Go up any of the ramps to the higher levels when fighting the big Tank at the end and hide behind one of the four shield generators. An intermission sequence will show the tank firing homing rockets at you but stay where you are. The tank will then fire lasers at you which can sometimes come through the walls. Reverse so that you are not hit and destroy the shield generator then move to the next shield
Generator when the lasers have finished and repeat the process. If you get badly damaged during this go to the garage and change vehicles. When ALL the shield sheild generators are down the tank can now be destroyed. Avoid getting too close to it or it will fire grenades at you. Use the plasma and run as soon as the tank says 'Preparing Homing Rockets', when the danger has cleared attack it again. Keep doing this until the tank is destroyed. This will probably take more than one attempt to do.