How to Obtain: Kill 2 enemy helicopters without getting hit in a Special Ops Survival game.
This could be one of those annoying achievements, but the video below shows you the best plan of action to take. During any Special Ops Survival game, you'll need to take down 2 helicopters without getting hit. Please note that being hit before your first attempt at shooting one down is okay. It's only after that you must be careful. There's multiple ways to do this but the most efficient and fastest way is by using a predator missile. One of the best maps to also do this on is "Carbon" due to its layout.
Helicopters spawn on wave 6 as well as ground units, so there are a few things you're going to need. First you'll need to save up around $7-10,000 (to be safe) before wave 6. Once wave 5 has ended, buy 2 sets of claymores then head to the Air Support Armory.
Once inside, purchase a predator missile. Before the wave starts, place your claymores around all the entry points, then wait for the helicopters to reach the map. When they do, simply fire your missile and hit the first one. Once it's down, purchase a 2nd missile with your remaining money and repeat. You must make sure NOTHING hits you after the first predator missile. If they do, you'll have to restart.
Another way is to buy two automatic weapons, and find a place where you can't be shot from above, then simply fire on one until you hear the minigun winding up, then retreat to cover, until it stops shooting, then repeat. Just as risky, but maybe easier to do without focusing on doing it.