Editing Lockheed YF-12 (section)

{{Short description|American prototype interceptor aircraft}}
{{Use American English|date=July 2019}}
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{{Use dmy dates|date=December 2019}}
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{{Infobox aircraft
 |name= YF-12
 |image= YF-12A.jpg
 |caption= YF-12A
 |type= [[Interceptor aircraft]]
 |manufacturer= [[Lockheed Corporation]]
 |designer= <!-- Only appropriate for one-person designers, not project leaders or chief designers -->
 |first_flight= 7 August 1963
 |introduction=
 |retired=
 |status= Canceled
 |primary_user= [[United States Air Force]]
 |more_users= [[NASA]]
 |produced=
 |number_built= 3
 |unit cost= US$15–18&nbsp;million (projected)<ref name=knaack/>
 |developed_from= [[Lockheed A-12]]
 |developed_into=
 |variants=
}}

The '''Lockheed YF-12''' is an American [[Mach number|Mach]]&nbsp;3+ capable, high-altitude [[interceptor aircraft|interceptor]] [[prototype]], developed and manufactured by American [[aerospace]] company [[Lockheed Corporation]].

The interceptor was developed during the late 1950s and early 1960s as a potential replacement for the [[F-106 Delta Dart]] interceptor for the [[United States Air Force]] (USAF). The YF-12 was a twin-seat version of the then-secret single-seat [[Lockheed A-12]] reconnaissance aircraft operated by the [[Central Intelligence Agency]] (CIA); unlike the A-12, it was furnished with the [[Hughes AN/ASG-18]] [[fire-control radar]] and could be armed with [[AIM-47 Falcon]] (GAR-9) [[air-to-air missile]]s. Its [[maiden flight]] was on 7 August 1963. Its existence was publicly revealed by President [[Lyndon B. Johnson]] on 24 February 1964; this move was to provide [[plausible deniability]] for the CIA-operated A-12 fleet, which closely resembled the prototype YF-12.<!--Relatedly, see also [[Lockheed SR-71 Blackbird#Designation as SR-71]], also discussing 1964 public disclosures of Blackbird family members.-->

During the 1960s, the YF-12 underwent flight evaluations by the USAF, but funding to put it into operational use was not forthcoming partly due to the pressing demands of the [[Vietnam War]] and other military priorities. It set and held speed and altitude world records of over {{convert|2000|mph|km/h}} and over {{convert|80000|ft|m}} (later surpassed by the closely related [[Lockheed SR-71 Blackbird|SR-71 Blackbird]]), and is the world's largest, heaviest and fastest crewed interceptor.<ref>{{cite book |url=https://books.google.com/books?id=YoNbTA--HRMC&pg=PA11 |title=X-Planes at Edwards |isbn=978-1-61060786-5 |page=11 |last=Pace |first=Steve |year=1995|publisher=Zenith Imprint }}</ref> Following its retirement by the USAF, it served as a research aircraft for [[NASA]] for a time, which used it to develop several significant improvements in control for future supersonic aircraft.