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. 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. Initial orders were placed for two aircraft, designated EC-137D, as test beds to evaluate the two competing radars. Boeing was selected ahead of McDonnell Douglas's DC-8-based proposal in July 1970. It would carry its radar in a rotating dome mounted at the top of a forward-swept tail, above the fuselage. To increase endurance, this design was to be powered by eight General Electric TF34s. The piston-engined EC-121 Warning Star, military version of the Lockheed Constellation, saw service in the mid-1950s.īoeing initially proposed a purpose-built aircraft, but tests indicated it would not outperform the already-operational 707, so the latter was chosen instead. 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. In 1968, it was referred to as Overland Radar Technology (ORT) during development tests on the modified EC-121Q. 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. Contracts were issued to Boeing, Douglas, and Lockheed, the latter being eliminated in July 1966. 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 ground clutter. These developments allowed airborne radars to " look down", i.e. The new aircraft would take advantage of improvements in radar technology and computer-aided radar data analysis and data reduction. In 1963, the USAF asked for proposals for an Airborne Warning and Control System (AWACS) to replace its EC-121 Warning Stars, which had served in the airborne early warning role for over a decade. Air Force announced that the Boeing 737 AEW&C is to replace the E-3 beginning in 2027. In 1996, Westinghouse Electric's Defense & Electronic Systems division was acquired by Northrop Corporation, before being renamed Northrop Grumman Mission Systems, which currently supports the E-3's radar.
The aircraft's capabilities have been maintained and enhanced through numerous upgrades. In 1991, when the last aircraft had been delivered, E-3s participated in the Persian Gulf War, playing a crucial role of directing coalition aircraft against Iraqi forces. E-3s were also purchased by NATO (18), the United Kingdom (7), France (4) and Saudi Arabia (5). The first USAF E-3 was delivered in March 1977, and during the next seven years, a total of 34 aircraft were manufactured. Testing on the first production E-3 began in October 1975. Both radars used pulse-Doppler technology, with Westinghouse's design emerging as the contract winner. After issuing preliminary development contracts to three companies, the USAF picked Boeing to construct two airframes to test Westinghouse Electric and Hughes's competing radars. Air Force (USAF) was seeking an aircraft to replace its piston-engined Lockheed EC-121 Warning Star, which had been in service for over a decade. Production ended in 1992 after 68 aircraft had been built. The E-3 has a distinctive rotating radar dome (rotodome) above the fuselage. Derived from the Boeing 707 airliner, it provides all-weather surveillance, command, control, and communications, and is used by the United States Air Force, NATO, French Air and Space Force, Royal Saudi Air Force and Chilean Air Force. E-3s are commonly known as AWACS (Airborne Warning and Control System). The Boeing E-3 Sentry is an American airborne early warning and control (AEW&C) aircraft developed by Boeing.
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