Boeing E-3A AWACS Early Warning

“I love the mission. I love the fact that we’re the eyes and ears. That’s the coolest part.” — Airman Nicholas Cotter, Radar Technician, 552d Air Control Wing.

Boeing E-3A AWACS

The Boeing E-3A AWACS

As Airman Cotter indicates, the crews of the modern Airborne Warning and Control System (AWACS) aircraft understand that they are doing more than controlling battles, interdicting drug traffic and monitoring weather systems. They know that their AWACS aircraft is the perfect instrument for national power projection. The AWACS is not provocative, as it has no-board offensive capability. Yet it is so vital a part of modern warfare that its very presence in a potential trouble spot gives assurance that the intentions of the United States are serious.

The AWACS debuted only after many decades of experimentation with airborne early warning (AEW), and in response to extremely varied threats. Whereas the first airborne AEW aircraft were dedicated to fleet defense or anti-submarine warfare, later generations were intended as barriers to bombers attacking North America. The intercontinental ballistic missile threat diminished the usefulness of barrier aircraft even as the utility of airborne command and control centers were proven in the Vietnam War.

The first attempts at seeing “over the next hill,” that long sought goal of ground-bound generals, were achieved by balloons and then observation aircraft. These became important in World War I, despite the limits imposed by night and weather. Primitive acoustic listening devices, used in cooperation with ground observers, were developed to detect raids by Zeppelins and bombers. But the first really successful instrument for detecting incoming bombers was radar, developed simultaneously in several countries. The famous English “Chain Home” radar system was vital to the Royal Air Force’s victory in the Battle of Britain. During World War II, radar played an increasingly important role on land, sea and air.

Yet ground-or sea-based radar had inherent limitations as an early warning system. While it could see farther than the human eye and was useful at night and in bad weather, it still could not see over another “next hill”–the curvature of the earth.

During World War II, an attempt to extend the radar horizon by allowing ships to tie their radar information in an early “network centric” concept was proving unsuccessful just as the Japanese Kamikaze attacks accelerated. Fortunately, studies by Captain Frank Akers and Lieutenant Commander Lloyd V. Berkner of the Bureau of Aeronautics in early 1944 were focused on an airborne aerial warning system. Working with the Massachusetts Institute of Technology-Radiation Laboratory on Project NA-178 (later called “Cadillac I” after the nearby Cadillac Mountain.) the military/academic team delivered the first production AEW system in only thirteen months.

The capability of the new airborne radar equipment, designated APS-20, was even more remarkable than its speed of delivery, for it was used with little modification for many years to come in a wide variety of airframes and applications.

The APS-20 was tested initially in the Grumman (General Motors) TBM-3W, a version of the hardy Avenger torpedo plane. The radar’s eight by three foot paraboloid dish antenna was housed in a huge ventral dome. The need for greater range and endurance as well as some command and control capability led to having the APS-20 installed in the Boeing PB-1W. Some twenty-five of these converted B-17Gs were delivered under project Cadillac II.

In these old but proven aircraft the new radar system began one revolution in warfare while hinting at another. The first revolution, airborne early warning, immediately allowed fleet commanders to see hostile forces long before they could attack. The second revolution, service as an airborne combat information center, would be foreseen but not realized for many years.

The APS-20’s gain in search capability varied from two to six times that of ship-based radar, depending upon the target. Yet this advantage was somewhat offset by implicit problems including the need to compensate for the motion of the aircraft, equipment cooling requirements, the difficulty in discriminating targets from ground clutter and the limited computer processing capability available at the time.

And while the APS-20 was an outstanding advance, it was only one half of the system. The aircraft had a radar receiver with an IFF (identification friend or foe) receiver, and a complex synchronizer. The two man crew used three radar consoles to correlate information, their task made difficult by the lack of symbology. Instead of the today’s familiar array of symbols, returns on the radar screens were only yellow flashes, jokingly termed “florescent bananas.” These were tracked by grease pencil, and establishing a target’s course and speed took as much as three minutes.

The other half of the system was on board ships, where the additional space, power and cooling available allowed it to be much more elaborate. The shipboard equipment included a radar relay service to the combat information centers on other ships, conveying data on units of the fleet as well as on unidentified targets.
Over the years, the Navy expanded the use of the APS-20 in a number of carriers, including the Grumman Guardian, Douglas Skyraider, Lockheed Neptune, and the ZPG-3W blimp.

A Barrier to the Bull

In the very early years of the Cold War, the Soviet Union developed nuclear and thermonuclear weapons far more rapidly than had been anticipated. It also created a delivery system with the incredible reverse engineering of three interned Boeing B-29s to create a fleet of several hundred Tupolev Tu 4 Bull bombers. The Soviet Union was able to launch a massive nuclear attack by sending Bulls on a one-way mission. An American air defense system was necessary, one which could detect such an attack in its early stages and muster the weaponry to defeat it.

The air defense system included ground and sea-based radar stations, a series of new interceptor aircraft, and later, surface to air missiles. In 1950, the first system consisted of 43 radar sites augmented by the recall to active duty of 36 Air National Guard fighter units. The radar capability was integrated into the Semi-Automated Ground Environment System (SAGE) to control fighters. By 1954, the USAF and Royal Canadian Air Force had completed the Pinetree Line, consisting of 33 individual stations on both sides of the international border. There followed, in remarkably quick succession, the Canadian-built Mid-Canada line and the Distant Early Warning Line (DEW line). The latter ranged from Alaska to Greenland. Both were operational by 1957, and all three lines were integrated into the SAGE system. Later, these lines were supplemented in 1963 by the Ballistic Missiles Early Warning System.

As expensive, extensive and effective as these land-based radar lines were, they obviously could be outflanked by attacks coming across the ocean. The need for picket ships and early-warning aircraft was identified as early as 1946. No action was taken because of limited budgets and difficulties in resolving roles and missions issues.

In the early 1950s, the Navy accepted the challenge of an airborne early warning barrier by acquiring 142 examples of the Lockheed WV-2 Warning Star, derived from the Super Constellation Model 749 airliner. The APS-20 radar was housed in a plastic radome underneath the aircraft and was supplemented by an APS-45 height-finding radar. While intended primarily for use in barrier flights (termed SEADEW), the Navy exploited the Warning Star’s capabilities by using it for hurricane hunting, weather reconnaissance, and fleet support.

The Air Force followed suit, adopting the WV-2 to its needs as the RC-121C, its first airborne early warning aircraft. Ten of these were delivered in late 1953, and were used with Navy radar picket ships as an extension of the Continental Air Defense System of the United States.

Within two years, after the usual long series of changes in bases and designations, the USAF airborne early warning force had grown to six squadrons and fifty aircraft operating in two wings (551st and 552d AEW&C) under the Eighth Air Division.

Duty on the RC-121s was arduous. Flight crews were nominally five officers and thirteen enlisted personnel, but this could be more than doubled for longer missions. Tracking the APS-20’s “fluorescent bananas” was demanding, and operators at the five radar consoles were relieved often during a sixteen hour mission. Takeoff and on-station times were critical and were made almost without regard to prevailing weather conditions. Some sixty percent of USAF barrier missions were flown in icing conditions, while fifty percent encountered storm-force winds.

The Super Constellation was powered by the temperamental Curtiss Wright R-3350 urbo-compound engines, similar to those that caused so much difficulty in B-29 operations. Engine malfunctions and fires were often encountered as were hydraulic leaks, and these seemed to occur most often when the aircraft were on station, hundreds of miles out to sea. Over the years, at least fifty crew members were lost supporting this massive effort.

By the 1960s it was apparent that the principal Soviet threat was from ICBMs, and the perceived need for barrier aircraft declined. AEW operations were expensive, and there was some concern about just how effective they were. The combined maintenance problems of the Super Constellation and the increasingly antiquated APS-20 equipment called for changes in mission and equipment.

The Navy sought improvement with the introduction of the Grumman E-2 Hawkeye, equipped with the new APS-82 radar and a rotating dome over the fuselage. Knowing that a long development time was required before the E-2 became operational, the Navy selected the Grumman E-1B as an “interim” aircraft, one that served for twenty years. Known colloquially as the “Willy Fudd” or the “Stoof with a Roof”, the E-1B also used the APS-82 installed in a fixed, air-foil shaped housing mounted over the fuselage.

The Air Force continued to use its EC-121s to assist in tracking and recovering space vehicles and providing command and control for nuclear tests. Other duties included shepherding fighter aircraft on long over-water deployments, filling in for inoperative land-based radar sites and acting as a control vehicle on flights of Air Force One. They were especially effective during the Cuban missile crisis, protecting U-2s from MiG attacks.

The Vietnam War forced a different tack after 1965, as the EC-121s were pressed into service to augment surface based radar. The 552d Wing’s EC-121s were first designated as the Big Eye Task Force; the name was later changed to College Eye Task Force. Aircraft based in Taiwan, South Vietnam and Thailand were rotated into the theater on a continuous basis. flying combat missions until 1973. During that time they provided control to 210,000 aircraft, issued 3,297 threat warnings and assisted in the rescues of more than 80 downed aircrew members.

The College Eye EC-121s flew a race-track orbit over the Gulf of Tonkin, with initial emphasis on monitoring enemy air activity and controlling U.S. fighter aircraft in the area. As users became aware of the 552d’s capabilities, its duties were expanded to include battle management of combat air patrol, strike and support missions, coordinating search and rescue operations, controlling air refueling operations and acting as an airborne radio relay for post-strike reports.

By 1967, the EC-121’s were operating over Laos, to provide navigational assistance to U.S. aircraft and to prevent incursions across the border to China. Later these aircraft moved closer to North Vietnam, where operating under the call sign “Disco” they directed airborne intercepts against North Vietnamese fighters.

The veteran EC-121 crews wrung the utmost from their outdated equipment which had difficulty in discriminating aircraft against the clutter of the Vietnamese land mass. On 10 July 1965 “Disco” vectored two McDonnell F-4C of the 45th Tactical Fighter Squadron in an attack which shot down two MiG-17s, in the first radar-assisted kill of the war.

The 552d won five Air Force Outstanding Unit Awards, two for valor, for its operations in the Vietnam War. Perhaps even more important, the antiquated, oil-leaking, prone-to-failure EC-121’s validated the need for an advanced airborne early warning aircraft.

NATO AWACS on takeoff.

NATO AWACS on takeoff.

The Advent of AWACS

The Navy’s Hawkeye had a long and often disheartening development period—the program was cancelled on one occasion–but finally emerged as an exceptionally robust and capable AEW aircraft. However, it was too small and short-ranged to fulfill USAF requirements, which were partially met on an interim basis by upgrades to the veteran EC-121s which also served as test beds. The most important of these upgrades was a pulse-Doppler radar system that solved the problem of ground clutter. In addition there were added a digital datalink, data symbology, computer aided tracking, IFF tracking, and secure beyond-line-of-sight voice capability. Software was vastly improved. The new equipment resulted in an airborne early warning system that could also serve as a command and control aircraft.

Air Force Systems Command’s Electronic Systems Division at Hanscom Air Force Base, Massachusetts led in the development of long-range pulse Doppler radar and issued Specific Operational Requirement 206, Airborne Warning and Control Systems (AW&CS) in 1963. On December 22, 1965, the AW&CS System Program Office was established, coming under the direct supervision of the Secretary of Defense. The AW&CS SPO established the ground rules for a long, complex competition for both air frame and radar manufacturers.

Boeing’s 707 won the airframe competition over the McDonnell Douglas DC-8 platform on July 10, 1970. Two 707s (designated EC-137 for the purpose) were outfitted with the competing Hughes and Westinghouse radar systems and were extensively tested. Westinghouse APY-1 radar was declared the winner in 1972, and the official USAF AWACS production effort began on January 26, 1973.

Almost from its inception, the AWACS program experienced scathing attacks by the media, being labeled in April, 1974 by the New Republic as “AWACS: The Plane That Would Not Die.” It stated that the AWACS looked like a “mushroom with elephantiasis”, a reference to the thirty-foot wide rotating radar dome stationed eleven feet above the aircraft’s fuselage. Perhaps even more damaging were two General Accounting Office reports. One questioned the ability of the AWACS to operate in a hostile environment, while the other criticized the ability of the AWACS to function in the face of Soviet electronic jamming equipment. Much of the hostility was generated by the fact that it was the first weapon system to cost $100,000,000 a copy.

Fortunately, the predictions of the New Republic were proved wrong from the start, and next June, the magnificent Boeing E-3 Sentry will celebrate thirty years of being an ever more important element of the United States’ military might.

More than AEW

The very first AEW squadron, the 4701st Airborne Early Warning and Control Squadron was established on October 1, 1953. Over the next twenty years, there was a long and complicated series of reorganizations and re-designations, but on July 1, 1976, the Air Force recognized the outstanding wartime service of the 552d Airborne AEW&C group by establishing the 552d Airborne Early Warning and Control Wing (AEW&C) at Tinker Air Force Base, Oklahoma. The 552d (now the 552d Air Control Wing) amply justified the recognition in many operations and many wars over the next three decades.

The first production E-3 was rolled out in October, 1976, only 23 months after Boeing was ordered to proceed. The following March 24, the first aircraft, tail number 50557, was delivered to the 552d at Tinker Air Force Base. There General Robert Dixon, Commander of Tactical Air Command, promptly christened the E-3 as the “Sentry”, allegedly against legal advice about copyright infringement.

The Air Force hoped to buy 42 E-3s, but budgetary restrictions reduced this to 33, the last of which was delivered in late 1984. (Thirty-four were built, including a Boeing test bed. One aircraft, call sign YUKLA-27, was lost shortly after take-off at Elmendorf Air Force Base, Alaska on September 22, 1995, when it encountered a huge flock of Canada geese. All twenty-four members of the crew died in the crash.) At its peak of thirty-two aircraft, the fleet is far smaller than the scores of EC-121s which it replaced.

The E-3’s dramatic improvement in capability was due in almost equal parts to the airframe and the new radar systems which allow it to provide all-weather surveillance over any type of terrain. The onboard IBM System 4Pi computer gave the E-3 ample process power. Outfitted with 14 computer and radar workstations, it carries from 20 to 30 mission crew members and four flight crew.

The E-3 crews see the enemy and tell our fighters where he is. The Boeing 707-320 airframe conferred many advantages, for it was much more reliable and less maintenance dependent than the EC-121s. Its vastly higher speed and incredible range with aerial refueling meant that it could carry the flag to distant trouble spots quickly with greater crew comfort. The Sentry’s higher altitude capability endowed its superior radar with a far greater range. The much greater available electrical power permitted additional equipment to be installed as it was developed. With its million-watt, Doppler radar system, the AWACS was the first successful example of look-down, shoot-down capability. It is particularly successful against low-flying, earth-hugging air targets, and is capable of precision tracking and control of both airborne and maritime targets while remaining highly-resistant to electronic counter measures.

The Westinghouse APY-1 radar was exceedingly complicated by today’s standards, containing some 78,000 parts, but it had a range of 250 miles, and could distinguish aircraft tracks from ground clutter, a key factor. Mounted back to back with the Mark XII IFF and the TADIL-C datalink antennas, it could operate in five different modes, including detecting targets at low altitudes, detecting targets and their elevation, looking beyond-the-horizon for long range surveillance, with receivers only for passive surveillance, and test and maintenance.

For the operators, the most obvious advance was the introduction of symbols on the radar screens rather than the raw data of fluorescent flashes. The new radar was much more flexible, and allowed the operator to manipulate the data for better analysis and display. And, to offset the fears about is inability to operate in the face of Soviet jamming, the Sentry’s radar operators had their own sophisticated electronic counter measures equipment.

One of the remarkable aspects of the AWACS is the manner in which the crew can “force multiply the force multiplier” by their expertise with the equipment. Experience makes them such masters of the equipment that it speaks to them in ways unseen in the tech orders, endowing the E-3 with a far greater capability than anyone had planned.

The AWACS in Operation

The AWACS signaled a new era in the concept of airborne battle management even as it became the flagship of aerial diplomacy. The 552d’s E-3s were at once perceived as essential to any combat operation, and were immediately in constant demand for training exercises. They are eminently suitable for counter-narcotic operations in Central America. Most importantly, E-3s are committed to actual combat operations as they arise. These ranged from passive duties such as surveying border disputes between North and South Yemen to battle action in Grenada, Panama, the Middle East and the Balkans.

The 552d particularly distinguished itself during Operation Desert Shield and Desert Storm, flying 7,314.7 combat hours and controlling 31,924 strike sorties. In addition, the AWACS controlled 20,401 air refueling sorties where tankers offloaded 178 million gallons of gas to 60,453 receivers. When the Gulf War ended, the E-3s were essential to peace-keeping in Operations Provide Comfort, Northern Watch and Southern Watch. In January, 1993, an F-16 was guided so that it could intercept and destroy a wayward Iraqi MiG 29.

On April 14, 1994, there occurred a “blue on blue” tragedy in which two U.S. Army UH-60 Blackhawk helicopters were shot down, with a loss of twenty-six personnel. The accident occurred when the monitoring AWACS became confused as to their location. The UH-60s were identified as Iraqi Hind’s, and shot down by two USAF F-15s. In the subsequent investigation, mistakes were attributed to both the AWACS crew and the F-15 pilots.

In the autumn of the same year, the United States used E-3s in working with several Caribbean nations in Operation Uphold/Maintain Democracy, the restoration to power of Hati’s president Jean-Bertand Aristide. Halfway across the world, other E-3s helped quell Iraq when it threatened another invasion of Kuwait.

In 1995, NATO E-3s monitored the 3,515 NATO sorties in Operation Deliberate Force. During the same year, after almost twenty years of continuous service, the Block 30/35 upgrade, the single largest improvement to E-3 equipment began, affecting four major subsystems. These included the integration of the Joint Tactical Information Distribution Systems, Global Position System, Electronic Support Measures System and Data Analysis Program Group. All E-3s were modified by September, 2001.

When the Air Expeditionary Force became the Air Force’s standard mode of operation in 1997, the 552d was well positioned to support it, despite the relatively small number of aircraft in its fleet. Its long experience in sending small numbers of E-3s to all corners of the globe for long periods of time served it well, enabling it to meet each major military requirement as it happened. E-3s were on hand to support such Operations as Desert Thunder, Desert Fox, and Allied Force. The unrelenting acceleration in operations tempo became a way of life to the 552d.

In 1999, more than a score of E-3s took part in Operations Allied Force, flying 500 missions averaging almost ten hours each, and contributing to the destruction of about eighty-five percent of Yugoslav air force fighters. In the same year, the E-3s were again enhanced, this time with the Radar System Improvement Program (RSIP), a joint U.S./NATO development effort.

The terrorist attacks on September 11, 2001, brought new work to the 552d. Tasked to protect the airspace over North America, it flew hundreds of missions as part of Operation Noble Eagle, including 460 in the last year. Yet the demand for AWACs support world wide was so great that five NATO E-3s had to be summoned to assist in defending the United States, flying an additional 380 missions as part of Operation Eagle Assist.

The incredible value and importance of the AWACS as a force multiplier was brought home most forcefully in Operations Enduring Freedom and Iraqi Freedom. In both of these campaigns, the E-3s, the epitome of Low Density/High Demand assets, were key instruments in establishing air dominance.

The E-3s possessed the requisite long loiter time, extraordinary communication capability, long-range radar and, most of all, the ability to integrate information derived from satellites with ground and air based assets. In OIF, the AWACS flew more than 400

missions and 5,000 flying hours to guide 120,000 sorties by coalition forces, and took part in thirty-eight of the forty aerial victories gained.

The Sentry, bombers and the Combined Air Operations Center worked together seamlessly to speed up the “kill chain,” as defined by the target cycle of “Find Fix, Track, Target Engage and Assess.” One of the most notable instances was the April 7, 2003 attack by a 405th AEW Boeing B-1B on Saddam Hussein’s presence in the al-Saa restaurant in Baghdad. (The 405th AEW was commanded by then Colonel, now Major General James Kowalski, who currently commands the 552d ACW.) The “normal” kill chain time of about forty-five minutes was reduced to just twelve after AWACS informed the B-1B of the target. Although the bombs arrived just moments after Hussein had departed, it was still a remarkable demonstration of the AWACS and B-1B’s capability to shorten the kill chain.

The AWACS continues to be a fundamental keystone in the United States’ military capability. It is augmented by other aerial systems including the Boeing RC-135 Rivet Joint, Boeing E-2C, Grumman Hawkeye, Lockheed Martin EP-3 Orion and U-2, Beech RC-12 Guardrail, General Atomics Aeronautical Systems Predator and Northrop Grumman RQ-4 Global Hawk. And it has an almost exact counterpart for ground operations in the Northrop Grumman E-8C Joint Surveillance Target Attack Radar System (Joint STARS). Also a modified Boeing 707, the Joint STARS provides detection of moving and stationery targets on the ground, along with slow-moving targets and theater missile defense targets.

In addition to its combat duties, AWACS aircraft have been made available through the years for domestic crises, such as the 1995 Oklahoma City bombing or such weather disasters as 2005’s Hurricane Katrina.

Foreign AEW Systems

Many nations had a long history of using AEW systems, but the immense combat capabilities of the AWACS were perceived immediately. Many countries procured examples of the E-3 or developed an indigenous version of it. E-3s were exported as follows: the United Kingdom, seven; France, four, NATO, eighteen and Saudi Arabia, five (along with six KE-3 tankers.)

Today at least thirty-six air forces are operating AEW aircraft of some kind, and the number will only grow in the future.

Somewhat surprisingly, Soviet technological expertise was not as much in evidence in their AEW systems, and the Tupelov Tu-126 Moss was produced and operated in relatively small numbers, given the massive size of the Soviet Air Force. The Moss was apparently used by India in its 1971 war with Pakistan. The Ilysushin Il-76 transport was adapted for AWACS use as the A-50. It was code-named MAINSTAY by NATO, but generally referred to as the Soviet AWACS.

The Future of AWACS

The history of AWACS has been that of continual improvement through up-grade programs, and this will continue into the future for some time. One important upgrade program may be the installation of up-rated engines. As the 707-320 airframe is no longer in production, future AWACS, like the four purchased by Japan, will be based on more modern airframes, such as the Boeing 767. Other examples of AWACS, with alternate electronic systems and smaller airframes, are being put forward in various countries around the world.

In the United States, it may be that the functions of AWACS and Joint STARS will be combined in a single aircraft, one that might also have a tanker capability.
But in the very long run there are two other alternatives. AWACS may be delegated to a completely new platform, such as ground sensor units, Unmanned Aerial Vehicles (UAVs) or a space sensor. As an example, a ground C2 facility might be connected via satellite communications into a theater data-link network that might include Lockheed Martin F-22s which would then perform the sensor functions of a “mini-AWACS.” Alternatively, it may be that airborne warning and control functions may be divided among a whole range of assets, including manned and unmanned types, located on the ground, in the air or in space. These developments are perhaps two decades in the future, and even after they arrive, will almost certainly still be supported by the E-3 and its derivatives.


All E-3 AWACS aircraft undergo a Programmed Depot Maintenance cycle every four years to correct defects, install new equipment and insure that the aircraft is structurally sound. This process is projected to be continued until all but five of the E-3s are retired in 2025.

The initial E-3A had a CC-1 computer and nine Situation Display Consoles. All but one of the 23 E-3A production aircraft had the APY-1 radar; one was completed with the APY-2 and the CC-3 computer. Two refurbished EC-137D test beds were similarly equipped.

Under the Block 20 program, 24 of the original aircraft were modified to E-3B status, with five more Situation Display Consoles, a new computer, radio teletype and maritime surveillance capability, along with other improvements.

Ten aircraft became E-3Cs under the Block 25 program uprgrade, being equipped with the AN/APY-2 surveillance radar. It also has the Have Quick anti-jamming equipment. The E-3C, upgraded under the Block 25 program, is similar to E-3A with 5 more Situation Display Consoles (SDC) and Have Quick anti-jamming equipment.

A Block 40/45 program is scheduled for the future, and will replace much of the aging equipment with new off the shelf operator stations linked to off-the-shelf computers.

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