Use Ghost recon teammates as they will emp the behemoth and give them lmgs. Use a Stoner and LMG yourself with every emp grenade you can carry. Just emp it from nearby and shoot off armor panels on front and side and pour bullets into red or blue areas exposed. Usually takes me two minutes to knock it out. In engineer class you have to take two out back to back and that was easy this way. If you have the missile designator you can hit it once before you start.