Lockheed C-69 Constellation

Vietnam War


EC-121s were used extensively in Southeast Asia between 16 April 1965, and 1 June 1974, particularly in support of [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien]/[Vous devez être inscrit et connecté pour voir ce lien] to provide radar early warning and limited airborne control of USAF fighter forces engaging MiG interceptors.^{[Vous devez être inscrit et connecté pour voir ce lien]}

Flying orbits over the [Vous devez être inscrit et connecté pour voir ce lien] and later over [Vous devez être inscrit et connecté pour voir ce lien], they were the forerunners of [Vous devez être inscrit et connecté pour voir ce lien]
aircraft.

The U.S. Navy used a variant,the NC-121 in their Blue Eagle unit from 1965–1972.

The Blue Eagles were radar jamming and radio broadcast airplanes.

The Blue Eagles were based in Patuxent River MD and were part of oceangraphic squadron VXN-8.

Big Eye

At the onset of Rolling Thunder, the North Vietnamese had an advantage in that their radar coverage could detect most US strike aircraft flying at 5000 feet or above virtually anywhere in the country, using a system that was difficult to jam.

US forces countered with radar ships ("Crown") in the Gulf of Tonkin and a ground site at [Vous devez être inscrit et connecté pour voir ce lien], [Vous devez être inscrit et connecté pour voir ce lien], but both systems were [Vous devez être inscrit et connecté pour voir ce lien] and had serious gaps in coverage.

To increase coverage the [Vous devez être inscrit et connecté pour voir ce lien] (7 AF) requested airborne radar support and the [Vous devez être inscrit et connecté pour voir ce lien] (redesignated [Vous devez être inscrit et connecté pour voir ce lien] in 1968) was directed to set up the Big Eye Task Force.

Five EC-121Ds and 100 support personnel of the 552nd Airborne Early Warning and Control Wing at [Vous devez être inscrit et connecté pour voir ce lien], California, were deployed to Tainan Air Station, [Vous devez être inscrit et connecté pour voir ce lien], with four of the EC-121s sent on to a forward operating location at [Vous devez être inscrit et connecté pour voir ce lien], near [Vous devez être inscrit et connecté pour voir ce lien], [Vous devez être inscrit et connecté pour voir ce lien].

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The EC-121s were designed for detection of aircraft flying over water, and ground clutter (spurious signal returns off of terrain features such as mountains) caused interference with their radar pictures.

Their crews, however, were experienced in tracking [Vous devez être inscrit et connecté pour voir ce lien] aircraft over Cuba and had developed a technique whereby an EC-121 flying at 50 to 300 feet could bounce a signal from its bottom-mounted APS-95 Search radar off the surface of the water and detect aircraft at medium altitudes out to 150 miles.

Operating in pairs, one Big Eye EC-121 flew a 50-mile [Vous devez être inscrit et connecté pour voir ce lien] pattern approximately 30 miles offshore (the Alpha orbit), with the orbit's center at [Vous devez être inscrit et connecté pour voir cette image][Vous devez être inscrit et connecté pour voir ce lien].

The second flew a track at 10,000 ft (the Bravo orbit) farther from the coast, acting as a spare for the Alpha EC-121.

This provided a practical detection range of 100 miles, just enough to cover the [Vous devez être inscrit et connecté pour voir ce lien] urban area and the main MiG base at Phuc Yen.

A major disadvantage of this arrangement, however, was that most MiG contacts were beyond the 70-mile range of the Big Eye's APS-45 Height Finder radar, so that they were unable to provide this crucial data to USAF strike forces.

Furthermore, technical shortcomings in the EC-121D's systems precluded either controlling a fighter intercept or identifying a specific flight under attack.

The missions from Tan Son Nhut began 21 April 1965, using the call signs Ethan Alpha and Ethan Bravo, which became standard.

After refueling at [Vous devez être inscrit et connecté pour voir ce lien] Air Base, Ethan Alpha made a wave-top approach to its orbit station, where it remained five hours.

Because of the threat of MiG interception, EC-121s were protected by a [Vous devez être inscrit et connecté pour voir ce lien] of [Vous devez être inscrit et connecté pour voir ce lien], and if for any reason the MiGCAP could not rendezvous, the EC-121s cancelled their mission.

Air conditioning systems aboard the EC-121 were virtually useless in this profile and the heat produced by the
electronics, combined with the threat of being shot down, made Alpha orbit missions in particular highly stressful.
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On 10 July 1965, in its first airborne-controlled interception, an EC-121 provided warning to a pair of US [Vous devez être inscrit et connecté pour voir ce lien] fighters, resulting in the shooting down of two MiG-17s.

The Big Eye Task Force remained at Tan Son Nhut until February 1967, when the threat of [Vous devez être inscrit et connecté pour voir ce lien] ground attacks prompted a move to [Vous devez être inscrit et connecté pour voir ce lien].

College Eye

On 1 March 1967, Big Eye was renamed College Eye Task Force and relocated at [Vous devez être inscrit et connecté pour voir ce lien].

Because of the complexity of the aircraft and its systems along with the large support group it required, the CETF was not a welcome tenant at the relatively small Thai bases.

It moved to [Vous devez être inscrit et connecté pour voir ce lien] in July and to its final station at [Vous devez être inscrit et connecté pour voir ce lien] on 17 October 1967.

From April 1965 to early 1966 and beginning again in late 1967, the EC-121Ds also controlled a flight of MiGCAP fighters for unarmed support aircraft operating over the Gulf.

The EC-121Ds also served as an airborne communications relay center for strike aircraft to transmit mission results and position reports to the control center at Da Nang; directed operations of fighter escorts, MiGCAPs, [Vous devez être inscrit et connecté pour voir ce lien] flare ships, and [Vous devez être inscrit et connecté pour voir ce lien] strike aircraft along the North Vietnamese-Laotian border; provided radar and navigational assistance for [Vous devez être inscrit et connecté pour voir ce lien] missions; and assisted fighters in finding [Vous devez être inscrit et connecté pour voir ce lien] for emergency refueling.

The government of China on 12 May 1966, formally protested an [Vous devez être inscrit et connecté pour voir ce lien] by an [Vous devez être inscrit et connecté pour voir ce lien] pursuing a North Vietnamese MiG it subsequently shot down 25 miles inside Chinese territory.

A US board of inquiry recommended that College Eye also monitor the "[Vous devez être inscrit et connecté pour voir ce lien]" inside the North Vietnamese border with China, provide alerts to US aircraft nearing the buffer zone, and report border crossing violations by US aircraft. This could not be done from the Gulf and a third orbit, called Ethan Charlie, was created in Laos. After tests in June and August, regular missions began 24 August.

There were not enough EC-121s or crews to support three orbits twice daily, so the Laotian orbit was only flown every third day, with Ethan Bravo missions canceled on those days.

After 13 October 1966, the Charlie orbit was flown every day and the Bravo orbit suspended altogether.

In April 1967, four more EC-121s were deployed, two to Thailand on 29 May, making for a total strength of three College
Eyes in Taiwan and six in Thailand.[Vous devez être inscrit et connecté pour voir ce lien]

In April 1967, the Air Force began fitting its entire EC-121 fleet with the QRC-248 [Vous devez être inscrit et connecté pour voir ce lien] interrogator.

The QRC-248 had been developed to surveil Soviet-[Vous devez être inscrit et connecté pour voir ce lien] aircraft flown by the [Vous devez être inscrit et connecté pour voir ce lien].

The SRO-2 transponders installed in Soviet export MiGs enabled Cuban [Vous devez être inscrit et connecté pour voir ce lien] radars to identify and control their fighters.

A testbed EC-121 called Quick Look had flown with College Eye in January 1967 to test the QRC-248 and found that North Vietnamese MiGs used the same transponder.

QRC-248 accurately discriminated MiG radar returns from the myriad returns picked up during a mission, and extended the range of low-altitude detection to more than 175 miles, covering virtually all important North Vietnamese target areas.

By 31 May, all College Eyes had been fitted with QRC-248.

The mission of the Bravo orbit was changed from that of a backup for the Alpha orbit to being the primary QRC-248 listener.

However College Eye was prohibited by the [Vous devez être inscrit et connecté pour voir ce lien] from actively "interrogating" MiG transponders, following a [Vous devez être inscrit et connecté pour voir ce lien] security policy protecting its "intelligence sources" (of which the QRC-248 was one), and thus was restricted to waiting for North Vietnamese GCI to interrogate its aircraft.

QRC-248 began regular use on 21 July 1967, but by then North Vietnam's MiG force, which had suffered serious losses in May, had suspended combat operations.

In the last week of August, however, after a period of intensive training and revision of tactics, the MiGs began to engage US strike forces again, scoring a number of kills.

Seventh Air Force finally obtained permission for the Bravo orbit EC-121 to actively interrogate with the QRC-248 on 6 October. By 4 December, its success outweighed any value in flying the Alpha orbit, which was discontinued.

On 1 March 1968, the College Eye call signs were changed to Ethan 01, 02, 03, and 04 in conformity with standard Air Force procedures.

Ethan 03 (the Laotian orbit) began "positive control" (airborne direction) of C-130 [Vous devez être inscrit et connecté pour voir ce lien] ship flights and A-26 Invader night interdiction missions along the [Vous devez être inscrit et connecté pour voir ce lien] in [Vous devez être inscrit et connecté pour voir ce lien] on 19 April 1968.

The task force was scaled back on 1 July 1968, to four EC-121Ds and the Rivet Top testbed aircraft to allow for the basing of another College Eye detachment at [Vous devez être inscrit et connecté pour voir ce lien], Japan.
The name of the task force was discontinued on 30 October 1968, when it was redesignated a final time as Detachment 1 (Rotational), 552nd AEWCW.

The EC-121 deployments to Southeast Asia were discontinued in June 1970 in the expectation that they would no longer be utilized.

Rivet Top

On 9 August 1967, while the College Eye Task Force was still based at Udon, another prototype EC-121 variation began operations testing new equipment as Detachment 2 of the Tactical Air Warfare Center.

Known as Rivet Top, this modified EC-121K (later re-designated EC-121M) carried the QRC-248 newly installed in the College Eye aircraft, but also had electronic interrogators capable of reading two additional Soviet transponders, the
SRO-1 and SOD-57.

Its electronics were custom-built rather than off-the-shelf.
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However its most important upgrade was the highly secret "Rivet Gym" installation.

This consisted of the addition to the crew of Vietnamese-speaking intelligence specialists who manned four voice
communication intercept stations able to monitor all communications between the MiGs and their GCI controllers.

Despite this advantage, the Rivet Top experienced two problems which reduced its effectiveness.

Its listeners did not have radar scopes to correlate intercepted conversations with specific flights of MiGs, and thus could not determine which US aircraft might be under attack.

Secondly, like QRC-248, Rivet Gym was a Signal Intelligence ("[Vous devez être inscrit et connecté pour voir ce lien]") asset of NSA, and subject to even more stringent rules protecting knowledge of its existence.

Even when real-time warnings to US aircraft were finally permitted in mid-1972, fighter crews were not made aware of
the source of the warnings and because EC-121 radio communications were so poor, mandating the use of a radio relay aircraft that often failed, they tended to disregard the credibility of the source.

The Rivet Top prototype moved to Korat along with the College Eye Task Force in October 1967.

Originally scheduled to return to the United States in February 1968, because of its value it remained at Korat until 1969.

Flying daily missions through its testing period, it began flying every-other-day missions over the Gulf of Tonkin after 31 March 1968, when Rolling Thunder operations were sharply scaled back.

Rivet Gym installations were back-fitted to all College Eye EC-121s by the end of May 1968.

Operation Kingpin

Two EC-121Ds, newly-modified with the Southeast Asia Operational Requirement 62 (SEAOR-62) electronics suite but not yet operational as EC-121Ts, were ordered to Korat on 29 October 1970.

Under the guise of being field tested, they were accompanied by a C-121G carrying 52 crew members, the most experienced technicians of the 552nd AEWCW, and equipment necessary to maintain the new electronics suite.

The SEAOR-62 package was supported by a digital data receiver ground terminal and by radio relay equipment transshipped by separate classified airlift.

The EC-121Ts arrived in Thailand from McClellan Air Force Base on 12 November.

The purpose of the deployment was to provide an integrated tactical data display with real-time inputs (similar to the Navy [Vous devez être inscrit et connecté pour voir ce lien] equipping [Vous devez être inscrit et connecté pour voir ce lien] platforms of [Vous devez être inscrit et connecté pour voir ce lien]) in support of [Vous devez être inscrit et connecté pour voir ce lien], a [Vous devez être inscrit et connecté pour voir ce lien] mission to rescue prisoners at [Vous devez être inscrit et connecté pour voir ce lien] prison.
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Once at Korat, some equipment was tested for the first time because of emission restrictions in U.S. airspace, and the only available manuals and checklists were notes from early flight tests. Even so, both aircraft were operational by 17 November.

On 20 November 1970, at 22:00 and 22:10, the two Warning Stars, using the call signs Frog 01 and Frog 02 respectively, took off from Korat and took station at the previously established low altitude Alpha orbit over the Gulf of Tonkin, with Frog 02 as a backup standby.

The 17-man crews were advised in the air of the nature of the rescue mission and their role to provide MiG warning and
to direct Air Force F-4 Phantom CAP intercepts.

As Frog 01 began its climb to the higher Bravo orbit, it experienced a ruptured oil line that forced the shutdown of one engine. As planned, Frog 02 became the primary aircraft when Frog 01 made an emergency landing at Danang.

The new equipment failed to function properly aboard Frog 02.

The ground receivers at the Kingpin command post in Danang failed to receive data, and the [Vous devez être inscrit et connecté pour voir ce lien] processors would not display aboard the aircraft, despite repeated repairs.

Their own radar monitors experienced excessive electronic noise, and the jamming of North Vietnamese radars by nearby [Vous devez être inscrit et connecté pour voir ce lien] hindered efforts of the radar technicians to correct the problems.

While unable to provide [Vous devez être inscrit et connecté pour voir ce lien] information to the F-4s escorting the mission, Frog 02 remained on station and relied on its Rivet Top capability to provide supplementary data.