Despite such caution, it is common to lose drones due to mechanical problems, disruption of command links and other problems.

FORBES: The Revolution In Unmanned Aircraft Is Overrated

When Mary Cummings, a former US Navy pilot, stopped flying F-18 fighter jets in 1997, there were no video links between cockpits and command centres, and even radio contact was patchy at times.

ECONOMIST: Robots go to war