At the earliest stages of the U.S. buildup in Vietnam, a system was
needed to locate Viet Cong and North Vietnamese radio transmitters.
Conventional ground-based Radio Direction Finding (RDF) methods proved difficult in attempting to locate low-powered enemy transmitters. The
solution was Airborne Radio Direction Finding (ARDF) by Army and Air
The aircraft selected by the Air Force for its ARDF effort was the
venerable C-47. The C-47 was a derivative of the DC-3 commercial
airliner developed by the Douglas Aircraft Company. First built in the
1930’s, the C-47 (Gooney Bird) distinguished itself as a transport in
world War II, the Berlin Airlift, and the Korean War.
Prior to being sent to Southeast Asia, the planes had to be equipped with a multitude of electronic components so as to fulfill their mission. Thus was born the EC-47.
The ARDF area of operation was South Vietnam, Laos (one six miles from the coast of North Vietnam), and later Cambodia. The Air Force ARDF program quickly demonstrated the capability to provide rapid determination of enemy locations and movements. Data was immediately transmitted to the ground where it was used to direct troop movements, artillery fire, tactical air strikes, and B-52 missions.
In 1966 squadrons were formed at Tan Son Nhut Air Base, Nha Trang Air Base, and Pleiku Air Base to conduct EC-47 ARDF operations. The flight crews consisting of the pilots, co-pilots, navigators and flight mechanics were assigned to the 360th, 361st, and 362nd Tactical Electronic Warfare Squadrons, respectively. The mission specialists, consisting of Morse Radio Intercept Operators (Ditty-Bops), linguists, communications analysts, and equipment repairmen were assigned to the 6994th Security Squadron and its detachments.
Later in the war, Nha Trang and Pleiku operations moved to Phu Cat and Da Nang Air Bases, respectively. In 1969 and 1970, EC-47 operations began at Nakhon Phanom and Ubon Royal Thai Air Bases (RTAFB). The last EC-47 mission was flown from Ubon in June, 1974.
During it’s eight years of operations in Southeast Asia, the 6994th made major contributions to building the intelligence picture of the battlefield in Vietnam. Countless commanders relied on Signals
Intelligence (SIGINT) and Airborne Radio Direction Finding reports when developing their battle plans. It has been alleged that 95 percent of the B-52 strikes conducted in Vietnam were based partially or in full on information provided by the 6994th.
One report of the effectiveness of the EC-47 came during a conversation between Gen. William W. Momyer, Commander, 7AF, and Col. Robert G. Williams, Commander 460th TRW, in May 1967. Colonel Williams quoted General Momyer:
“…I want all personnel in this mission to know that the primary and basic source of intelligence in this country comes from COMPASS DART (now COMBAT COUGAR) and I want the
people in these squadrons to know it.”
The 6994th Security Squadron was recognized for its cryptologic excellence in 1969, when it won the Travis Trophy from the National Security Agency
(NSA). The Travis Trophy is presented annually to the Service Cryptologic unit judged to have made the most outstanding contribution
to NSA’s mission during the previous calendar year. In a message to the Commander, USAF Security Service, the Director of NSA stated:
“Information has been brought to my attention relative to an exceptional SIGINT contribution which was made
by personnel of the 330th RR Co, and the 6994th Security Squadron in South Vietnam. It is noted that through the
combined efforts of personnel in these units, timely and very vital intelligence information was made available to tactical commanders which contributed directly to the engagement with elements of the PAVN 325C Division on 10 May 1968. Further and more important, U.S. forces incurred very light casualties because of their knowledge of the situation as derived from SIGINT.”
It was noted that this engagement took place within 800 meters of an ARDF fix made on 6 May 1968. The NSA director continued:
“The efforts of all those involved in the production of SIGINT information which results directly in the saving of U.S. lives is deserving of the highest praise and I take this opportunity to extend my sincere gratitude and recognition for a job well done to those men involved.”