|Despite the achievement title, you just have to destroy 50 ground vehicles, not just tanks. The quickest way to do this is to do Co-op Campaign Mission 02. Equip yourself with one of the sniper rifles (preferably the M107.) When the mission starts, proceed left across the bridge, taking out as many enemies as you can with the sniper. Once you’ve eliminated most of the enemies in that area, you can use all of your grenades to blow up the various ground trucks/vehicles. You can also shoot vehicles to blow them up, too. Once you blow up all the vehicles in the area (approx. 5-6) you can quit out and restart mission and they’ll still count.|
Tip: Try getting your soldier’s Physical Training level to “Skilled” or higher, so they can carry an extra hand grenade.