You did all the right things you first have to run to the river and destroy the guns on the wayout. Then go to the enemy base and make sure you blow up all the barrels. There is one in the open area, in partcially destroyed bulding, one behind the bunker behind the destroyed building, one upstairs in the ememy base and open on the side of the enemy base. Then it will say fuel supplies destroyed and then you go in the base and desrtoy all the computers. Make sure they are throughly destroyed.

umm it didnt work for me

first go to the water fall(the best way is to use the granade with soviet to destroy the two turret near the entrance to the water fall)then take the homing launcher and blow up the turret in the enemy base to make it easier.destroy the fuel drum on the up stair building,to the right of the building(outside),near the mountain(behind the buker),in an open area,and in the destroyed building(go through it and at the end of the building before the bunker to the right you will see a fuel drum).then, destroy a computer.(the easiest way is to destroy the computer with homing launcher first because after the fuel drum is destroy,you will not arrive in the water fall now and you need to go back to get a homing launcher and it took at least 6 second).