Airborne Early Warning
Airborne Early Warning [AEW] is the detection of enemy air or surface units by radar or other equipment carried in an airborne vehicle, and the transmitting of a warning to friendly units. Airborne early warning and control [AEW & C] is air surveillance and control provided by airborne early warning aircraft which are equipped with search and height-finding radar and communications equipment for controlling weapon systems.
The U.S. Navy, in 1944, under the threat of Kamikaze attack, ordered the development of a radar system that could be carried aloft in an aircraft. Which would expand the radar horizon under which the Fleet was to operate during a series of campaigns through the Philippines and northwards to Japan. Massachusetts Institute of Technology (MIT) was tasked with developing a workable system in February 1944 under Project Cadillac and a prototype system was built and flown in August on a modified TBM Avenger torpedo bomber. With tests proving successful, the system being able to detect low flying formations at a range in excess of 100 miles, the US Navy ordered production of the TBM-3W, the first AEW aircraft to enter service. TBM-3Ws fitted with the AN/APS-20 radar entered service in March 1945, with some 36-40 eventually being constructed.
The Avenger was purely an AEW radar aircraft, as the aircraft had a crew of only a single pilot and one radar operator. All control functions were conducted on surface ships, with radar data transmitted via a data link which gave the video image and radar antenna angle to enable a tactical picture to be developed in the Combat Information Center (CIC). Following the success of Project Cadillac, Project Cadillac II was commenced in 1944, with the aim of producing a flying command center. This lead to the development of the PB-1W, a modified B-17, using the same AN/APS-20 radar as the TBM-3W, but with several operators on board who could steer defending fighters towards targets via radio. The PB-1W was specifically designed to counter the Kamikaze threat, operating from land bases in support of the Fleet at sea.
The AN/APS-20 radar as fitted to the TBM-3W and PB-1W became the mainstay of AEW aircraft developments following World War Two. While not designed specifically as an AEW aircraft, the Grumman AF-2W Guardian, when fitted with the AN/APS-20 now had a secondary capability.
Experience with the Guardian led to the development of an AEW variant of the Douglas Skyraider piston engined attack aircraft. Once again the radar chosen was the AN/APS-20, with a large belly radome being fitted and a crew of three (one pilot and two operators) being carried. The Skyraider was eventually built in three versions, the AD-3W, AD-4W and AD-5W (which was later redesignated the EA-1E). As well as the U.S. Navy, the AD-4W was also supplied to the Royal Navy. With some 50 units being taken on charge as a cheap alternative to developing an AEW capability in Britain.
While these aircraft all suffered from technical limitations, experience gained by both the U.S. Navy and Royal Navy led directly to the development of more advanced and specialized AEW aircraft including the Lockheed Warning Star and Fairey Gannet AEW.
The Lockheed Warning Star began development as the US Navy PO-1W, an early model Constellation Airliner modified to carry experimental electronic surveillance equipment. After the PO-1W proved the concept of airborne early warning in large NATO exercises, the U.S. Navy and Air Force ordered large numbers of a developed variant based on the Lockheed Model 1049 Super Constellation. These aircraft entered service as the WV-2, 244 ordered, and the EC-121, 82 ordered of which 72 were from U.S. Navy orders.
The Warning Star entered service in 1955, with the final variants being retired from the U.S. Air Force Reserve in 1978. The Warning Star pioneered the concept of Airborne Early Warning and Control. With units being used for fleet coverage, airborne extension of the Distant Early Warning (DEW) Line, and in support of the Apollo Space Program.
USAF EC-121s were deployed to Vietnam in 1965 to provide early warning and communication relays. A USAF EC-121 made history in October 1967, when, while operating over the Tonkin Gulf off North Vietnam, it guided a U.S. Fighter to the successful interception of a VNAF Mig 21, the first time an airborne controller had directed a successful attack, setting the stage for many future developments in the area of AEW.
Throughout its life the Lockheed Warning Star was used to trial experimental radar and electronic equipment installations, including a radome installation on the WX-2E, later redesignated the EC-121L. After evaluation by the U.S. Navy the EC-121L was used as a prototype for evaluation of systems later installed on the E-3 Sentry.
Continuing a long tradition of AEW Aircraft development by Grumman, ranging from the Avenger and Guardian to the Hawkeye. The continuous improvements in early airborne radars by 1956 led to the concept of an airborne early warning and command and control aircraft. The first aircraft to perform this mission was the Grumman E-1 Tracer (a variant of the S-2 Tracker anti-submarine aircraft), which saw service from 1954 to 1964. The WF-2 Tracer was designed to replace the aging Guardians and Skyraiders providing AEW coverage for U.S. Navy aircraft carriers. The Tracer was developed from the S-2 Tracker anti-submarine warfare aircraft and first flew on March 1, 1957. The fitting of a large radome to the Tracer entailed significant modification from the standard ASW Tracker including the removal of the large single tail fin and replacing it with two end-plate fins on the tailplane.
The radar fitted to the Tracer was the new AN/APS-82 manufactured by Hazeltine, original builders of the AN/APS-20 which was the first AEW radar ever used. The AN/APS-82 introduced many technological advances including stabilized antenna and Airborne Moving Target Indicator (AMTI) which allowed the radar to detect low flying targets against the clutter of radar reflections from the surface of the ocean. 88 WF-2 and E-1B Tracers were built by Grumman for the U.S. Navy with operations extending from 1958 to 1977 when the E-2 Hawkeye completely replaced the aircraft in service.
The E-1's successor, the E-2 Hawkeye, was the first carrier-based aircraft designed from the outset for the all-weather airborne early warning and command and control function. Since replacing the E-1 in 1964, the Hawkeye has been the "eyes of the fleet." The Northrop Grumman E-2 Hawkeye is arguably the most widely used AEW&C aircraft in the world being in service with the United States Navy, and the air forces of Japan, Taiwan, Israel, Egypt, and Singapore. The French Navy are to be future users of the E-2 aboard the new aircraft carrier Charles de Gaulle. Developed as a replacement for the Grumman E-1 Tracer, the E-2 first flew in 1961 with the A model first seeing operational service off Vietnam in 1965. The current generation C model entered U.S. Navy service in 1973 and has been continuously developed since then. The latest version of the E-2C being designated Group II, with the Group II+ being developed for deployment in the near future.
The E-3 Sentry aircraft is a modified Boeing 707/320 commercial airframe with a rotating radar dome. Inside the dome is a radar subsystem that permits surveillance from the earth's surface up into the stratosphere, over land or water. The E-3 was originally conceived to overcome the line of sight limitations of ground based radar systems. At the time of its development AWACS was the first program to test the feasibility of a revolutionary new Air Force contract philosophy "fly before buy." Under this concept the prime contractor (Boeing) would have to provide a viable end product, flown, tested and thoroughly analyzed before the initial delivery would take place.
The primary mission of the AWACS prior to the end of the Cold War was as an airborne early warning radar, alerting North American Aerospace Defense Command to the approach of Soviet Union bombers if they flew toward the United States or Canada. AWACS has been involved in every major operation over the last 25 years. It is simply an asset America counts on every time for surveillance, weapons control, and battle management.
US policy requires the radar and mission systems for E-3 and E-767 AWACS, E-2C, and C-130J using the E-2C mission system be sold via FMS. The purpose of this policy is to ensure interoperability, compatibility, supportability, releasability, fleetwide commonality for future upgrades, and compliance with technology transfer policy issues. However, commercial AEW&C systems are being offered to U.S. allies for military use through direct commercial sales under export licenses with little Department of Defense (DoD) insight into the final technology being transferred and no assurance that the delivered systems will be interoperable/compatible with DoD systems in coalition operations. It is in the best interest of the Government to have more DoD involvement in direct commercial sales that include AEW&C systems.
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