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{{Short description|U.S. Air Force stealth air superiority fighter program}}
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{{Infobox aircraft
  |name= Advanced Tactical Fighter (ATF)
  |image= YF-22 and YF-23.jpg
  |caption= The YF-22 (foreground) and YF-23 (background)
  |aim= [[Air superiority fighter]]
  |requirement=Advanced Tactical Fighter Statement of Operational Need (November 1984), System Operational Requirements Document (December 1987)
  |issuer= United States Air Force
  |service=
  |value= $US 86.6 billion when winner was selected<ref name=GS>Pike, John. [http://www.globalsecurity.org/military/systems/aircraft/f-22-history.htm "History of the F-22 program"]. Globalsecurity.org, 21 January 2008.</ref>
  |initiated={{Start date|1981|05}} (RFI), {{Start date|1985|09}} (RFP)
  |proposals= proposals from [[Boeing]], [[General Dynamics]], [[Grumman]], [[Lockheed Corporation|Lockheed]], [[Northrop Corporation|Northrop]], [[McDonnell Douglas]], and [[Rockwell International|North American Rockwell]]<ref name=Miller_p14-9>Miller 2005, pp. 14, 19.</ref>
  |prototypes= [[Lockheed YF-22]], [[Northrop YF-23]]
  |concluded= {{End date|1991|08}}
  |outcome= Lockheed team selected for full-scale development of the [[Lockheed Martin F-22 Raptor|F-22]] for production and service
  |predecessors=
  |successors=
  |related= JAFE/ATFE, NATF, [[Have Dash II]]
}}

The '''Advanced Tactical Fighter''' ('''ATF''') was a program undertaken by the [[United States Air Force]] to develop a next-generation [[air superiority fighter]] to replace the [[McDonnell Douglas F-15 Eagle|F-15 Eagle]]. The proposed fighter was intended to counter emerging worldwide threats in the 1980s, including Soviet [[Sukhoi Su-27]] and [[Mikoyan MiG-29]] fighters under development, [[Beriev A-50]] airborne warning and control systems (AWACS), and increasingly sophisticated [[surface-to-air missile]] systems.

The ATF would make a leap in performance and capability by taking advantage of emerging technologies, including advanced avionics and flight control systems, more powerful propulsion systems, and stealth technology. [[Lockheed Corporation|Lockheed]] and [[Northrop Corporation|Northrop]] were selected in 1986 as finalists for the program's Demonstration and Validation (Dem/Val) phase. They would be the lead contractors to respectively develop the [[Lockheed YF-22|YF-22]] and [[Northrop YF-23|YF-23]] technology demonstrator prototypes, the associated avionics prototypes, and the system specification; the prototype aircraft were flight tested in 1990.

After evaluations, the Lockheed team was selected in 1991 for ATF full-scale development, or [[Manufacturing readiness level#Definitions|Engineering and Manufacturing Development]] (EMD). The Lockheed team developed their design into the [[Lockheed Martin F-22 Raptor|F-22 Raptor]], which first flew in 1997, for production and operational service; a naval version of the ATF (called NATF) was considered as an [[Grumman F-14 Tomcat|F-14 Tomcat]] replacement but was later canceled due to costs.

==Background==
{{multiple image
 | align = left
 | total_width = 300
 | footer = Emerging Soviet threats such as [[Mikoyan MiG-29|MiG-29 "Fulcrum"]] (left) and [[Sukhoi Su-27|Su-27 "Flanker"]] (right) would spur the development of the Advanced Tactical Fighter
 | image1 = MiG-29 fuselage.jpg
 | alt1 = MiG-29 "Fulcrum"
 | caption1 =
 | image2 = Su-27 05.jpg
 | alt2 = Su-27 "Flanker"
 | caption2 = 
}}

Although the term "Advanced Tactical Fighter" (ATF) appeared in U.S. Air Force (USAF) parlance as far back as 1971 to describe potential future tactical aircraft, the program that would eventually result in the F-22 began in 1981.<ref>Aronstein and Hirschberg 1998, p. 5.</ref> This was motivated by the shift in U.S. military doctrine towards striking the enemy's rear echelon as eventually outlined in the [[AirLand Battle]] concept, as well as intelligence reports of multiple emerging worldwide threats emanating from the [[Soviet Union]]. Between 1977 and 1979, American satellite photographs of the "''Ram-K''" and "''Ram-L''" fighter prototypes at [[Gromov Flight Research Institute|Ramenskoye air base]] in Zhukovsky—later identified as the [[Sukhoi Su-27|Su-27 "Flanker"]] and the [[Mikoyan MiG-29|MiG-29 "Fulcrum"]] respectively—indicated that a new generation of Soviet fighter aircraft comparable to the recently introduced [[McDonnell Douglas F-15 Eagle|F-15 Eagle]] and [[General Dynamics F-16 Fighting Falcon|F-16 Fighting Falcon]] would soon enter service.<ref>Aronstein and Hirschberg 1998, pp. 17–18.</ref>

Also concerning were Soviet reports of "[[look-down/shoot-down]]" capability being introduced on an advanced [[Mikoyan-Gurevich MiG-25|MiG-25]] derivative, later revealed to be the [[Mikoyan MiG-31|MiG-31 "Foxhound"]], as well as the appearance of an [[Ilyushin Il-76|Il-76]]-based [[airborne warning and control system]] (AWACS) aircraft called the [[Beriev A-50|A-50 "Mainstay"]]. These systems, revealed in 1978, greatly reduced the effectiveness and survivability of [[nap-of-the-earth|low-altitude penetration]]. Furthermore, experience and data from the [[Vietnam War]] and the more recent [[Yom Kippur War|1973 Arab-Israeli war]] demonstrated the increasing lethality and sophistication of Soviet surface-to-air missile systems.<ref>Aronstein and Hirschberg 1998, p. 12.</ref><ref>Metz 2017, pp. 8–10.</ref><ref>Miller 2005, pp. 10–11.</ref>

==Program history==
===Concept development===
[[File:F-22 RFI.jpg|thumb|upright=1.25|Diagram of several designs submitted for request for information (RFI)]]
In 1981, the USAF began forming requirements for the ATF, eventually codenamed "''Senior Sky''". In May, a [[request for information]] (RFI) to the aerospace industry was published by the USAF [[Aeronautical Systems Center|Aeronautical Systems Division]] (ASD), followed by another RFI for the ATF propulsion systems in June. In response, a number of aerospace [[defense contractor]]s provided design concepts for analysis by the ASD, which released their final report in December 1982.<ref>Aronstein and Hirschberg 1998, pp. 30-33.</ref> During this time, the ASD also established an internal ATF Concept Development Team (CDT) in October 1982 to manage concept development studies. As the ATF was still early in its requirements definition, including whether the aircraft should be focused on air-to-air or air-to-surface, there was great variety in the RFI responses; the submitted designs generally fell into four concepts.<ref name="ReferenceA">Aronstein and Hirschberg 1998, p. 40.</ref>

* ''Numbers Fighter'' (N): Lightweight, low-cost design trading lower individual capability for quantity.
* ''Supersonic Cruise and Maneuver'' (SCM): Approximately {{convert|55000|lb|kg|abbr=on|adj=on|sigfig=3}} takeoff weight fighter with high maneuverability and [[Energy–maneuverability theory|specific excess power]] at transonic and supersonic speeds.
* ''Subsonic Low Observable'' (SLO): An internal ASD concept that sacrificed fighter-like performance and speed for low [[radar cross-section]] and [[infrared signature]].{{refn|Despite the conceptual similarities, the SLO (based on a General Dynamics flying wing design) was separate from the ''"Senior Trend"''/[[Lockheed F-117 Nighthawk|F-117]] due to the latter's classification and special access restriction as a "black" program.<ref name="ReferenceA">Aronstein and Hirschberg 1998, p. 40.</ref>|group=N}}
* ''High-Mach/High-Altitude'' (HI): Large and fast missileer aircraft over {{convert|100000|lb|kg|abbr=on|sigfig=3}} at takeoff intended to operate well above Mach 2 and {{convert|50000|ft|m|sigfig=3}}.

Further analysis by ASD would indicate that the best air-to-surface concept was ''SLO'', while the best air-to-air concept was ''SCM''; neither ''N'' nor ''HI'' were rated highly, and responses from contractors also broadly agreed on avoiding either extremes of the quality-versus-quantity spectrum. Even with the variety of the submitted designs in the responses, the common areas among some or all the concepts were reduced observability, or [[stealth technology|stealth]] (though not to the extent of the final requirements), short takeoff and landing ([[STOL]]) and sustained supersonic cruise without afterburners, or [[supercruise]].<ref name=Sweetman_p12>Sweetman 1991, pp. 12–13.</ref><ref name="A&H1998p42-45">Aronstein and Hirschberg 1998, pp. 42-45.</ref>  It was envisioned that the ATF would incorporate emerging technologies to include advanced alloys and [[composite material]], advanced avionics and [[fly-by-wire]] flight control systems, higher power propulsion systems, and low-observable, or stealth technology.<ref name=Sweetman_p10-1>Sweetman 1991, p. 10-11, 21.</ref><ref name="Hehs1998P1">Hehs 1998, Part 1.</ref>

[[File:Advanced Tactical Fighter Systems Project Office Patch.jpg|thumb|left|ATF SPO Patch, 1990]]
By October 1983, the ATF Concept Development Team had become the System Program Office (SPO) led by Colonel Albert C. Piccirillo at [[Wright-Patterson Air Force Base]].<ref name="A&H1998p56-57">Aronstein and Hirschberg 1998, pp. 56-57.</ref> After discussions with [[Tactical Air Command]] (TAC), the CDT/SPO determined that the ATF should focus on air-to-air missions. The air-to-surface missions would be handled by the upgraded [[General Dynamics F-111 Aardvark|F-111]], the upcoming [[Enhanced Tactical Fighter|Dual-Role Fighter]] (DRF) (which would result in the [[F-15E Strike Eagle]]) as well as the then-classified [[Lockheed F-117 Nighthawk|F-117 Nighthawk]] ("''Senior Trend''"), while the air-to-air threat from the new Soviet fighters and AWACS remained.{{refn|Early on, the F-117 had been considered for hunting the Soviet AWACS, but this was deemed not effective in 1982.<ref>Aronstein and Hirschberg 1998, p. 50.</ref>|group=N}} Additionally, as with ASD and industry responses, TAC did not want the ATF to be at either extremes of the quality-versus-quantity spectrum.<ref name=Miller_p13/><ref name="A&H1998p45-54"/> The ATF would thus be a new air superiority fighter in the vein of the SCM concept with outstanding aerodynamic performance, and intended to replace the capability of the [[McDonnell Douglas F-15 Eagle|F-15 Eagle]]. In the potential scenario of a Soviet and [[Warsaw Pact]] invasion in [[Central Europe]], the ATF was envisaged to launch from bases in central England and support the [[AirLand Battle|air-land battle]] by performing [[offensive counter air|offensive]] and defensive counter-air missions against the Soviet air-to-air threats. This would then allow the DRF and other strike aircraft to perform [[air interdiction]] against ground targets.<ref name="A&H1998p45-54">Aronstein and Hirschberg 1998, pp. 45-54, 72.</ref><ref>{{cite magazine |last=Canan |first=James |date=1 April 1988 |title=Sorting Out the AirLand Partnership |url=https://www.airandspaceforces.com/article/0488airland/ |magazine=Air Force Magazine |location=Colorado Springs, Colorado |publisher=Air Forces Association |access-date=}}</ref>

With the ATF's mission now focused on air-to-air, another round of requests were sent to the industry for concept exploration and study contracts were awarded to seven airframe manufacturers for further definition of their designs.<ref name="A&H1998p56-57"/> A request for proposals (RFP) for the fighter's engine, initially called the Joint Advanced Fighter Engine (JAFE) due to its potential joint application with the U.S. Navy's short-lived Advanced Carrier-Based Multirole Fighter (VFMX), was released in May 1983 to [[Allison Engine Company|Allison]], [[General Electric]], and [[Pratt & Whitney]]. In September 1983, General Electric and Pratt & Whitney each received $202 million contracts (~${{Format price|{{Inflation|index=US-GDP|value=202000000|start_year=1983}}}} in {{Inflation/year|US-GDP}}) for the development and production of prototype engines; Allison chose to not submit a bid due to technical problems with their advanced development demonstrators.<ref name=Sweetman_p13>Sweetman 1991, p. 13.</ref><ref>Aronstein and Hirschberg 1998, pp. 207-208.</ref> The SPO also expected that avionics would be a major component of the ATF in light of rapidly advancing semiconductor technology; requests for advanced avionics components such as the integrated [[electronic warfare]] system were sent out that November.<ref name="ReferenceB">Aronstein and Hirschberg 1998, p. 61.</ref>

During this time, the SPO took an increasing interest in stealth as results from classified [[Special access program|special access]] or "[[black project|black world]]" programs such as the [[Lockheed Have Blue|''Have Blue'']]/F-117, [[Northrop Tacit Blue|''Tacit Blue'']], and the Advanced Technology Bomber (ATB) program (which would result in the [[Northrop Grumman B-2 Spirit|B-2 Spirit]], or "''Senior Ice''") promised greatly reduced radar cross sections (RCS) that were orders of magnitude smaller than existing aircraft.{{refn|The [[Radar#Radar range equation|radar range equation]] meant that all else being equal, detection range is proportional to the fourth root of RCS; thus, reducing detection range by a factor of 10 requires a reduction of RCS by a factor of 10,000.<ref>Aronstein and Hirschberg 1998, p. 270.</ref>|group=N}}<ref name="A&H1998p56-57"/><ref name="Hehs1998P1"/> The ATF requirements would place increasing emphasis on stealth to improve survivability over the course of concept exploration, while still demanding fighter-like speed and maneuverability; the combination of low observables with the SCM concept was expected to greatly reduce the lethal zone of hostile surface-to-air missiles.<ref name="A&H1998p42-45"/> As a result of stealth technology, the design details became "black" even though the ATF was a publicly acknowledged program. By late 1984, the SPO had settled on the ATF requirements and released the Statement of Operational Need (SON). The SON called for a fighter with a takeoff gross weight of {{convert|50000|lb|kg|sigfig=2}}, a [[radius of action|mission radius]] of {{convert|500|nmi|mi km|sigfig=2}} mixed subsonic/supersonic or {{convert|700|-|800|nmi|mi km|sigfig=3}} subsonic, supercruise speed of Mach 1.4–1.5, the ability to use a {{convert|2000|ft|m|sigfig=1|adj=on}} runway, and signature reduction particularly in the frontal sector.<ref name=Miller_p13>Miller 2005, p. 13.</ref><ref>Aronstein and Hirschberg, pp. 105-106, 209.</ref>

===Request for proposals===
The [[request for proposals]] (RFP) for demonstration and validation (Dem/Val) was issued in September 1985, with proposals initially to be due that December.<ref name="USAF museum">{{cite web |url=http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2382 |title=YF-22 fact sheet |publisher=National Museum of the U.S. Air Force |archive-url=https://web.archive.org/web/20120119223134/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2382 |archive-date=January 19, 2012}}</ref><ref name=Sweetman_p14>Sweetman 1991, p. 14.</ref> The top four proposals, later reduced to two to reduce program costs, would proceed with Dem/Val. The RFP not only had the ATF's demanding technical requirements, but also placed great importance on [[systems engineering]], technology development plans, and risk mitigation; in fact, these areas were deemed more important than the aircraft designs themselves as contractors would later discover in their debriefs after Dem/Val selection.<ref name="Hehs1998P2"/><ref>Mullin 2019.</ref> This was because the SPO anticipated that the ATF would need to employ emerging technologies beyond even the contemporary state-of-the-art and did not want a point aircraft design frozen at then-mature [[technology readiness level]]s; as such, the SPO needed to evaluate its confidence in a contractor's ability to effectively and affordably develop new technology. Initially, there was no requirement for flying prototype air vehicles.<ref name="A&Hp82-89"/>

At this time, the SPO had anticipated procuring 750 ATFs at a unit cost of $35 million in fiscal year (FY) 1985 dollars (~${{Format price|{{Inflation|index=US-GDP|value=35000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}) with final design selection in 1989 and service entry in 1995 with a peak production rate of 72 aircraft per year. However, even at this point, the peak rate was being questioned and the entry date was at risk of slipping to the late 1990s due to potential RFP adjustments and budget constraints.<ref name="A&Hp82-89"/> Shortly afterwards, the Navy under Congressional pressure joined the ATF program initially as an observer to examine the possibility of using a navalized derivative of the ATF by adapting the design for [[CATOBAR|carrier operations]]; named the Navy Advanced Tactical Fighter (NATF), it was to replace the [[Grumman F-14 Tomcat|F-14 Tomcat]]. The Navy would eventually announced in 1988 that they would procure 546 aircraft under the NATF program at a peak rate of 48 per year.<ref name=Miller_p14>Miller 2005, p. 14.</ref><ref name="A&H1998p235-239">Aronstein and Hirschberg 1998, pp. 235-239.</ref>

The Dem/Val RFP would indeed see some changes after its first release that pushed the due date to July 1986; in December 1985, following discussions with Lockheed and Northrop, the two contractor teams with prior stealth experience from the ''Have Blue''/F-117 and ATB/B-2 respectively, all-aspect stealth requirements were drastically increased. Furthermore, the [[Packard Commission]], a federal commission by President [[Ronald Reagan]] to study [[Department of Defense]] procurement practices, had released its report in February 1986 and one of its recommendations was a "fly-before-buy" competitive procurement strategy that encouraged prototyping. The ATF SPO was pressured to follow the recommendations of the Packard Commission, and in May 1986, the RFP was changed so that final selections would involve flying prototypes.<ref name="Mullin2012p18-21"/> Because of this late addition due to political pressure, the prototype air vehicles were to be "best-effort" machines not meant to perform a competitive flyoff or represent a production aircraft that meets every requirement, but to demonstrate the viability of its concept and mitigate risk. The increased costs associated with aircraft prototyping was also partly why the number of Dem/Val finalists was reduced from four to two.{{refn|group=N|The JAFE program, later renamed the ATF Engine (ATFE) program, were modified around this time as well to provide flightworthy examples for the prototypes, and the SPO would assume management of the ATF engine effort in February 1987.<ref>Aronstein and Hirschberg 1998, pp. 208, 215-217.</ref>}}<ref name="A&Hp82-89">Aronstein and Hirschberg 1998, pp. 82-89.</ref><ref name="ATF_chief_eng"/>

[[File:Lockheed Model 090P 300x172.jpg|thumb|left|Lockheed's submission for Dem/Val RFP. The eventual YF-22 would have a completely different configuration.]]
In July 1986, proposals were provided by [[Boeing]], [[General Dynamics]], [[Grumman]], Lockheed, Northrop, [[McDonnell Douglas]], and [[Rockwell International|North American Rockwell]]; Grumman and North American Rockwell would drop out shortly afterwards.<ref name=Miller_p14-9/> Because contractors were expected to make immense investments of their own — likely approaching the amount awarded by the contracts themselves when combined — in order to develop the necessary technology to meet the ambitious requirements, teaming was encouraged by the SPO. Following proposal submissions, Lockheed (through its [[Skunk Works]] division), Boeing, and General Dynamics formed a team to develop whichever of their proposed designs was selected, if any. Northrop and McDonnell Douglas formed a team with a similar agreement.<ref>Goodall 1992, p. 94.</ref><ref name="A&H1998p164"/>

[[File:Northrop ATF DP110 300x258.jpg|thumb|Northrop's submission for Dem/Val RFP. In contrast to Lockheed, note the great similarity to the eventual YF-23.]]
On 31 October 1986, Lockheed and Northrop, the two industry leaders in [[stealth aircraft]], were selected as first and second place respectively and would proceed as the finalists. Noteworthy is the divergent approach of the two finalists' proposals. Northrop's proposal leveraged its considerable experience with stealth to produce a refined and well-understood aircraft design that was very similar to the eventual flying prototype.<ref name="Chong2016p237-238">Chong 2016, pp. 237-238.</ref><ref name="Metz2017p25-27">Metz 2017, pp. 25-27.</ref> While Lockheed also had extensive prior stealth experience, their actual aircraft design was quite immature and only existed as a rough concept that would have to be extensively redesigned; instead, Lockheed primarily focused on systems engineering and [[trade study|trade studies]] in its proposal, which pulled it ahead of Northrop's to take top ranking.<ref name="Mullin2012p18-21">Mullin 2012, pp. 18-21.</ref><ref name="Hehs1998P2">Hehs 1998, Part 2.</ref> The two teams, Lockheed/Boeing/General Dynamics and Northrop/McDonnell Douglas, were awarded $691 million [[fixed-price contract#Firm Fixed Price Contract (FFP)|firm fixed-price contract]]s in FY 1985 dollars (~${{Format price|{{Inflation|index=US-GDP|value=691000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}) and would undertake a 50-month Dem/Val phase, culminating in the flight test of two technology demonstrator prototypes, the [[Lockheed YF-22|YF-22]] and the [[Northrop YF-23|YF-23]]. Pratt & Whitney and General Electric would also receive $341 million (~${{Format price|{{Inflation|index=US-GDP|value=341000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}) each for the development and prototyping of the competing engines (designated YF119 and YF120 respectively), and the JAFE propulsion effort would later be renamed ATF Engine (ATFE) and directly managed by the ATF SPO.<ref name=Miller_p19-0>Miller 2005, pp. 19–20.</ref><ref name="A&H1998p164"/>

===Demonstration and validation===
{{main|Lockheed YF-22|Northrop YF-23}}
The Dem/Val phase was intended to develop and mature ATF technologies that would facilitate the fighter's eventual full-scale development and production, and focused on three main activities: requirements and [[requirements engineering|system specification development]], [[avionics]] ground prototypes and flying laboratories, and prototype air vehicles.<ref name="A&Hp104">Aronstein and Hirschberg 1998, p. 104.</ref> During Dem/Val, the ATF SPO program manager was Colonel James A. Fain, while the technical director (or chief engineer) was Eric "Rick" Abell. The director of ATF requirements was Colonel David J. McCloud of TAC, and the draft System Operational Requirements Document (SORD), derived from the 1984 SON, was released in December 1987.<ref>Aronstein and Hirschberg 1998, p. 106.</ref> In addition to the government contract awards, company investments during Dem/Val would amount to $675 million and $650 million (~${{Format price|{{Inflation|index=US-GDP|value=675000000|start_year=1988}}}} and ~${{Format price|{{Inflation|index=US-GDP|value=650000000|start_year=1988}}}} in {{Inflation/year|US-GDP}}) for the Lockheed and Northrop teams respectively, not counting additional investments during prior phases or by subcontractors. Pratt & Whitney and General Electric would each invest $100 million as well (~${{Format price|{{Inflation|index=US-GDP|value=100000000|start_year=1988}}}} in {{Inflation/year|US-GDP}}).<ref name="A&H1998p164">Aronstein and Hirschberg 1998, p. 164.</ref>

With the ATF system specification, the SPO had set the technical requirements without specifying the "how"; this was meant to give the contractor teams flexibility in developing the requisite technologies and offer competing methods.<ref name="A&Hp104"/> Furthermore, the SPO was also open to adjusting requirements if necessary. Both the Lockheed and Northrop teams conducted performance and cost trade studies and presented them in system requirement reviews (SRRs) with the SPO periodically during Dem/Val. This enabled the SPO to adjust ATF requirements and delete those that were significant weight and cost drivers while having marginal operational value. For instance, the number of internal missiles (represented by the [[AIM-120 AMRAAM|AIM-120A]]) was reduced from eight to six to reduce weight and cost.{{refn|A clipped-fin variant of the AMRAAM, the AIM-120C, was eventually developed to increase the F-22's internal missile load back to eight.<ref>Aronstein and Hirschberg 1998, p. 60.</ref>|group=N}}<ref name="Hehs1998P2"/> Because of the added weight for thrust vectoring/reversing nozzles and related systems on the [[McDonnell Douglas F-15 STOL/MTD|F-15 STOL/MTD]] research aircraft, the SPO changed the runway length requirement to {{convert|3000|ft|m|sigfig=1}} and removed the thrust reverser requirement in late 1987.<ref name=Sweetman_p23>Sweetman 1991, p. 23.</ref><ref name=Miller_p23>Miller 2005, p. 23.</ref> The [[ejection seat]] requirement was downgraded from a fresh design to the existing McDonnell Douglas [[ACES II]]. However, both contractor teams still found the {{cvt|50000|lb|kg|-2}} takeoff gross weight goal unachievable, so this was increased to {{cvt|60000|lb|kg|-2}}, resulting in engine thrust requirement increasing from {{cvt|30000|lbf|kN|0}} class to {{cvt|35000|lbf|kN|0}} class. Furthermore, Dem/Val would be extended several times to better mature technologies and reduce near-term budgets.<ref name="A&Hp105-108">Aronstein and Hirschberg 1998, pp. 105–108.</ref>

[[File:Boeing 757 Prototype N757A F-22 Raptor Systems Testbed.jpg|thumb|left|The [[Boeing 757]] used for testing the Lockheed team's avionics and later modified into the Flying Test Bed during full-scale development.]]
Aside from advances in air vehicle and propulsion technology, the ATF would make a leap in terms of avionics performance with a fully integrated avionics suite that [[sensor fusion|fuses sensor information]] together into a common tactical picture, thus improving the pilot's situational awareness and reducing workload; the avionics were expected to make up about 40% of the ATF's flyaway cost. The avionics system was to employ the ''[[PAVE|PAVE PILLAR]]'' system architecture and leverage technology from the [[Very High Speed Integrated Circuit Program|Very High Speed Integrated Circuit]] program; software would primarily be written in [[Ada (programming language)|Ada]].<ref name="ReferenceB"/>{{refn|The ATF/PAVE PILLAR architecture was the basis for the Joint Integrated Avionics Working Group (JIAWG) formed in 1986, which was to develop a common avionics architecture for the ATF, Advanced Light Helicopter (LHX), and Advanced Tactical Aircraft (ATA) programs; the latter two programs, resulting in the [[Boeing-Sikorsky RAH-66 Comanche|RAH-66 Comanche]] and the [[McDonnell Douglas A-12 Avenger II|A-12 Avenger II]] respectively, would eventually be canceled.<ref>Aronstein and Hirschberg 1998, pp. 173-175</ref>|group=N}} The Dem/Val phase for avionics development was marked by demonstrations of the hardware and software with Avionics Ground Prototypes (AGP) to evaluate performance and reliability. The SPO gave the teams flexibility to pick their own vendors for some subsystems; for instance, the Lockheed team's [[infrared search and track]] (IRST) sensor was supplied by General Electric, while Northrop team's was from [[Martin Marietta]]; both teams chose the [[Westinghouse Electronic Systems|Westinghouse]]/[[Texas Instruments]] [[active electronically scanned array]] (AESA) radar.{{refn|group=N|The Westinghouse/Texas Instruments radar design would beat the Hughes/General Electric design and became the [[AN/APG-77]].<ref name="A&H1998p181">Aronstein and Hirschberg 1998, p. 181.</ref>}} The integrated electronics warfare and integrated communication, navigation, and identification avionics were selected by the SPO.<ref name="A&H1998p181"/> Although not required, both teams would employ flying avionics laboratories as well, with the Lockheed team using a modified [[Boeing 757]] and the Northrop team using a modified [[BAC One-Eleven]].<ref>Aronstein and Hirschberg 1998, pp. 113-115.</ref> The avionics requirements were also the subject of SRRs and adjustments; as avionics was a significant cost driver, [[side looking airborne radar|side-looking radar]]s were deleted, and the dedicated IRST system was downgraded from multicolor to single color before changing from requirement to goal and provision for future addition.<ref name="A&Hp105-108"/> In 1989, a $9 million per aircraft cost cap on avionics in FY 1985 dollars (~${{Format price|{{Inflation|index=US-GDP|value=9000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}) was imposed by the SPO to contain requirements creep.<ref name="Hehs1998P2"/><ref>Mullin 2012, p. 36.</ref>

Finally, two examples of each prototype air vehicles were built and flown for Dem/Val: one with [[General Electric YF120]] engines, the other with [[Pratt & Whitney F119|Pratt & Whitney YF119]] engines.<ref name="USAF museum" /><ref>{{cite web |url=http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2383 |title=YF-23 fact sheet |publisher=National Museum of the U.S. Air Force |archive-url=https://web.archive.org/web/20110716073256/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2383 |archive-date=July 16, 2011}}</ref> Contractor teams made extensive use of analytical and empirical methods for their air vehicle designs, including [[wind tunnel]] testing, RCS pole testing, and software for [[computational fluid dynamics]], RCS calculations, and [[computer-aided design]].{{refn|group=N|For example, the Lockheed team conducted 18,000 hours of wind tunnel testing during Dem/Val.<ref>Aronstein and Hirschberg 1998, pp. 121-125.</ref>}} Consistent with the SPO's willingness to give contractor teams the flexibility in determining how to achieve the ATF requirements, the flight test plans were created and executed by the teams themselves and the prototype air vehicles were not flown against each other for direct comparisons; neither the YF-22 nor YF-23 would share the same test points, which were set by their own teams to [[technology demonstration|demonstrate concept viability]] and validate engineering predictions.{{refn|group=N|The contractor teams were to give the SPO "sealed envelope" flight performance predictions against which their aircraft would be evaluated, rather than against each other.<ref name="A&Hp82-89"/>}}<ref>Aronstein and Hirschberg 1998, p. 137.</ref> Noteworthy is the Lockheed team's complete redesign of the YF-22's entire shape and configuration in summer 1987 due to weight concerns, with prototype design freeze relatively soon afterwards resulting in its shape being rather unrefined and immature.<ref name="Hehs1998P2"/><ref>Mullin 2012, pp. 29-30.</ref> In contrast, the YF-23 was a continual refinement of Northrop's design concept even prior to Dem/Val proposal submission, with the configuration remaining largely the same throughout. Accurate artwork of the prototypes, which had been highly classified due to the stealth shaping, was first officially released in 1990 ahead of their public unveiling; the aforementioned Dem/Val extensions also pushed flight testing from 1989 to 1990. While the prototype air vehicle designs were frozen in 1988 in order to build the aircraft and begin flight tests by 1990, both teams continued to refine their F-22 and F-23 designs, or Preferred System Concepts, for full-scale development.<ref>Aronstein and Hirshberg 1998, p. 119.</ref><ref name="Metz2017p25-27"/><ref>{{Cite journal|title=Pentagon relaxes ATF design secrecy|journal=[[Flight International]]|location=London|publisher=Reed Business Information|issue=4217|volume=137|page=4|date=23–29 May 1990|url=http://www.flightglobal.com/pdfarchive/view/1990/1990%20-%201446.html|access-date=24 June 2011|archive-url=https://web.archive.org/web/20121105070635/http://www.flightglobal.com/pdfarchive/view/1990/1990%20-%201446.html|archive-date=5 November 2012|issn=0015-3710}}</ref>

[[File:YF-22 and YF-23 formation.png|thumb|Northrop team's YF-23 (above) and Lockheed team's YF-22 (below) flying in formation.]]
The first YF-23 made its maiden flight on 27 August 1990 and the first YF-22 first flew on 29 September 1990.<ref name=Goodall_p99>Goodall 1992, p. 99.</ref>  Flight testing began afterwards at [[Edwards Air Force Base]] and added the second aircraft for each competitor in late October 1990.<ref name=Miller_p38-9/>  The first YF-23 with P&W engines supercruised at Mach 1.43 on 18 September 1990 and the second YF-23 with GE engines officially reached over Mach 1.6 on 29 November 1990, topping out at Mach 1.72.{{refn|The YF-23 with the General Electric engines was officially stated to have been able to supercruise at over Mach 1.6, and estimates from General Electric engineers suggest that the top supercruise speed was as high as Mach 1.8.<ref>Sweetman 1991, p. 55.</ref><ref name="Chong2016p237-238"/>|group=N}}<ref name=Miller_p38-9/><ref name="test_pilot_interview">{{cite AV media |people=Metz, Alfred "Paul"; Sandberg, Jim |title=YF-23 DEM/VAL Presentation by Test Pilots Paul Metz and Jim Sandberg |date=27 August 2015 |publisher=Peninsula Seniors Production |location=Western Museum of Flight, Torrance, California |url=https://www.youtube.com/watch?v=Vpkv1ErWIf8 |access-date=15 September 2015}}</ref>  The first YF-22 with GE engines achieved Mach 1.58 in supercruise on 3 November 1990 and the second YF-22 with P&W engines also achieved Mach 1.43 on 27 December 1990. Maximum speed of both prototype designs in afterburner was in excess of Mach 2.{{refn|group=N|The YF119 did not yet incorporate the design changes for increased thrust and were still 30,000-lbf thrust engines, while the YF120 did and were 35,000-lbf thrust engines; as a result, both ATF prototypes achieved better performance with the GE engines.<ref>Aronstein and Hirschberg 1998, pp. 221-222.</ref>}}<ref name="Goodall_p102-3">Goodall 1992, pp. 102–103.</ref><ref>{{cite AV media |url=https://www.youtube.com/watch?v=nY0j3dmlHec |title=YF-22 - Road to the Raptor with Tom Morgenfeld, Test Pilot |date=17 April 2022 |publisher=Western Museum of Flight |location=Torrance, California |access-date=30 June 2023 |people=Morgenfeld, Thomas A.}}</ref> Flight testing continued until December 1990 with the YF-22s accumulating 91.6 flight hours in 74 sorties while the YF-23s flew 65.2 hours in 50 sorties. Following flight testing, the contractor teams submitted their ATF full-scale development proposals on 31 December 1990. The teams' NATF designs, often referred to as "[[Lockheed YF-22#NATF-22|NATF-22]]" and "[[Northrop YF-23#NATF-23|NATF-23]]" (they were never formally designated), were included in their proposals as well.<ref name=Miller_p38-9>Miller 2005, pp. 38–39.</ref>

==Selection and full-scale development==
{{main|Lockheed Martin F-22 Raptor}}
Following a review of the flight test results and proposals, the Secretary of the Air Force, Donald Rice, announced the Lockheed team and Pratt & Whitney as the competition winner for full-scale development, or Engineering and Manufacturing Development (EMD), on 23 April 1991. By this time, the 1990 Major Aircraft Review by Defense Secretary, Dick Cheney, had reduced the planned total ATF buy to 650 aircraft and peak production rate to 48 per year.<ref name="Miller_p38">Miller 2005, p. 38.</ref> Both air vehicle designs met or exceeded all performance requirements; the YF-23 was stealthier and faster, but the YF-22 was more agile.<ref name="Goodall_p110">Goodall 1992, p. 110.</ref> The U.S. Navy had begun considering a version of the ATF called Navy Advanced Tactical Fighter (NATF) in 1986,<ref name="Pace_p19-22">Pace 1999, pp. 19–22.</ref> and it has been speculated in the aviation press that the YF-22 was also seen as more adaptable to the NATF.{{refn|group=N|Both NATF-22 and NATF-23 would have been significantly different from their Air Force counterparts, with the NATF-22 having variable-sweep wings and the NATF-23 being shortened while having canards and a more conventional vertical tail arrangement.<ref>Miller 2005, p. 74.</ref><ref>Metz 2017, pp. 74-79.</ref>}}<ref name="Vector_F-22">{{usurped|1=[https://web.archive.org/web/20090106044034/http://www.vectorsite.net/avf22.html The Lockheed Martin F/A-22 Raptor]}}. Vectorsite.net, 1 February 2007.</ref> However, by late 1990 to early 1991, the Navy was beginning to back out of NATF due to escalating costs, and abandoned NATF completely by FY 1992.{{refn|The NATF peak production rate following the 1990 Major Aircraft Review was reduced to 36 per year, which further increased unit procurement costs and dissuaded the Navy from the program.<ref name="A&H1998p235-239"/>|group=N}}<ref name="Miller_p76">Miller 2005, p. 76.</ref>

[[File:F-22 Raptor flies during the AirPower over Hampton Roads Open House at Langley AFB Va., April 24, 2016.jpg|thumb|left|The production F-22 Raptor]]

The selection decision has been speculated by aviation observers to have involved industrial factors and perception of program management as much as the technical merit of the aircraft designs.<ref>{{cite report |author=Landis, Tony |date=1 February 2022 |title=Flashback: Northrop YF-23 Black Widow II |url=https://www.afmc.af.mil/News/Article-Display/Article/2919261/flashback-northrop-yf-23-black-widow-ii/ |publisher=Air Force Materiel Command History Office}}</ref><ref>{{cite web |last=Jouppi |first=Matthew |url=https://aviationweek.com/defense-space/aircraft-propulsion/what-usafs-ngad-program-can-learn-advanced-tactical-fighter |title=What USAF's NGAD Program Can Learn From The Advanced Tactical Fighter |work=Aviation Week & Space Technology |date=30 April 2024}}</ref> At the time, Northrop was viewed as riskier because it was struggling with the B-2 and [[AGM-137 TSSAM]] programs in terms of meeting cost, schedule, and predicted stealth performance.<ref name="Chong2016p237-238"/> In contrast, Lockheed's program management on the F-117 was lauded for meeting performance and delivering on schedule and within budget, with the aircraft achieving operational success over [[United States invasion of Panama|Panama]] and during the [[Gulf War]].<ref>Sweetman 1998, pp. 24-27.</ref> While the YF-23 air vehicle was in a higher state of maturity and refinement compared to the YF-22 due to the latter's late redesign and partly as a result had better flight performance, the Lockheed team executed a more aggressive flight test plan with considerably higher number of sorties and hours flown. Furthermore, Lockheed chose to execute high-visibility tests such as firing missiles and [[Stall (fluid dynamics)#Flight beyond the stall|high angle-of-attack maneuvers]] that, while not required, improved its perception by the USAF in managing weapons systems risk.<ref>Aronstein and Hirschberg 1998, pp. 159-160.</ref> With the overall final F-22 and F-23 designs competitive with each other in technical performance and meeting all requirements, the USAF decision then took into consideration non-technical aspects such as confidence in program management when determining the winner.<ref>Metz 2017, p. 73.</ref><ref>Aronstein and Hirschberg 1998, pp. 288-289.</ref><ref name="ATF_chief_eng">{{cite interview |last=Abell |first=Eric "Rick" |interviewer=C.W. Lemoine |title=Interview with Eric "Rick" Abell - Former Chief Engineer for the ATF Program |date=1 February 2021 |url=https://www.youtube.com/watch?v=_MUK241uZHM }}</ref>

The Lockheed team and Pratt & Whitney were awarded the EMD contracts to fully develop and build the Advanced Tactical Fighter in August 1991, initially worth $9.55 billion and $1.375 billion respectively for a total of approximately $11 billion (~${{Format price|{{Inflation|index=US-GDP|value=11000000000|start_year=1991}}}} in {{Inflation/year|US-GDP}}) as [[cost-plus contract]]s (which did eventually grow considerably). The YF-22 design was evolved and significantly refined to become the EMD/production [[Lockheed Martin F-22 Raptor|F-22 Raptor]] version,{{refn|group=N|The F-22 has a similar aerodynamic layout as the YF-22, but with notable differences in the overall external geometry such as wing sweep angle (reduced from 48° to 42°), the position and design of the cockpit, tail fins and wings, and in internal structural layout.<ref name="Hehs1998P2"/>}} which first flew in September 1997. However, with the [[dissolution of the Soviet Union]] in 1991 and the subsequent reductions in defense spending, the F-22's development would be "re-phased", or drawn out and extended multiple times. The program was scrutinized for its costs and less expensive alternatives such as modernized F-15 or F-16 variants were continually being proposed, even though the USAF considered the F-22 to provide the greatest capability increase against peer adversaries for the investment. Technology from the ATF would feed into follow-on tactical aviation programs such as the Joint Advanced Strike Technology (later renamed [[Joint Strike Fighter program|Joint Strike Fighter]]) that resulted in the [[Lockheed Martin F-35 Lightning II|Lockheed Martin F-35]]; for instance, the F-35's [[Pratt & Whitney F135|F135]] engine is a derivative of the F-22's F119.<ref>Aronstein and Hirschberg 1998, p. 250.</ref><ref>Sweetman 1998, pp. 88-89.</ref>

While the USAF adjusted its procurement goal down to 381 aircraft following the end of the Cold War, the funded number in the program of record continued to decline, dropping to 339 at a peak rate of 36 per year by the time the EMD/production aircraft first flew.<ref name="Miller_p38-46">Miller 2005, pp. 38, 42–46.</ref>  Both the F-22 and F-23 designs were later considered for modification as a medium-range supersonic regional bomber ([[Lockheed Martin FB-22|FB-22]] and [[Northrop YF-23#Proposed revival|FB-23]] respectively),<ref name="Miller_p38">Miller 2005, p. 38.</ref> but the proposals have not come to fruition.{{refn|group=N|Also competing with these regional bomber designs was the [[Rockwell B-1 Lancer#Variants|B-1R]]; plans for an [[2037 bomber controversy|"interim" regional bomber]] were dropped in the 2006 [[Quadrennial Defense Review]], which instead favored a larger strategic bomber with much longer range.<ref name="2018bomber"/>}}<ref name="2018bomber">Hebert, Adam J. {{usurped|1=[https://web.archive.org/web/20090923015849/http://www.airforce-magazine.com/MagazineArchive/Pages/2006/October%202006/10062018.aspx "The 2018 Bomber and Its Friends"]}}. Air Force magazine, October 2006.</ref> Following flight and operational testing, the F-22 entered service in December 2005, but with no apparent air-to-air threat present and the Department of Defense focused on [[counterinsurgency]] at that time, F-22 production only reached 195 aircraft — 187 of them operational models — and ended in 2011.<ref>{{Cite web|url=https://www.af.mil/News/story/storyID/123013572/ |title=F-22A Raptor goes operational |work=U.S. Air Force |date=15 December 2005 |access-date=24 June 2011 |archive-url=https://archive.today/20120723113239/http://www.af.mil/news/story.asp?storyID=123013572 |archive-date=23 July 2012 |url-status=live }}</ref><ref name= combataircraft>{{cite news |last=Parsons |first=Gary |url=http://www.combataircraft.net/view_article.asp?ID=4994 |title=Final F-22 Delivered |work=Combat Aircraft Monthly |publisher=Key Publishing |archive-url=https://web.archive.org/web/20160313044134/http://www.combataircraft.net/view_article.asp?id=4994 |archive-date=13 March 2016 |date=3 May 2012 |access-date=10 April 2014}}</ref>

==See also==
* [[F/A-XX program]]
* [[Have Dash]]
* [[Joint Strike Fighter program]]
* [[Next Generation Air Dominance]]

== Notes ==
{{reflist|group=N}}

==References==

===Citations===
{{Reflist|2}}

===Bibliography===
{{refbegin}}
* {{cite book |last1=Aronstein |first1=David C. |last2=Hirschberg |first2=Michael J. |last3=Piccirillo |first3=Albert C. |title=Advanced Tactical Fighter to F-22 Raptor: Origins of the 21st Century Air Dominance Fighter |location=Arlington, Virginia |publisher=AIAA ([[American Institute of Aeronautics & Astronautics]]) |year=1998 |ISBN=978-1-56347-282-4 |ref=none}}
* {{cite book |last=Chong |first=Tony |date=2016 |title=Flying Wings & Radical Things, Northrop's Secret Aerospace Projects & Concepts 1939-1994 |location=Forest Lake, Minnesota |publisher=Specialty Press |isbn=978-1-58007-229-8 |ref=none}}
* {{cite book |author=Goodall, James C. |chapter=The Lockheed YF-22 and Northrop YF-23 Advanced Tactical Fighters |title=America's Stealth Fighters and Bombers, B-2, F-117, YF-22, and YF-23 |location=St. Paul, Minnesota |publisher=MBI Publishing Company |year=1992 |ISBN=0-87938-609-6 |ref=none}}
* {{cite magazine|last=Hehs |first=Eric |title=Design Evolution of the F-22, Part 1 and 2 |url=https://www.codeonemagazine.com/f22_article.html?item_id=179 |publisher=Lockheed Martin |magazine=Code One |date=16 October 1998 |archive-url=https://web.archive.org/web/20240518062846/https://www.codeonemagazine.com/f22_article.html?item_id=179 |archive-date=18 May 2024 |ref=none}}
* {{cite book |author=Metz, Alfred "Paul" |title=Air Force Legends Number 220. Northrop YF-23 ATF |location=Forest Lake, Minnesota |publisher=Specialty Press |year=2017 |ISBN=0989258378 |ref=none}}
* {{cite book |author=Miller, Jay |title=Lockheed Martin F/A-22 Raptor, Stealth Fighter |location=Hinckley, UK |publisher=Midland Publishing |year=2005 |ISBN=1-85780-158-X |ref=none}}
* {{Cite book|author=Miller, Jay|title=Lockheed Martin's Skunk Works: The Official History...|location=Leicester, UK|publisher=Midland Publishing|year=1995|isbn=1-85780-037-0 |ref=none}}
* {{cite journal|last=Mullin |first=Sherman N. |title=Winning the ATF |url=https://secure.afa.org/Mitchell/reports/MP9_ATF_0612.pdf |journal=Mitchell Institute for Airpower Studies |publisher= Air Force Association |date=June 2012 |archive-url=https://web.archive.org/web/20210717131524/http://secure.afa.org/Mitchell/Reports/MP9_ATF_0612.pdf |archive-date=17 July 2021 |ref=none}}
* {{cite interview |last=Mullin |first=Sherman N. |interviewer-last1=Westwick |interviewer-first1=Peter |interviewer-last2=Deverell |interviewer-first2=William |title=Oral History Interview with Sherman Mullin. Second Interview. |work=Aerospace Oral History Project |date=24 January 2019 |publisher=[[Huntington Library|The Huntington Library, Art Museum, and Botanical Gardens]] |location=San Marino, California |url=https://hdl.huntington.org/digital/collection/p15150coll7/id/45049/ |archive-url=https://web.archive.org/web/20240808163832/https://hdl.huntington.org/digital/collection/p15150coll7/id/45049/ |archive-date=8 August 2024 |ref=none}}
* {{cite book |author=Pace, Steve |title=F-22 Raptor: America's Next Lethal War Machine |location=New York |publisher=McGraw-Hill |year=1999 |ISBN=0-07-134271-0 |ref=none}}
* {{cite book |author=Sweetman, Bill |title=YF-22 and YF-23 Advanced Tactical Fighters |location=St. Paul, Minnesota |publisher=Motorbooks International Publishing |year=1991 |ISBN=0-87938-505-7 |ref=none}}
* {{Cite book|author=Sweetman, Bill|title=F-22 Raptor|location=St. Paul, Minnesota, USA|publisher=Motorbooks International Publishing|year=1998|isbn=0-7603-0484-X |ref=none}}
{{refend}}

===Further reading===
{{refbegin}}
* {{cite book |last1=Jenkins |first1=Dennis R. |last2=Landis |first2=Tony R. |title=Experimental & Prototype U.S. Air Force Jet Fighters |location=North Branch, Minnesota |publisher=Specialty Press |year=2008 |ISBN=978-1-58007-111-6 |ref=none}}
* {{Cite book |last=Miller |first=Jay|title=Lockheed Martin's Skunk Works: The Official History|location=Leicester, UK|publisher=Midland Publishing|year=1995|isbn=1-85780-037-0 |ref=none}}
* {{cite conference |last=Mullin |first=Sherman N. |title=The Evolution of the F-22 Advanced Tactical Fighter |conference=Flight Simulation Technologies Conference |location=Hilton Head Island, South Carolina |doi=10.2514/6.1992-4188 |date=24–26 August 1992 |ref=none}}
{{refend}}

{{Advanced Tactical Fighter}}

[[Category:Military aircraft procurement programs of the United States]]
[[Category:Stealth aircraft]]