I did this Achievement on Mission 2. Start the level and spam your Rockets and missles at everything. Only kill the mission objectives and you'll be done in no time. There is a part where you have to shoot the machine gun while chasing the helicopter, and it Doesn't count against you. As soon as you exit the cockpit view DO NOT SHOOT THE MACHINE GUN, just continue with rockets. When you switch to the drone, continue shooting rockets and do not stop to fight in the cave. The Mini boss battle is easy if you hover low to the ground and stay behind the tank. He will never hit you if you keep popping your flares. Its a fairly short mission and very easy to beat.