Linebacker I

June 1, 2012

Forty years ago, the nation relied on airpower to halt North Vietnam’s biggest conventional invasion of the Vietnam War. This was Linebacker I.

At the time, few expected such a test. It was 1972, the year the US got out of Vietnam and handed off defense to South Vietnamese forces. From a peak of more than 500,000 forces in country in 1968, the US had reduced troops to 156,000 by January 1972, pulling 179,000 in 1971 alone. Plans called for dropping to 67,000 by July.

(USAF photo)

President Richard M. Nixon called the policy “Vietnamization.” Behind the scenes his Administration conducted peace talks in Paris aimed at getting both the US and the North out of South Vietnam and leaving the country intact. Part of the deal was a pledge to return with air and naval power if needed.

America’s grand strategy was changing, too, and geopolitical shifts would figure in the timing of the North Vietnamese attack. Nixon visited China from Feb. 21 to 28, 1972, and the famous Moscow Summit that for a time melted the Cold War into déténte was scheduled for May 1972.

Hanoi took note. The North had not achieved its goal of unifying Vietnam under a communist government. Superpower rapprochement threatened the support for the regime. A successful attack to split South Vietnam would upend the situation and put Hanoi in a much more powerful position. The so-called Easter Offensive launched on March 30, 1972.

The invasion was not spontaneous. Gen. Vo Nguyen Giap had rearmed the North in the years since the failed Tet Offensive of 1968. A force of three divisions, with about 30,000 men and 200 Soviet T-54 tanks, crossed the demilitarized zone. Within a few days, attacks began along three fronts, mounted from over the border in Laos. The plan called for a rapid victory to split South Vietnam into three parts and give the North control of Saigon, capital of the South.

“The North Vietnamese knew from their experience that they could not win at the conference table what they had not gained on the battlefield,” wrote Nguyen Tien Hung and Jerrold L. Schecter in the 1986 book The Palace File.

Giap wanted to take advantage of the drawdown of American forces. Giap also doubted that his southern opponents—known as the Army of the Republic of Vietnam (ARVN)—would provide strong resistance, given their recent poor performance in an aborted invasion of Laos. Whatever gains Giap’s forces made would be useful bargaining chips.

“The crucial factor that finally tipped the balance was President Nixon’s visit to Peking, which made the Politburo in Hanoi doubt that China would continue to support them as it had before,” Giap’s biographer Peter G. MacDonald confirmed.

Expeditionary Airpower

To counter Giap’s initiative, the first task was to move fighters back into theater as fast as possible. Contingency plans called for bringing in Air Force, Navy, and Marine Corps aircraft to augment the South Vietnamese defenders. But the plan was untried.

Nobody knew whether airpower could swing back into a theater in time to deny enemy objectives.

“If anybody had told me … that you could take a fighter wing out of Holloman Air Force Base, New Mexico, and have it overseas in less than a week and have it flying in combat, I’d have said, ‘You’re nuts!’ ” said Gen. Lucius D. Clay Jr., who was commander of Pacific Air Forces during Linebacker I.

The USAF rapid deployment was dubbed Constant Guard. In actions during phase one, beginning April 5, 38 C-141 flights in a 72-hour period brought personnel and cargo into Thailand. F-105s from McConnell AFB, Kan., flew to Korat AB, Thailand.

The first wave of 18 F-4Es from Seymour Johnson AFB, N.C., arrived on April 11, and another 18 followed a day later. Phase two of Constant Guard dispatched another 36 F-4s from Homestead AFB, Fla., and Eglin AFB, Fla., in the first week of May.

An F-111 prepares to depart for Takhli AB, Thailand, in 1972 to support Linebacker. (Photo via the National Archives)

In Constant Guard III, 72 F-4s were sent from Holloman to Takhli AB, Thailand.

Bombers responded, too. In Strategic Air Command’s Bullet Shot operations, some 120 B-52s deployed to Guam and Thailand between April and June. Tankers in theater rose from 30 to 114. Between April 1 and May 24 the number of strike aircraft the US Air Force had available for operations in Southeast Asia went from 375 to 625; by the end of July, it was nearly 900, noted historian Eduard Mark.

“I think this exercise has really proved that the Air Force has grown with the times. It shows our flexibility to go anywhere in the world and do the job assigned,” Clay noted.

The Marines and Navy also rushed forces to the theater. Three squadrons of Marine F-4s deployed to Da Nang in South Vietnam in early April. The Navy had two carriers on station when the offensive began. Three more arrived in early April, a fifth received orders to deploy to Southeast Asia, and a sixth came on April 30.

Giap’s Plan of Attack

Meanwhile, the three-pronged attack was unfolding.

  • Military Region I: The Easter Offensive began here with a thrust by two divisions and three regiments toward Quang Tri. Another division attacked from the west, toward Hue. In this region, ARVN troops retreated, until a new military commander rallied the defenses. The crucial point became the defense of the My Chanh river.
    • Military Region II: On April 1, 1972, North Vietnamese forces attacked in the central highlands, toward Kontum and Pleiku. The showdown came with the defense of Kontum.
        Military Region III: The attack in MR III was pointed toward potential capture of Saigon. On April 2, the North Vietnamese struck toward the main road to Saigon. They took initial objectives, and then heavy fighting concentrated around the town of An Loc.

      In all regions, Giap counted on a few significant advantages. One was the use of dry roads to supply forces via Laos. April promised low ceilings—to shield forces from tactical aircraft. The offensive was also the first to employ Soviet tanks in great numbers. According to Giap’s biographer, the new factor giving him hope for a breakthrough was availability of Russian T-54 and T-72 tanks.

      It was not to be. Linebacker I, as it was eventually called, “would halt the invasion and so devastate North Vietnam’s military capabilities that Hanoi would be compelled to negotiate seriously for the first time since peace talks began in 1968,” wrote historian Earl H. Tilford Jr. in his book Setup.

      As the new wealth of expeditionary airpower flowed back to Thailand’s bases, Washington widened the war. In 1968, President Lyndon B. Johnson had stopped bombing the North on the condition that North Vietnamese forces did not attack below the DMZ. Giap’s invasion broke the agreement.

      On April 2, US aircraft were authorized to bomb the North for the first time since 1968. Nixon told his advisors on April 4: “Let’s get that weather cleared up. The bastards have never been bombed like they’re going to be bombed this time, but you’ve got to have [the] weather.”

      (Staff map by Zaur Eylanbekov)

      Operation Freedom Train from April 6 to May 9 attempted to interdict supplies and railyards supporting Giap’s offensive. On May 1, 1972, after a fruitless meeting with North Vietnamese diplomats, Nixon upped the ante again, deciding to break the invasion.

      Nixon expanded the operation and gave it the new code name Linebacker. He was determined “to go for broke,” he told his National Security Advisor Henry A. Kissinger.

      US aircraft could now attack nearly anywhere across North Vietnam. Authorization for attacks on Hanoi and the mining of Haiphong Harbor came on May 8. At the same time, Nixon reiterated a 1971 proposal for a cease-fire.

      But pressure on the North was not the only point. Battlefield airpower was a mainstay, providing fires support to ground forces and resupplying the besieged garrison at An Loc in Military Region III. Despite all the power brought to bear on Hanoi and Haiphong, the South Vietnamese had to hold their ground, Nixon noted.

      Air control and coordination were the first tasks. In Military Region I, the air environment could be difficult: The North had moved SA-2s into the region. On Feb. 17, North Vietnam fired 81 SA-2s, taking out three F-4s. In April, fliers reported the SA-7 operational in the South. These SAMs would eventually claim several forward air controllers (FACs) and attack aircraft.

      On the ground, the campaign demanded close work between US advisors, airmen, and their South Vietnamese counterparts.

      “By 1972, there were very few US ALOs [air liaison officers] still in theater,” wrote USAF Lt. Col. Matthew C. Brand in a 2007 master’s thesis for the US Army Command and General Staff College. Hence most of the terminal air control was provided by airborne FACs, or FAC-As.

      Could US airpower halt the attack in Military Region I? For weeks the battle hung in the balance. Forces crossed the DMZ, moving south, and also attacked to the east, past the former firebase at Khe Sanh. The objective was the ancient city of Hue. Between the North and Hue lay the towns of Dong Ha and Quang Tri, along a rail and road line leading directly to Hue.

      At one point, Giap’s forces overran 12 fire-control bases, leaving only US Navy surface gunfire and joint aircraft to support defenders. The offensive resumed on April 27, in bad weather. Dong Ha fell the next day and on April 29, four North Vietnamese divisions, about 40,000 men, advanced on Quang Tri.

      In a night action, US Army’s 18th Cavalry vehicles held a bridge on the north side of the city, while air strikes destroyed all five enemy tanks attacking the bridge. Then on May 1, the ARVN evacuated Quang Tri, leaving equipment strewn along the road to Hue.

      After the debacle at Quang Tri, a new ARVN commander took over. Lt. Gen. Ngo Quang Truong used the first week of May to set up a new defensive line at the My Chanh river, south of Quang Tri, a third of the distance to Hue. Truong also called for air interdiction against North Vietnamese forces pressing toward Hue. Truong tasked air to hit 130 mm artillery, tanks, smaller artillery, and trucks. In three days, fighters dropped 45 bridges between the DMZ and Truong’s line at the My Chanh.

      A USAF SAM hunter-killer group including two F-4Es and three F-105Gs takes turns refueling from a KC-135 during a Linebacker mission. (USAF photo)

      The new tactic of attacking tanks with laser guided bombs helped hold the line. One FAC watched in amazement as the two F-4s he called lased and plinked a T-54 and a PT-76 a mile from the town of My Chanh. Attack aircraft, fighters, and gunships tallied more than 70 percent of the tanks hit in Vietnam in April and May 1972.

      By May 13, Truong’s forces were making limited counterattacks. B-52s and fighters struck ahead of the advancing ground forces. The turning point came between May 20 and May 29, 1972. The North launched a final offensive, crossing the My Chanh in several places. But with air support, Truong’s outnumbered defenders held the line. Tactical air destroyed 18 tanks. The last North Vietnamese forces retreated back across the My Chanh on May 29.

      The battle for MR I was an air campaign in itself. Some 18,000 sorties were flown in MR I from April through June 1972. In late June, Truong’s forces shifted to the attack, heading north to retake Quang Tri. The strongest of Giap’s offensive drives had been halted and turned back.

      Military Regions II and III

      The attacks in Military Regions II and III relied just as heavily on airpower in many forms. In Military Region II, Giap’s objectives included the city of Pleiku, scene of fighting much earlier in the war.

      Giap’s forces again made early gains, including the capture of a vital airfield at Dak To. South Vietnamese forces fell back to make a stand in the city of Kontum.

      North Vietnamese forces cut Highway 14 north of Pleiku on April 24, leaving “the defenders of Kontum wholly isolated except by air during more than two months of heavy and close fighting,” wrote the authors of a USAF monograph, “Airpower and the 1972 Spring Invasion.”

      C-130s and South Vietnamese Air Force aircraft delivered fuel, ammunition, and rice. Night operations helped, but several C-123s and other aircraft were lost at Kontum airfield due to enemy fire. In late May and June, airdrop became the primary means of resupply.

      Air also became the only source of mobile long-range offensive firepower for the defenders. Helicopter gunships and tactical aircraft helped break up a major attack on May 14. Army helicopters eventually claimed 11 T-54 kills around Kontum with tube launched, optically tracked, wire guided (TOW) missiles, while USAF crews claimed 15 tank kills through May 18.

      On May 26, Kontum came under heavy shelling, closing the airstrip. B-52s, fixed wing gunships, and tactical air counterattacked. In May alone, the B-52s flew nearly 1,000 sorties in MR II. PACAF concluded “the effect of air on the daily ground situation had been significant,” according to the USAF monograph. Air helped the defenders hold Kontum, counterattacked enemy concentrations, and denied the ability to gain additional territory.

      The defense of An Loc—just 60 miles from Saigon—dominated the battle in Military Region III. Some 20,000 military and civilian personnel were trapped there. With Giap’s forces holding Highway 13 south of the city, An Loc was cut off.

      In the first two weeks of April, tactical aircraft flew 2,500 sorties in MR III, mostly around Loc Ninh, which fell, and An Loc, which held. Now An Loc emerged as the key to preventing Giap’s forces from pushing down Highway 13 to Saigon.

      B-52s conducted close air support. According to the USAF monograph, Army Brig. Gen. John R. McGiffert III described the B-52s as “the most effective weapon we have been able to muster.” He explained that the threat of heavy bombers forced the enemy to break up into smaller units, and when they massed they paid a terrible toll.

      Gunships worked with US Army advisors to target buildings and streets with precise, heavy fire and to attack North Vietnamese troops penetrating the city. During the battle, the garrison of ARVN defenders and their American advisors, including two Ranger battalions, relied on air-dropped supplies.

      The last North Vietnamese troops were driven out of An Loc on June 12 and the siege lifted on June 18. By the end of June 1972, ARVN forces had returned to the offensive in all three military regions. Giap’s plan had failed.

      “Tactical air support was directly instrumental in each of the three main campaigns within South Vietnam, first blunting and then breaking the communist momentum,” concluded the USAF monograph.

      An Air Force Historical Studies Office fact sheet summed up the operational outcome: “Nixon’s use of airpower to disrupt supply lines and kill the enemy on the battlefield stopped the offensive and helped drive the enemy back a short distance without a reintroduction of the ground forces he had withdrawn from the South.” Only 43,000 American airmen and support personnel remained by the time of the offensive.

      Linebacker’s airpower halted the invasion.

      Lessons of Linebacker I

      Gen. Lucius Clay Jr., commander of Pacific Air Forces during Linebacker I. (USAF photo)

      Linebacker was a breakthrough in advanced air attack technology and in the overall control of the campaign.

      US Air Force and Navy aircraft had considerable success against mobile North Vietnamese forces, including tanks. At critical battles such as the siege of An Loc, gunships, attack helicopters, fighters, and B-52s all destroyed tanks on the move.

      While political oversight was tight, Nixon’s guidelines made airpower more effective by removing many of the operational restraints that dogged Rolling Thunder years before.

      An Air Force report found, “The prevailing authority to strike almost any valid military target during Linebacker was in sharp contrast to the extensive and vacillating restrictions in existence during Rolling Thunder” operations, the 1965-1968 campaign over North Vietnam. Attacks pushed to within 30 miles of the Chinese border, and later to just 15 miles. Only a few areas and targets in Hanoi remained off limits in Linebacker I.

      Nixon and aides approved a master target list then left decisions on strikes to theater commanders.

      Linebacker I clearly also benefited from the North’s shift to sustained ground combat with large mechanized forces. This required a much greater logistical effort than guerilla warfare and opened up the supply lines to aerial interdiction.

      The sheer weight of US airpower made the biggest impression.

      In fact, Linebacker I planted the seeds of success in future campaigns and became the template for the strategy of swinging airpower to halt and deny enemy ground force objectives. That strategy remains at the center of US policy in 2012.

      Giap himself summed it up best. Although he would eventually capture the South in 1975, he gave grudging acknowledgement to the role of airpower in battles.

      “The American Air Force is a very powerful air force,” he told an interviewer 10 years after the battle. “Naturally, that air force had an influence on the battlefield. It was a great trump card.”

      Rebecca Grant is president of IRIS Independent Research. Her most recent articles for Air Force Magazine were “Refueling the RPAs” and “Stacked Up Over Anaconda” in the March issue.