The Cyber-Mole was a large vehicle used by the Cybermen to drill beneath London into the Earth's secret weapons store where the deadly doomsday bomb was being kept. They achieved this and held the world ransom with the bomb.
The Second Doctor brought his information on Cybermen to the military and lead an assault on the Cyber-Mole using anti-Cybermen weapons, defeating them. (TVC: Cyber-Mole)