Captain John E. Donovan, an electronic warfare officer, monitored the equipment in his F-100F Super Sabre fighter. It was December 22, 1965, and his plane was part of a strike mission searching out enemy antiaircraft sites. Two days earlier, a similar mission had gone badly, resulting in the loss of a plane and its crew. As the F-100F in which he was flying raced through the skies over North Vietnam, Donovan detected a signal from enemy radar known as a Fan Song. He notified the pilot, Captain Allen T. Lamb, who began maneuvering the plane to help locate the radar. Lamb took the plane down until the signal disappeared and then ascended until they picked it up again, using the mountains and valleys to help them avoid becoming a target themselves. The two men were flying over the southwestern section of the Red River Valley, which was situated northwest of Hanoi.
Streaking around a hill, Lamb took the F-100F up to 4,500 feet and began looking for the radar and its attendant SA-2 surface-to-air missiles (SAMs). He saw the SAM deployed in the middle of what looked like a village. He noted the tips of three missiles bristling out from beneath a thatched hut, which afforded the missile battery good camouflage. Wasting no time, Lamb radioed the accompanying F-105D Thunderchief fighter bombers to follow his lead. The F-100 swooped down on the enemy position and fired rockets to mark the target for the bombing runs. The F-105 strike succeeded in knocking out the battery. Debris from the destroyed SAM site flew 400 feet into the air amid a column of smoke.
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The American aviators had little time to enjoy their triumph. Donovan detected another Fan Song radar. He could tell this one was already well into its attack cycle, detecting what was known as a high-pulse repetition frequency. This meant that the enemy was only about 30 seconds from launching. The operator would double the frequency at this point to provide a sharper radar image. The entire flight turned back toward its base in Thailand, dropping to low altitude to avoid the Fan Song. One victory was enough for the day. The team had successfully proven a new concept of air warfare designed specifically to target the radars that were vital for modern guided missiles to track their targets. The concept, which was code-named Wild Weasel, was coming of age.
As air warfare evolved during the latter half of the 20th century, aircraft had more to worry about than just enemy cannons and machine guns. Advances in rocketry led to powerful new antiaircraft missiles, and developments in electronics greatly increased the capability of radar and guidance systems. The antiaircraft missiles of the World War II-era could barely be counted on to strike a large area target, but by the 1960s much smaller versions could track aircraft in the sky. The pace of progress was accelerating and air forces around the world struggled to counter each new improvement.
In the first months of the Second Indochina War, commonly known as the Vietnam War, American aircraft began to suffer losses from North Vietnamese SAMs, which were supplied by the Soviet Union. The SAMs covered medium-to-high altitudes, up to 60,000 feet in the case of the SA-2. When U.S. aircraft came in at low altitude to avoid the missiles, they were vulnerable to traditional antiaircraft fire. To counter this threat, the U.S. Air Force initiated a program called Wild Weasel. The program became so successful that the name has since been applied to every U.S. Air Force aircraft developed for this sort of mission.
The mission of a Wild Weasel aircraft is to locate enemy antiaircraft radar and either destroy it or target it for attack by other aircraft, usually accompanying ground attack planes. Radar systems send out waves of energy that reflect off targets, such as aircraft, and return to the radar device, allowing radar operators to track and target the aircraft. But these waves can themselves be detected and tracked back to their source, revealing the position of the radar and allowing the hunted to become the hunters. Accomplishing this task requires specialized equipment and weapons not carried by regular aircraft.
The U.S. Air Force began the Wild Weasel program in October 1965, just a few month after the North Vietnamese SAMs, crewed largely by Soviet advisers, began taking their toll of American planes. By early November the basic equipment had been tested and field testing began. Electronic Warfare Officers (EWOs) learned how to operate the electronics and read the displays that would lead them to enemy radar. Those radars not only had to turn on to lock onto a target, but also had to stay on long enough to track it and then home in on it. The test missions were flown against American radar systems that were similar to the Fan Song. EWOs learned that their equipment worked best at medium altitudes flying directly toward the radar beam’s point of origin. Results were poor when flying at low altitude or parallel to the source.
The Wild Weasel proved able to detect the Fan Song radar signals beyond the 17-mile range of the SA-2, but it had to get closer to pinpoint the exact location. Once the signal was detected a device called a panoramic scan receiver gave an initial direction the plane could follow to close the range. As the distance grew shorter the signal grew stronger. The shorter range vector homing and ranging set could then start detecting it. The EWO could compare readings to ensure they were on the proper heading and roughly gauge the distance. With that determination made, the crew could search visually for the SAM position. The field testing ended on November 18 and the crews were sent to Southeast Asia for operational testing. There, they would have three months to figure out how to best take the fight to the SAMs.
The new Wild Weasel F-100F aircraft arrived at Korat, Thailand, along with their crews, mechanics, and support personnel on November 24. They soon began flying missions over North Vietnam. By late December Donovan and Lamb had knocked out their first SAM site, and the program was on its way to becoming a staple of the U.S. Air Force in Vietnam. The U.S. Air Force dubbed the initial missions Iron Hand. The missions were made up of one F-100F and three or four F-105D Thunderchief fighter bombers, affectionately known as Thuds. The Thuds were faster than the older F-100s and therefore had to fly in a weaving formation to avoid passing the slower lead aircraft.
The evaluation period ended in January 1966. While the concept was sound, it was recognized that the F-100F was too obsolete to perform effectively. To replace it, the Air Force tested the two-seat F-105F as a Wild Weasel and the first five planes arrived in Korat in May 1966. Another half dozen aircraft arrived a month later.
While the Air Force was steadily improving its aircraft, the U.S. Navy designed a new weapon to make the risky job of destroying SAM sites easier. The AGM-45 Shrike was a modification of the Sparrow air-to-air missile designed specifically to home on radar. It was the first of a series of antiradiation missiles that would allow the Wild Weasels to engage the SAMs with more than just unguided rockets. It carried a 149-pound warhead that could easily destroy a radar unit such as the Fan Song. To target a particular radar, the Wild Weasel pilot had to fly directly at it until he was close enough for the homing system to work. The initial versions of the Shrike could not do that until they were within range of the SA-2.
Since the Shrike’s rocket motor burned out after 10 seconds, this meant that the missile continued its flight unguided. Still, as long as the missile was aimed accurately it would still detonate within 20 feet of the radar. As a countermeasure, the radar operators would turn their system off, which often threw the missile off track. This was not a complete loss, though, as a switched-off radar was useless for guiding SA-2s.
The first U.S. Air Force use of the Shrike missile occurred on April 18, 1966, when a Wild Weasel used one to target a SON-9 radar that was used to direct the fire of 57mm and 100mm antiaircraft guns. The missile disappeared into some haze before striking the target, but the EWO noted the radar stopped functioning, indicating it had been damaged. Nevertheless, Wild Weasels remained vulnerable to gunfire and enemy fighters. By August 1966 only four of the 11 F-105Fs in Thailand were still operable. Other fighter wings operating the F-105Fs had lost five aircraft with two other damaged beyond repair. In October a half dozen replacements arrived and were split between the various units to allow them all to operate.