An aircraft or helicopter that is flown without an on-board human pilot. These vehicles are now customarily termed "unmanned aerial vehicles" (UAVs). Until the late twentieth century, they were typically called drones or sometimes remotely piloted vehicles (RPVs) when a human operator controlled the vehicle remotely. Although guided missiles and cruise missiles have the same root heritage in the "aerial torpedoes" of the 1910s, missiles are not considered to be UAVs. Crewless versions of nonpowered aerial vehicles such as gliders and balloons can perform some of the same missions as UAVs, but are not considered to be UAV-class vehicles.