US Air Force 'secretly builds new stealth drone' It was developed for intelligence, surveillance and reconnaissance (ISR) missions, but "could also be capable of electronic attack missions," the magazine said. "It is similar in size and endurance to the Global Hawk," which can fly for 24 hours up to 1,200 nautical miles from its base. A first generation of unmanned aircraft, the non-stealthy Reapers and Global Hawks, were used in Afghanistan and Iraq, but they were deemed too vulnerable in enemy territory equipped with powerful anti-aircraft defences. Now the Air Force is slowly turning to stealth drones, better at passing safely over unfriendly territory. In December 2011, a spy drone that had until then been secret, the RQ-170 Sentinel, crashed inside Iranian air space. The unmanned craft, which had taken off from Afghanistan, was on a mission to observe Iran's nuclear sites for the CIA, according to US press reports. According to Aviation Week, the new RQ-180 "eclipses the smaller, less stealthy and shorter-range RQ-170 Sentinel."