To that end DARPA, the defence department’s advanced research projects agency, is running a programme called Gremlins, a name that also applies to the individual drones themselves. A Gremlin drone weighs 680kg and has a wingspan of nearly 3.5 metres. Once it has been dropped, deployed its wings and fired up its turbofan engine, it can fly to an area up to 500km away and in the words of Scott Wierzbanowski, the Gremlin programme’s head, “go in and create havoc”. That done, it would then return to its aerial mothership.