The Northrop Grumman (formerly Ryan Aeronautical) RQ-4 Global Hawk (known as Tier II+ during development) is an unmanned aerial vehicle (UAV) used by the United States Air Force and Navy as a surveillance aircraft. In role and operational design, the Global Hawk is similar to the Lockheed U-2, the venerable 1950s spy plane. It is a theatre commander's asset to provide a broad overview and systematic target surveillance. For this purpose, the Global Hawk is able to provide high resolution Synthetic Aperture Radar (SAR) that can penetrate cloud-cover and sandstorms? and Electro-Optical/Infrared (EO/IR) imagery at long range with long loiter times over target areas. It can survey as much as 40,000 square miles (103,600 square kilometres) of terrain a day. It is used as a high-altitude platform for surveillance and security. Missions for the Global Hawk cover the spectrum of intelligence collection capability to support forces in worldwide military operations. According to the Air Force, the capabilities of the aircraft allow more precise targeting of weapons and better protection of forces through superior surveillance capabilities. The Global Hawk costs about US$35 million to procure each aircraft. With development costs included, the unit cost rises to US$218 million.