The key is to build your defenses, before going on the attack. Don't build the Airbase and Nanotech Mainframe until your defenses are established - you need the resources also to build units. Here's the detail... Build Tank Busters to garrison the nearest four buildings and keep replacing as needed. You will need resources from two Ore refineries in keeping pace with the attack, so expand your base east with two Instant Generators and two Wave-Force towers, then build a Ore refinery on the Ore mine. As fast as possible, send Wave-Force artillery tanks at the east to keep the enemy tanks at bay, in conjunction with the Wave-force towers. Build Defender VXs between the garrisoned buildings as an air attack will come soon. Add Wave-force towers, if you have surplus resources.