly grab a Mortar Strike Armament from around the C5 or H3 grid. Next destroy the first objective any way you want to (other then using the mortar strike) after this you can try to get the achievement with the reinforcement helicopter, however I could not get that to work right. So I recommend destroying the second objective, now depending on how fast you are an attack helicopter will spawn this is the one you want to hit with the mortar strike. Now I found the best way for me at least was to agro the helicopter and wait for it to move to a new location & start shooting at me. If you follow the video below I show exactly what you need to do. Hopefully you enjoy the video.