This article analyzes recent advances in unmanned aerial vehicle (UAV) technology and draws three conclusions. First, conventional military forces are highly vulnerable to armed UAVs. A small force of UAVs could decimate entire divisions of soldiers, armor, and artillery, eliminate the ability to resupply and sustain armies in the field, destroy all aircraft in a given theater, and put Nimitz-class carriers out of action. Second, urban population centers are highly vulnerable to UAVs controlled by terrorists. Third, enormous cost savings could be achieved by replacing highly vulnerable and expensive weapon systems with UAVs.