Project Zeus, also known as simply Zeus or the Zeus warheads was a cataclysmic weapon created by Cobra. These warheads were weapons which, when dropped from orbit over Earth, had the power to annihilate an entire city without any nuclear fallout.
Retaliation (2013 movie)
After assuming the role of the President of the United States, Zartan of Cobra invites the leaders of the world's nuclear nations to Fort Sumter with the stated goal of nuclear disarmament. When, however, they all balk at the idea, promising a 50% reduction at most, he tells them that anyone who does not surrender all of their nuclear weapons will be considered to be at war with the United States. He then launches America's arsenal, telling them that they are at all, forcing them to follow suit. As the world catapults towards nuclear catastrophe, he declares that they're on their own unless one of them cared to unilaterally disable their warheads, calling off his own nuclear assault.
In response, the heads of the other nations all abort and he declares "Welcome to a nuclear-free world." He then puts up images on a monitor, telling them that they are looking at their homelands and an advanced weapons system called Project Zeus. He continues that to direct a rod to their target, they don't launch it or fire it, they drop it from orbit and gravity does the rest. He demonstrates by having one of the rods dropped, obliterating the city of London, England. England's Prime Minister declares that he will have to answer for this, but then Cobra Commander takes over, saying that they will have to answer to him. He continues that the Cobra revolution has begun and that Zeus warheads are moving into position over the six remaining countries. He will stop them only for a price: total allegiance. Before he can continue, however, the G.I. Joe Team begins its assault to stop Cobra. In response, Firefly takes the case, intending to drop all of the remaining warheads. He is, however, intercepted by Roadblock, who manages to secure the case and end Cobra's assault.