The patent describes a squad or platoon of perhaps 10 to 30 drones, able to follow targets or perch and observe like a fleet of mobile CCTV cameras. When a drone runs low on power it returns to the base station, which physically replaces the drone’s batteries. With no wait for recharging, the drone can fly off again at once. The autonomous battery-swapping device would “enable long, 24/7, uninterrupted missions,” says Vian. In principle, the base station would allow drones to operate in an area for days, weeks, or months at a stretch.