The United States Air Force is almost finished testing a top-secret stealth drone at its Area 51 installation in Arizona, according to a report by Aviation Week.

The Northrup Grumman Corporation (NYSE:NOC)-built drone, named the RQ-180, will primarily be used for intelligence, surveillance and reconnaissance (ISR) missions and is seen as the direct replacement for the Lockheed Martin Corporation (NYSE:LMT) SR-71 “Blackbird,” which was retired in 1998.

The drone represents a shift from operations in combat zones back to the cold-war style operations where aircraft like the Blackbird would operate in contested or denied airspace without being seen.

The 15-ton drone, which can operate for 24 hours and up to 1,200 nautical miles from its base, has been funded by the Air Force’s classified budget and developed by Northup Grumman, which beat out competition from The Boeing Company (NYSE:BA) and Lockheed Martin.

The RQ-180 will benefit from an increased radar cross-section that will provide protection from low- and high-frequency threats from all directions, an improvement from Lockheed’s F-117, F-22 and F-35, which currently undertake some of the main duties that the drone will be expected to perform.

The new drone is similar in size to the non-stealthy RQ-4, currently serving in Iraq and Afghanistan but likely to be retired sometime next year.

In addition, the state-of-the-art design of the RQ-180 incorporates stealth with advanced aerodynamic efficiency for increased altitude, range and time on station, compared with its predecessor, the RQ-170, which can stay in the air for only five to six hours.