Recon Expert Achievement
Online: unlock 3 weapons in the Recon kit
The recon class is the fourth class you can choose to spawn with. It includes a Sniper Rifle, motion sensor mines and C-4 explosives. To unlock more weapons in this class, you must get points with this as your spawned class. (Getting kills/destroying vehicles/destroying M-Com positions/etc).
You need 15,000 XP to unlock the third weapon for this achievement.