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War over Radio Waves: Signals Intelligence

The RB-47H flew missions early in the air campaign against North Vietnam (an RB-47H is on display in the museum’s Cold War Gallery). It was replaced by the RC-135. (U.S. Air Force photo)

The RB-47H flew missions early in the air campaign against North Vietnam (an RB-47H is on display in the museum’s Cold War Gallery). It was replaced by the RC-135. (U.S. Air Force photo)

RC-135Cs played an important role in gathering electronic intelligence on North Vietnamese air defense systems. It was nicknamed the “Chipmunk” for its large “cheeks.” (U.S. Air Force photo)

RC-135Cs played an important role in gathering electronic intelligence on North Vietnamese air defense systems. It was nicknamed the “Chipmunk” for its large “cheeks.” (U.S. Air Force photo)

Highly-capable RC-135s -- like this RC-135M COMBAT APPLE aircraft -- conducted communications and electronic intelligence. For most of the Southeas Asia War, unarmed RC-135s maintained a continuous, 24-hour orbit near the border of North Vietnam. (U.S. Air Force photo)

Highly-capable RC-135s -- like this RC-135M COMBAT APPLE aircraft -- conducted communications and electronic intelligence. For most of the Southeas Asia War, unarmed RC-135s maintained a continuous, 24-hour orbit near the border of North Vietnam. (U.S. Air Force photo)

Specialized EC-121s -- like this EC-121K RIVET TOP -- listened in on radio calls between MiG fighters and their ground controllers. The EC-121 crew then passed on real-time warnings to U.S. pilots. (U.S. Air Force photo)

Specialized EC-121s -- like this EC-121K RIVET TOP -- listened in on radio calls between MiG fighters and their ground controllers. The EC-121 crew then passed on real-time warnings to U.S. pilots. (U.S. Air Force photo)

The Air Force had two ground-based signals intelligence intercept sites at Danang, South Vietnam -- one at the air base and another, pictured here, on nearby “Monkey Mountain.” (U.S. Air Force photo)

The Air Force had two ground-based signals intelligence intercept sites at Danang, South Vietnam -- one at the air base and another, pictured here, on nearby “Monkey Mountain.” (U.S. Air Force photo)

An EC-47 crew included a pilot, co-pilot, flight engineer and mission specialists. (U.S. Air Force photo)

An EC-47 crew included a pilot, co-pilot, flight engineer and mission specialists. (U.S. Air Force photo)

The linguists and mission specialists who operated the airborne radio direction finding (ARDF) equipment were assigned to the 6994th Security Squadron of the USAF Security Service. (U.S. Air Force photo)

The linguists and mission specialists who operated the airborne radio direction finding (ARDF) equipment were assigned to the 6994th Security Squadron of the USAF Security Service. (U.S. Air Force photo)

The Radar War: Electronics Intelligence
The enemy's air defense system depended heavily on radar signals. Enemy radars detected incoming U.S. aircraft, guided surface-to-air missiles and directed anti-aircraft fire.

Air Force RB-66C, RB-47H and RC-135 crews identified enemy radar locations and recorded their signals. This electronics intelligence (ELINT) information was then used to target radar sites, warn friendly forces and develop countermeasures against enemy defenses.

Listening in on the Enemy: Communications Intelligence
Intercepting enemy radio voice conversations, or COMINT (for communications intelligence), proved to be a rich source of information about the enemy. COMINT aircraft carried sophisticated electronic surveillance equipment and highly-trained technicians and linguists.

Antique Airlines: EC-47 Airborne Radio Direction Finding
Using airborne radio direction finding (ARDF) equipment, EC-47 crews found enemy ground forces through their radio transmissions. Once the location of a radio signal was "fixed," the information was quickly passed on to friendly troops. EC-47 ARDF fixes were used to target an enemy force for air, ground or artillery attack and to save friendly forces from ambush.

EC-47s also carried linguists who listened in on enemy radio voice transmissions (called communications intelligence or COMINT), gathering even greater knowledge about enemy activity.

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