Editing Boeing E-3 Sentry (section)

==Development==
===Background===
In 1963, the USAF asked for proposals for an Airborne Warning and Control System (AWACS) to replace its [[Lockheed EC-121 Warning Star|EC-121 Warning Stars]], which had served in the [[airborne early warning]] role for over a decade.<ref>Wilson 1998, p.&nbsp;72.</ref> The new aircraft would take advantage of improvements in radar technology and computer-aided radar data analysis and data reduction. These developments allowed airborne radars to "[[Look-down/shoot-down|look down]]", i.e. to detect the movement of low-flying aircraft, and discriminate, even over land, target aircraft's movements; previously this had been impossible due to the inability to discriminate an aircraft's track from [[Radar#Clutter|ground clutter]].<ref name=Eden_p92>Eden et al. 2004, p.&nbsp;92.</ref> Contracts were issued to Boeing, [[Douglas Aircraft Company|Douglas]], and [[Lockheed Corporation|Lockheed]], the latter being eliminated in July 1966. In 1967, a parallel program was put into place to develop the radar, with Westinghouse Electric Corporation and Hughes Aircraft being asked to compete in producing the radar system. In 1968, it was referred to as Overland Radar Technology (ORT) during development tests on the modified EC-121Q.<ref name="AUR1">{{cite web |url=http://www.airpower.maxwell.af.mil/airchronicles/aureview/1972/may-jun/pearce.html |title=AWACS to Bridge the Technological Gap |access-date=14 February 2009 |publisher=Air University |archive-url=https://web.archive.org/web/20040627142853/http://www.airpower.maxwell.af.mil/airchronicles/aureview/1972/may-jun/pearce.html |archive-date=27 June 2004 |url-status=dead}}</ref><ref name="Davies p2">Davies 2005, p.&nbsp;2.</ref> The Westinghouse radar antenna was going to be used by whichever company won the radar competition since Westinghouse had pioneered the design of high-power [[radio frequency]] (RF) phase-shifters, which are used to both focus the RF into a pencil beam and scan electronically for altitude determination.

[[File:Lockheed RC-121C 1955.jpg|thumb|The piston-engined [[Lockheed EC-121 Warning Star|EC-121 Warning Star]], military version of the [[Lockheed Constellation]], saw service in the mid-1950s.|alt=Black-and-white photograph of piston-engined aircraft with a large hump on midfuselage]]
Boeing initially proposed a purpose-built aircraft, but tests indicated it would not outperform the already-operational 707, so the latter was chosen instead. To increase endurance, this design was to be powered by eight [[General Electric TF34]]s. It would carry its radar in a rotating dome mounted at the top of a forward-swept tail, above the fuselage.<ref name=Eden_p92/><ref>{{cite web|first=Erik|last=Simonsen|url=http://www.boeing.com/news/frontiers/archive/2007/march/i_history.pdf|title=Still keeping watch|date=March 2007|publisher=Boeing|access-date=21 August 2011|archive-url=https://web.archive.org/web/20110629074657/http://www.boeing.com/news/frontiers/archive/2007/march/i_history.pdf|archive-date=29 June 2011|url-status=live}}</ref> Boeing was selected ahead of [[McDonnell Douglas]]'s [[Douglas DC-8|DC-8]]-based proposal in July 1970. Initial orders were placed for two aircraft, designated EC-137D, as test beds to evaluate the two competing radars. As the test beds did not need the same 14-hour endurance demanded of the production aircraft, the EC-137s retained the [[Pratt & Whitney JT3D]] commercial engines, and a later reduction in the endurance requirement led to retention of the JT3D engines in production.<ref name="Davies p2"/><ref name="Janes 76 p246">Taylor et al. 1976, p.246</ref>

The first EC-137 made its maiden flight on 9 February 1972, with the fly-off between the two radars taking place from March to July of that year.<ref name=AUR1/> Favorable test results led to the selection of Westinghouse's radar for the production aircraft.<ref name="Davies 5-6">Davies 2005, pp.&nbsp;5–6.</ref> Hughes' radar was initially thought to be a certain winner due to its related development of the [[AN/APG-63 radar family|APG-63]] radar for the new [[McDonnell Douglas F-15 Eagle|F-15 Eagle]]. The Westinghouse radar used a pipelined [[fast Fourier transform]] (FFT) to digitally resolve 128 Doppler frequencies, while Hughes's radars used analog filters based on the design for the F-15. Westinghouse's engineering team won this competition by using a programmable 18-[[bit]] computer whose software could be modified before each mission. This computer was the AN/AYK-8 design from the B-57G program, and designated AYK-8-EP1 for its much expanded memory. This radar also multiplexed a beyond-the-horizon (BTH) pulse mode that could complement the pulse-[[Doppler radar]] mode. This proved to be beneficial especially when the BTH mode is used to detect ships at sea when the radar beam is directed below the horizon.<ref name="Northrop1">{{cite web |url=http://www.es.northropgrumman.com/solutions/awacs/assets/AWACS.pdf |title=AWACS Surveillance Radar |access-date=10 February 2009 |publisher=Northrop Grumman |url-status=dead |archive-url=https://web.archive.org/web/20090227021024/http://www.es.northropgrumman.com/solutions/awacs/assets/AWACS.pdf |archive-date=27 February 2009}}</ref>

===Full-scale development===
Approval was given on 26 January 1973 for the full-scale development of the AWACS system. To allow further development of the aircraft's systems, orders were placed for three preproduction aircraft, the first of which performed its maiden flight in February 1975. IBM and Hazeltine were selected to develop the mission computer and display system. The IBM computer was designated 4PI, and the software was written in [[JOVIAL]]. A [[Semi-Automatic Ground Environment]] (SAGE) or [[Back-Up Interceptor Control|back-up interceptor control]] (BUIC) operator would immediately be at home with the track displays and tabular displays, but differences in symbology would create compatibility problems in tactical ground radar systems in [[Iceland]], mainland Europe, and South Korea over [[MIL-STD-6011|Link-11 (TADIL-A)]]. In 1977, Iran placed an order for ten E-3s, however this order was cancelled following the [[Iranian Revolution]].

[[File:First E-3 Sentry at Tinker AFB.jpg|thumb|Welcome ceremony for first E-3 aircraft at [[Tinker AFB]] in 1977|alt=Black-and-white photograph with angled front view of four-engine jet aircraft on ramp with front fuselage door opened: A contingent of people are there to welcome the jet, which has a disc-shaped radar perching on top of struts on the dorsal fuselage.]]
Engineering, test and evaluation began on the first E-3 Sentry in October 1975. Between 1977 and 1992, a total of 68 E-3s were built.<ref name=USAF1>{{cite web|url=https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104504/e-3-sentry-awacs/|title=E-3 SENTRY (AWACS)|access-date=6 September 2017|date=22 September 2015|work=US Air Force|archive-url=https://web.archive.org/web/20170907122425/http://www.af.mil/About-Us/Fact-Sheets/Display/Article/104504/e-3-sentry-awacs/|archive-date=7 September 2017|url-status=live}}</ref><ref name = Boeing1/><ref>{{Cite web |date=2021-05-31 |title=45 years of Boeing E-3 Sentry - a brief history of AWACS — |url=https://afterburner.com.pl/45-years-of-boeing-e-3-sentry-a-brief-history-of-awacs/ |access-date=2024-01-04 |language=en-GB}}</ref>

===Future status===
Because the Boeing 707 is no longer in production, the E-3 mission package has been fitted into the [[Boeing E-767]] for the [[Japan Air Self Defense Force]]s. The [[Northrop Grumman E-10 MC2A|E-10 MC2A]] was intended to replace USAF E-3s—along with the [[Boeing RC-135|RC-135]] and the [[E-8 Joint STARS]], but the program was canceled by the [[United States Department of Defense|Department of Defense]].

NATO intends to extend the operational status of its AWACS until 2035 when it is due to be replaced by the [[Alliance Future Surveillance and Control]] (AFSC) program.<ref name="NATO summit Warsaw July 2016">NATO summit Warsaw July 2016</ref><ref>{{cite magazine |last=Warnes |first=Alan |date=December 2020 |title=Europe's New Look |magazine=AirForces Monthly |location=Stamford |publisher=Key Publishing|quote=Longer term, NATO is looking to a successor for the AWACS, when it is retired in 2035... the Alliance Future Surveillance and Control (AFSC) programme.}}</ref>  The [[Royal Air Force]] (RAF) chose to limit investment in its E-3D fleet in the early 2000s, diverting Sentry upgrade funds to a replacement program.<ref>{{cite magazine |last1=Lake |first1=Jon |date=December 2020|title=UK Wedgetail at risk? |magazine=AirForces Monthly |publisher=Key Publishing|quote=Any realistic opportunity to extend the E-3D in service was lost more than a decade ago, when the proposed Project Eagle upgrade was abandoned, and investment in the platform virtually ceased.}}</ref> On 22 March 2019, the UK Defence Secretary announced a $1.98 billion (~${{Format price|{{Inflation|index=US-GDP|value=1980000000|start_year=2019}}}} in {{Inflation/year|US-GDP}}) contract to purchase five [[Boeing E-7 Wedgetail]]s.<ref>{{cite web |url=https://www.raf.mod.uk/news/articles/wedgetail-to-be-rafs-new-early-warning-radar-aircraft/ |title=Wedgetail to be RAF's new early warning radar aircraft |publisher=Royal Air Force |date=22 March 2019 |access-date=22 March 2019 |archive-url=https://web.archive.org/web/20190322111155/https://www.raf.mod.uk/news/articles/wedgetail-to-be-rafs-new-early-warning-radar-aircraft/ |archive-date=22 March 2019 |url-status=live}}</ref> The U.S. Air Force intends to retire 15 of its 31 E-3s and acquire the E-7.<ref>{{cite web |title=US Air Force Picks Boeing E-7 Wedgetail as AWACS Replacement |url=https://www.thedefensepost.com/2022/04/28/usaf-wedgetail-awacs-replacement/ |website=The Defense Post |date=28 April 2022 |access-date=22 May 2022 |archive-date=25 May 2022 |archive-url=https://web.archive.org/web/20220525212143/https://www.thedefensepost.com/2022/04/28/usaf-wedgetail-awacs-replacement/ |url-status=live }}</ref>

On 31 March 2023, the USAF retired an E-3 from service for the first time.<ref>{{cite news |url=https://www.552acw.acc.af.mil/News/Article-Display/Article/3352309/552nd-acw-bids-farewell-to-first-awacs/ |title=552nd ACW Bids Farewell to First AWACS |last1=Bihlajama  |first1=Leyinzca  |date=6 April 2023 |website=af.mil |publisher=United States Air Force |accessdate=13 April 2023}}</ref>