This achievement can be done on easy.
Both players must survive
Achievement should pop up right before you get into the car at the end of the level
-Use single shot and a combination of left trigger+right trigger. I do this all the time specially in dark areas where I can't see the enemies. Every time you press the left trigger, the game will auto aim to the nearest enemy. So remember single shot, left trigger quickly followed by a tap on the right trigger and watch those hit markers on your screen.
-Corner yourselves in a room, specially at the beginning and put claymores by the windows and door entrances.
-You start with the MP7, it's more than sufficient for the job. I use single shot and kill enemies easily
-The AEK-971 is also a superb weapon, again use single shot and kill enemies, I don't think silencers make a difference in the AI behavior so don't worry about it.
-For the parts where you get swarmed by enemies use your claymores again and have one guy right next to the ammo box and spamming grenades at the enemies. If one person stands next to the ammo box that person will have virtually infinite grenades.
-Watch out for the parts where you have to open doors as sometimes at enemy will be standing right behind. When you're asked to open a door, make sure your gun is on full-auto and get ready to spray anyone behind the door.
-There's a part near the end where there are some enemies standing behind a car, throw a grenade behind the car and make them go boom! Be careful though, just because the car blows up doesn't necessarily mean they're dead.
-Do NOT attempt to knife any enemies, this could back-fire and you might end up getting knifed.
-Stay away from shotguns. Now this might be my own personal taste but the shotguns in this level are automatic and take forever to reload, just stick to the MP7 or AEK-971. Again for the third time: Use single shot! This is the best way to shoot accurately and save ammo at the same time.
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