http://www.civilization5.com/#/community/feature_gdrI'll let the Civilopedia do the talking:
The "Giant Death Robot" is a giant bipedal mechanical robot armed with a variety of missiles, Gatling gun arms, laser-beam eyes and a deadly kung-fu punch. Although not currently found in the modern battlefield, no doubt across the world governments and evil corporations are secretly developing these metal behemoths even as we speak. When these robots come into service, all of the world's other weaponry will become obsolete, and humanity's fate will be decided by a climactic battle between armies of good and evil Giant Death Robots in the streets of downtown Tokyo (assuming that the giant radioactive monsters don't get us first.)
How about some unit stats?
Combat Strength: 150
Movement: 3
Required Resource: Uranium
Required Tech: Nuclear Fusion
Penalty Attacking Cities
No Defensive Bonuses
Can Move After Attacking
Some guy requested it in 2004
http://forums.civfanatics.com/showthread.php?t=84982
