Killer drones have conquered the skies. Can we ever be safe again?

Consider a small military drone, electrically powered, commercially sourced, guided by GPS and a cellular link and the patience of whoever is holding the controller. The drone costs around $500. The missile sent to destroy it costs $2 million. This is, at the moment, the defining arithmetic of modern air defense, and the people responsible for solving it are very aware that they have not yet done so.

We have been in similar situations before. When the first aircraft appeared over battlefields in 1914, artillery was quickly tilted toward the sky. In World War II, barrage balloons forced attackers higher, degrading their accuracy, channeling them into envelopes where radar and gunfire could find them. Radar transformed air defense by making detection a network rather than a