The Rock Men are an alien race. They were once at war with another alien race known as the Crystal Men, and so they traveled to earth to use their weapon to destroy Mercury, the home world of the Crystal Men.
The Rock Men Army equip a drill-nosed craft which is capable of burrowing into the ground. Their enemies, the Crystal Men also use such technology in their own army. They also possess a weapon capable of beaming a signal into the core of Mercury that was capable of destroying the entire planet as well as the whole solar system.