The Cybermen had hidden a bomb within a cave system on Earth, planning to detonate it to destroy the planet. While an expedition team was studying the caves, the androids were created to guard the hatch which held the bomb.
The androids made a distinctive whine and were not detectable by scanners. Their right hands had weapons embedded in them that could turn a human into a boiling puddle of molten flesh. They were fitted with monitoring so that the Cybermen could receive the images; the Cyber-Leader was also able to communicate with them. The androids were highly resistant to energy weapons and could only be destroyed by concentrated fire.
They were programmed both for survival and to strictly follow their programming. If they were damaged they wouldn't take unnecessary risks. However, a conflict between these two programmed instructions allowed the Fifth Doctor to confuse them by having Lieutenant Scott's men fire at the hatch (ie what they were programmed to protect). This confused the androids and allowed the soldiers to destroy them. (TV: Earthshock)
Behind the scenes Edit
The Cyber android costume were re-painted and used as the Raston Warrior Robot costume, which was ironically used to destroy multiple Cybermen.