Thunderground is a one-person tank combat game. You're behind enemy lines, and your mission is to take out the enemy bases by first eliminating their force fields and then shooting them with your atomic cannon. Sentry and digger tanks are poised and waiting to stop you.
You control a tank that can dig through the earth and create tunnels which you can use to attack the enemy bases. You can also dig away the force fields that are in front of the bases. Along the way, you will find special items, such as shovels, keys and flags, that will earn you extra points.
The enemy's sentry tanks can't create their own tunnels, so they're stuck driving through whatever you dig out. The digger tanks, however, have the same capabilities you have. You can shoot the enemy tanks, but if you destroy the second one, a new one will come out and take its place.
There is a timer of sorts along the bottom of the screen. You start your mission with six tanks. Three of them are displayed at a time and an enemy tank slowly moves toward them as you complete each round. It will destroy each of your extra tanks as it reaches them. Once you complete a round, it starts over again.
There are 12 levels and four rounds per level, each tougher than the last.