Flo: If you haven't figured it out yet, here's the strategy that worked well for me. First, I made sure I had a heavy factory so I could build artillery, which is pretty much essential. With two artillery pieces deployed together near the initial reinforcement point (with a few tanks and soldiers for cover), I brought in as many other troops as I could, and took over the other two. I dropped another squad of artillery at the left point, where the bulk of my force was, and went around the north side.
With enough troops, the single light turret was easily defeated, and I could bring the artillery inside the shield. Once planted, I just kept my forces close and slowly steamrolled the base. Move the troops forward a bit, pack and then redeploy the artillery close enough to hit the next round of targets, and repeat as necessary. Once the shield is down, use your bombing runs and the artillery still at your start point to crush the rest of their base.