At the start of Trumpet's Sound, jump into the provided vehicle and follow the flags to the first overwatch position. Hop out and switch to your binoculars. They'll give you a better view at a far distance since your starting gun doesn't have a scope.
First, there are three tanks sitting across the way that will shell you if you get any closer than the overwatch position. You can take out two of them with a single artillery barrage if you're lucky, but you'll have to at least spend 2 on the tanks.
The first AT team is just down the hill from you and sometimes will move too close for you to really hit it with a barrage. Aim for their sandbags and either use a barrage or a loose spread. The second team is up the hill to your right, use another barrage or so to take them out. The final group is far to the left and you may have to move around to get a good line of sight on them. If you're having trouble with finding the teams, try taking out the tanks and then let your armor roll forward with the other humvees to take some of them out and let their shots give away enemy positions, then reload the checkpoint/mission.
After the area is cleared, you'll move up some more to an oil works area. There's plenty of explosives around but you should be safe. You'll have two extra squads that'll get on foot with you to assault is, so this'll be easier than most combat engagements. One enemy squad will come down the hill, while a second waits all the way on top. Clear your way to the top and across the way you'll see a few bunkers with more enemy troops. Your squad shouldn't have much trouble engaging at a distance, but if you want a scope, try grabbing a marksman rifle off of a dead Chinese soldier. Once the bunkers are clear you can move up towards them and across the street is another squad of AT gunners, take them out and the achievement will unlock provided that none of the three Abrams are destroyed. You may have to move quickly up and over the hill to beat them to the AT gunners.