Editing Northrop B-2 Spirit (section)

===Origins===
By the mid-1970s, military aircraft designers had learned of a new method to avoid missiles and interceptors, known today as "[[Stealth aircraft|stealth]]". The concept was to build an aircraft with an [[airframe]] that deflected or absorbed [[radar]] signals so that little was reflected back to the radar unit. An aircraft having radar stealth characteristics would be able to fly nearly undetected and could be attacked only by weapons and systems not relying on radar. Although other detection measures existed, such as human observation, [[Infrared search and track|infrared scanners]], and [[Acoustic location|acoustic locators]], their relatively short detection range or poorly developed technology allowed most aircraft to fly undetected, or at least untracked, especially at night.<ref>Rao, G.A. and S.P. Mahulikar. "Integrated review of stealth technology and its role in airpower". ''Aeronautical Journal'', v. 106 (1066), 2002, pp. 629–641.</ref>

In 1974, [[DARPA]] requested information from U.S. aviation firms about the largest [[radar cross-section]] of an aircraft that would remain effectively invisible to radars.<ref>Crickmore and Crickmore 2003, p. 9.</ref> Initially, [[Northrop Corporation|Northrop]] and [[McDonnell Douglas]] were selected for further development. [[Lockheed Corporation|Lockheed]] had experience in this field with the development of the [[Lockheed A-12]] and [[Lockheed SR-71 Blackbird|SR-71]], which included several stealthy features, notably its canted vertical stabilizers, the use of composite materials in key locations, and the overall surface finish in [[Radiation-absorbent material|radar-absorbing paint]]. A key improvement was the introduction of computer models used to predict the radar reflections from flat surfaces where collected data drove the design of a "faceted" aircraft. Development of the first such designs started in 1975 with the ''[[Lockheed Have Blue|Have Blue]]'', a model Lockheed built to test the concept.<ref>[http://www.centennialofflight.gov/essay/Evolution_of_Technology/Stealth_aircraft/Tech31.htm "Stealth Aircraft."] {{webarchive|url=https://web.archive.org/web/20110721035221/http://www.centennialofflight.gov/essay/Evolution_of_Technology/Stealth_aircraft/Tech31.htm |date=21 July 2011}} ''U.S. Centennial of Flight Commission'', 2003. Retrieved 5 November 2012.</ref>

Plans were well advanced by the summer of 1975, when [[DARPA]] started the Experimental Survivability Testbed project. Northrop and Lockheed were awarded contracts in the first round of testing. Lockheed received the sole award for the second test round in April 1976 leading to the ''Have Blue'' program and eventually the [[F-117]] stealth attack aircraft.<ref>{{harvnb|Griffin|Kinnu|2007|pp=14–15}}</ref> Northrop also had a classified technology demonstration aircraft, the [[Northrop Tacit Blue|Tacit Blue]] in development in 1979 at [[Area 51]]. It developed stealth technology, LO (low observables), [[fly-by-wire]], curved surfaces, composite materials, [[Signals intelligence|electronic intelligence]], and Battlefield Surveillance Aircraft Experimental. The stealth technology developed from the program was later incorporated into other operational aircraft designs, including the B-2 stealth bomber.<ref>''The integrator'', Northrop Grumman (newspaper), Vol. 8, No. 12; 30 June 2006, p. 8. author: Carol Ilten.</ref>