Boeing E - 3 Sentry The Boeing E - 3 Sentry is an airborne early warning and control ( AEW & C ) developed by Boeing as the prime contractor . Derived from the Boeing 707 , it provides all - weather surveillance , command , control and communications , and is used by the United States Air Force ( USAF ) , NATO , Royal Air Force ( RAF ) , French Air Force and Royal Saudi Air Force . The E - 3 is distinguished by the distinctive rotating radar dome above the fuselage . Production ended in 1992 after 68 aircraft were built . In the mid - 1960s , the USAF was seeking an aircraft to replace its piston - engined EC - 121 , which had seen service for over a decade . After issuing preliminary development contracts to three companies , the USAF picked Boeing to construct two airframes to test Westinghouse Electric ' s and Hughes ' s competing radars . Both radars used Pulse - Doppler technology , with Westinghouse ' s design emerging as the contract winner . Testing on the first production E - 3 began in October 1975 . The first USAF E - 3 was delivered in March 1977 , and during the next seven years , a total of 34 aircraft were manufactured . NATO , as a single identity , also had eighteen aircraft manufactured , basing them in Germany . The E - 3 was also sold to the United Kingdom ( seven ) and France ( four ) and Saudi Arabia ( five , plus eight E - 3 derived tanker aircraft ) . In 1991 , by which time the last aircraft had been delivered , E - 3s participated in Operation Desert Storm , playing a crucial role of directing Coalition aircraft against the enemy . Throughout the aircraft ' s service life , numerous upgrades were performed to enhance its capabilities . In 1996 , Westinghouse Electric was acquired by Northrop before being renamed " Northrop Grumman Electronic Systems " , which currently supports the E - 3 ' s radar . Development . Background . In 1963 , the USAF asked for proposals for an AEW & C aircraft to replace its EC - 121 Warning Stars , which had served in the airborne early warning role for over a decade . The new aircraft would take advantage of improvements in radar technology which allowed airborne radars to " look down " and detect low - flying aircraft , even over land , which was previously impractical due to ground clutter . Contracts were issued to Boeing , Douglas and Lockheed , the latter being eliminated in July 1966 . In 1967 , a parallel program was put into place to develop the radar , with Westinghouse Electric and the 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 . The Westinghouse ' s radar antenna was going to be used whichever company won the radar competition , since Westinghouse had pioneered in the design of high - power RF phase - shifters . Boeing initially proposed a purpose - built aircraft , but tests indicated that 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 , or carrying its radar in a rotating dome mounted at the top of a forward - swept tail , above the fuselage . Boeing was selected ahead of McDonnell Douglas ' s 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 endurance requirement led to retaining the normal engines in production . The first EC - 137 made its maiden flight on 9 February 1972 , with the fly - off between the two radars taking place during March – July that year . Favorable test results saw the selection of Westinghouse ' s radar for the production aircraft . Hughes ' s radar was initially thought to be a certain winner , simply because much of its design was also going into the new F - 15 Eagle ' s radar program . 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 fighter . 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 . Full - scale development . Approval was given on 26 January 1973 for full - scale development of the AWACS system . To allow further development of the aircraft ' s systems , orders were placed for three pre - production aircraft , the first of which performed its maiden flight in February 1975 . To save costs , the endurance requirements were relaxed allowing the new aircraft to retain the four JT3D ( US Military designation TF33 ) engines . IBM and Hazeltine were selected to develop the mission computer and display system . The IBM computer receiving the designation 4PI , and the software is written in JOVIAL . A Semi - Automatic Ground Environment ( SAGE ) or 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 , Europe and Korea over Link - 11 ( TADIL - A ) . Modifications to the Boeing 707 for the E - 3 Sentry included a rotating radar dome , single - point ground refueling , air refueling , and a bail - out chute . The original design called for two bail - out chutes ( one forward , and one aft ) but the aft bail - out chute was deleted as a way to cut mounting costs . Engineering , test and evaluation began on the first E - 3 Sentry in October 1975 . During 1977 – 1992 , a total of 68 E - 3s were built . 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 E - 10 MC2A was intended to replace USAF E - 3s — along with the RC - 135 and the E - 8 — but the E - 10 program was canceled by the Department of Defense . The USAF is now performing a series of incremental improvements , mainly to avionics , to bring the E - 3 up to current standards of performance . Boeing is flight testing its Block 40 / 45 E - 3s . This modified E - 3 contains upgrades of the mission crew and air battle management sections , as well as significantly upgraded electronic equipment . Another program that the Air Force is considering is the " Avionics Modernization Program " ( AMP ) . AMP would equip the E - 3s with glass cockpits . The Air Force also wants modified E - 3s with jet engines that are more reliable than the original ones , and also with at least 19 % higher fuel efficiencies . New turbofan engines would give these E - 3s longer ranges , longer time - on - station , and a shorter critical runway length . If the modification is carried out , the E - 3s could take off with full fuel loads using runways only long , and also at higher ambient temperature s and lower barometric pressures , such as from bases in mountainous areas . Now that the E - 8 Joint STARS are being fitted with the new Pratt & Whitney JT8D - 219 turbofans , which are stated as having one - half the cost of the competing engine , the CFM56 , the Air Force is again studying the possibility of replacing the E - 3 ' s original turbofan engines with more - efficient ones . Design . Overview . The E - 3 Sentry ' s airframe is a modified Boeing 707 - 320B Advanced model . USAF and NATO E - 3s have an unrefueled range of some or eight hours of flying . The newer E - 3 versions bought by France , Saudi Arabia and the UK are equipped with newer CFM56 - 2 turbofan engines , and these can fly for about 11 hours or about . The Sentry ' s range and on - station time can be increased through air - to - air refueling and the crews can work in shifts by the use of an on - board crew rest and meals area . When deployed , the E - 3 monitors an assigned area of the battlefield and provides information for commanders of air operations to gain and maintain control of the battle ; whilst as an air defense asset , E - 3s can detect , identify and track airborne enemy forces far from the boundaries of the U . S . or NATO countries and can direct fighter - interceptor aircraft to these targets . In support of air - to - ground operations , the E - 3 can provide direct information needed for interdiction , reconnaissance , airlift and close - air support for friendly ground forces . Avionics . The unpressurized dome is 30 feet ( 9 . 1 m ) in diameter , six feet ( 1 . 8 m ) thick at the center , and is held 11 feet ( 3 . 4 m ) above the fuselage by two struts . It is tilted down 6° at the front to reduce its air drag during take - offs , and while flying endurance speed ( which is corrected electronically by both the radar and SSR antenna phase shifters ) . The dome uses both bleed - air and cooling doors to remove the heat generated by electronic and mechanical equipment . The hydraulically rotated antenna system permits the Westinghouse Corporation ' s AN / APY - 1 and AN / APY - 2 passive electronically scanned array radar system to provide surveillance from the Earth ' s surface up into the stratosphere , over land or water . Other major subsystems in the E - 3 Sentry are navigation , communications , and computers . Consoles display computer - processed data in graphic and tabular format on video screens . Console operators perform surveillance , identification , weapons control , battle management and communications functions . The radar and computer subsystems on the E - 3 can gather and present broad and detailed battlefield information . This includes position and tracking information on enemy aircraft and ships , and location and status of friendly aircraft and naval vessels . The information can be sent to major command and control centers in rear areas or aboard ships . In times of crisis , data can be forwarded to the National Command Authority in the U . S . via RC - 135 or naval aircraft carrier task forces . Electrical generators mounted on each of the E - 3 ' s four engines provide one megawatt of electrical power that is required by the E - 3 ' s radars and other electronics . Its pulse - Doppler radar has a range of more than 250 mi ( 400 km ) for low - flying targets at its operating altitude , and the pulse " beyond the horizon " radar has a range of approximately 400 mi ( 650 km ) for aircraft flying at medium to high altitudes . The radar combined with a secondary surveillance radar to provide a look down to detect , identify and track enemy and friendly low - flying aircraft while eliminating ground clutter returns . Upgrades . Starting in 1987 , USAF E - 3s were upgraded under the " Block 30 / 35 Modification Program " to enhance the E - 3 ' s capabilities . On 30 October 2001 , final airframe to be upgraded under this program was rolled out . Several major enhancements were made , firstly the installation of electronic support measures ( ESM ) and an electronic surveillance capability , for both active and passive means of detection . The Joint Tactical Information Distribution System ( JTIDS ) provides rapid and secure communication for transmitting information , including target positions and identification data , to other friendly platforms . Global Positioning System ( GPS ) capability was also added . Onboard computers were also overhauled to accommodate JTIDS , Link - 16 , the new ESM systems and to provide for future enhancements . The Radar System Improvement Program ( RSIP ) was a joint US / NATO development program . RSIP enhances the operational capability of the E - 3 radars ' electronic countermeasures , and dramatically improve the system ' s reliability , maintainability , and availability . Essentially , this program replaced the older transistor - transistor logic ( TTL ) and emitter - coupled logic ( MECL ) electronic components , long - since out of production , with off - the - shelf digital computer s that utilised a High - level programming language instead of assembly language . Significant improvement came from replacing the old 8 - bit FFT with 24 - bit FFTs , and the 12 - bit A / D ( Sign + 12 - bits ) with a 15 - bit A / D ( Sign + 15 - bits ) . These hardware and software modifications improve the E - 3 radars ' performance , providing enhanced detection with an emphasis towards low radar cross - section ( RCS ) targets . The RAF had also joined the USAF in adding RSIP to upgrade the E - 3 ' s radars . The retrofitting of the E - 3 squadrons were completed in December 2000 . Along with the RSIP upgrade was installation of the Global Positioning System / Inertial Navigation Systems which dramatically improve positioning accuracy . In 2002 , Boeing was awarded a contract to add RSIP to the small French AWACS squadron . Installation was completed in 2006 . Operational history . In March 1977 the 552nd Airborne Warning and Control Wing ( now the 552d Air Control Wing ) at Tinker AFB , Oklahoma received the first E - 3 aircraft . The 34th and last USAF Sentry was delivered in June 1984 . In March 1996 , the USAF activated the 513th Air Control Group ( 513 ACG ) , an ACC - gained Air Force Reserve Command ( AFRC ) AWACS unit under the Reserve Associate Program . Collocated with the 552 ACW at Tinker AFB , the 513 ACG which performs similar duties on active duty E - 3 aircraft shared with the 552 ACW . The USAF have a total of thirty - one E - 3s in active service . Twenty - seven are stationed at Tinker AFB and belong to the Air Combat Command ( ACC ) . Four are assigned to the Pacific Air Forces ( PACAF ) and stationed at Kadena AB , Okinawa and Elmendorf AFB , Alaska . One aircraft ( TS - 3 ) was assigned to Boeing for testing and development ( retired / scrapped June 2012 ) . In 1977 Iran placed an order for ten E - 3 ' s , however this order was cancelled following the 1979 revolution . NATO acquired 18 E - 3As and support equipment for a NATO air defense force . Since all aircraft must be registered with a certain country , the decision was made to register the 18 NATO Sentries with Luxembourg , a NATO member that previously did not have any air force . The first NATO E - 3 was delivered in January 1982 . The eighteen E - 3s were operated by Number 1 , 2 and 3 Squadrons of NATO ' s E - 3 Component , based at NATO Air Base Geilenkirchen . Presently 17 NATO E - 3As are in the inventory , since one E - 3 was lost in a crash . The United Kingdom and France are not part of the NATO E - 3A Component , instead procuring E - 3 aircraft through a joint project . The UK and France operate their E - 3 aircraft independently of each other and of NATO . The UK operates six aircraft ( with a seventh now retired ) and France operates four aircraft , all fitted with the newer CFM56 - 2 engines . The British requirement came about following the cancellation of the British Aerospace Nimrod AEW3 project to replace the Avro Shackleton AEW2 during the 1980s . The UK E - 3 order was placed in February 1987 , with deliveries starting in 1990 . The other operator of the type is Saudi Arabia which operates five aircraft , all fitted with CFM56 - 2 engines . E - 3 Sentry aircraft were among the first to deploy during Operation Desert Shield , where they immediately established as an around - the - clock radar screen to defend against Iraqi forces . During Operation Desert Storm , E - 3s flew 379 missions and logged 5 , 052 hours of on - station time . The data collection capability of the E - 3 radar and computer subsystems allowed an entire air war to be recorded for the first time in history . In addition to providing senior leadership with time - critical information on the actions of enemy forces , E - 3 controllers assisted in 38 of the 41 air - to - air kills recorded during the conflict . NATO and RAF E - 3s participated in the international military operation in Libya . Incidents and accidents . The E - 3 has been involved in three hull - loss accidents .