Drone is a general term for an unmanned military vehicle, especially a flying one. Combat drones (or UCAVs) first apperared in the 1970s under USAF "HAVE LEMON" project. They promised reduced risk to the military personnel and costed much less than either manned aircraft and cruise missiles. At that time, though, they faced severe obstacles in the form of limited communication capability, problems with target recognition and resistance by conservative military officials. Next decades saw those problems overcome, and by 2010 US and Israeli armies routinely used drones for surveillance and strike missions. Those machines, although still supervised by human operators, were able to conduct their missions completely on their own, and so were the very first automatons which could challenge humans in actual combat.