Cheap easy drones have a battery life of 15-25 minutes.And yet - where have I said anything untrue? If he's spent years studying these things he must be aware how easy it and cheap it is to make a drone, how these things can be used in swarms etc, how they can be autonomous and commanded remotely and fitted with payloads.
I would be ashamed if I spent years studying stuff and didn't know or take threats seriously.
More than 100 drones swarming a target could make things difficult.www.popularmechanics.com
Many countries and groups already use military drones, but Turkey is about to be the first to have a military drone armed with a machine gunwww.newscientist.com