Fort Huachuca, AZ. - Airborne Radio Direction Finding (ARDF) proved its value to US combatant commanders with the success of Operation STARLIGHT in August 1965. However, the Army had been utilizing direction-finding (DF) capabilities to locate enemy transmitters since as early as World War I. The concept was simple: upon acquiring a radio signal, DF stations within an established DF net would simultaneously take bearings on the transmission. The point where three or more lines crossed would result in a "fix." When the Army Security Agency's (ASA) 3d Radio Research Unit (RRU) arrived in Vietnam in 1961, they fully expected to follow the same process. The plan was set up a DF net at semi-permanent sites and pass targeting locations to mobile DF teams using AN/PRD-1s. The mobile teams would be able to get as close as five to fifteen miles from the enemy transmitters and produce the necessary fixes.
However the Vietnam War was different, presenting numerous challenges to traditional approaches. It was a war that had no fronts; the enemy's forces were dispersed. Operating from sanctuaries in Laos or Cambodia, or from secluded base areas, the enemy attacked selected targets of his own choosing, avoiding Allied sweep operations by dispersing again after an attack. In addition, the types of communications equipment the insurgents used produced signals that were harder to intercept; the high humidity had negative effects on the DF equipment; and the lack of transportation to remote sites all necessitated a different plan. One of the considerations ASA's leaders came up with was an airborne DF system.
Airborne DF had never been tried before. The challenges were many, from creating an airborne system that could discriminate between direct waves and sky waves to choosing the right kind of aircraft for the mission. However, by the spring of 1962, a year after their arrival in Vietnam, the 3d RRU was finally able to provide significantly better signals intelligence (SIGINT) support to the South Vietnamese Army with ASA's fledgling ARDF capability. The ARDF operator could get closer to the target transmitter without putting himself in imminent danger; one aircraft could move fast enough and cover enough area to eliminate the need for a network of DF teams; the response to the tactical commander's requirements was faster than with ground DF equipment; and most importantly, the ARDF was more accurate. It could precisely target the enemy's location, which led to follow-up by artillery, air strikes, and ground operations by South Vietnamese forces.
1965 marked the arrival of the first US combat troops into Vietnam, leading to new demands for ARDF support. Army Security Agency had a total of 30 aircraft on hand, under the 3d RRU's command and control. In August, several battalions of US Marines had been sent into Vietnam, and the 1st Viet Cong Regiment was organizing an attack against the large Marine base at Chu Lai. Marine intelligence was aware of a potential attack, between rumors and agent reports. The latest reports, however, listed the main body of the Viet Cong regiment as being 30 to 40 miles away. Until, on August 15, an ARDF report placed the enemy on the Van Tuong Peninsula, just a few miles from Chu Lai. If this was true, the enemy was in an extremely vulnerable tactical position, and the Marines had an opportunity to trap a very large force.
The commander of the 3d RRU published an intelligence report, which was briefed to General Joseph McChristian, the Chief of Intelligence on the MACV (Military Assistance Command -- Vietnam) staff. The next day, General McChristian contacted the Marine Commander, Lieutenant General Lewis Walt, who launched a combined air-sea-land attack against the 1st VC Regiment. The Marines met heavy resistance, but the enemy's losses were much higher. Operation Starlight was considered a major success and the first major US victory over the Viet Cong. It was also the first successful application of close tactical ARDF support. The 3d RRU platforms were able to provide continuous fixes on the terminals of the enemy forces. This information, which reflected enemy locations and movements, was passed through the 8th RRU to the 3d Marine Division, allowing the Marines to make real-time adjustments and bring unrelenting pressure on the enemy.
It was a huge breakthrough for airborne SIGINT assets. Lt. Gen. Walt said, "The intelligence produced by your units was a clinching factor in the decision to launch this operation. Subsequent events confirmed the accuracy and timeliness of the intelligence." General McChristian called the SIGINT "the confirming catalyst which led to our decision to act." The success of Operation Starlight led to the procurement of 41 additional aircraft for ARDF, and the creation of the ARDF Coordination Center to manage Air Force and Army ARDF missions. ASA would continue to expand and improve its ARDF assets, providing direction-finding support through multiple airborne platforms throughout the remainder of the Vietnam War.
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