MUCKING IT UP ON THE HO CHI MINH TRAIL

BY JOHN PRADOS

By 1966 the American air war in Vietnam, Cambodia, and Laos was well and truly engaged. The United States had set the parameters and standards for the operations, and the basing and logistical underpinnings of the campaign were in place. Goals were still under discussion — and would never be fully agreed upon — but some objectives were widely accepted.

One of these was the idea of cutting off Viet Cong units fighting in South Vietnam from their northern brethren. This was to be accomplished principally by cutting the Ho Chi Minh Trail, a feat that turned out to be a lot tougher than anticipated. One of the most eyebrow-raising schemes to achieve that mission involved modifying the weather. What follows are the stories of Project Popeye and Operation Commando Lava, the attempts to apply science in fighting the Vietnam War.

Geography defined the nature of the war. Even beyond the battlefield, North Vietnamese Army regulars and Viet Cong guerrillas depended upon the land. There was food production, of course, but most critical were the weapons and ammunition needed to fight the Americans and South Vietnamese. Much of the first-rate equipment and supplies had to come from the North.

The long Indochinese peninsula is bisected, north to south, by the Annamite Mountains, which contain only a few passes. On the Laotian side of the mountains a network of trails wound west and south toward enemy base areas that became supply dumps fueling the communist forces. Americans knew this system as the Ho Chi Minh Trail. The Vietnamese called it the Truong Son Strategic Supply Route.

Coupled with the land, the Southeast Asian climate further complicated the movement of supplies. Vietnam and Laos are dominated by a monsoon cycle. In Laos over the Ho Chi Minh Trail, May to October is the wet season when Southwest Monsoon rains soak the land. The Vietnamese-Laotian border roughly follows the crest line of the Annamites. On the Laotian side, spurred by what’s known as “Lao Wind,” annual rainfall can total up to 160 inches. Further inside Laos the rains average about 100 inches a year. American scientists who hoped to use weather as a weapon wanted to add to that already formidable accumulation of rain.

Rainmaking experiments began in the United States in 1946 when a General Electric Corporation researcher tried seeding clouds with silver iodide. The search for applications included seeding hurricanes to weaken them before hitting land and attempts to relieve droughts by inducing rain. The U.S. Senate held a hearing on cloud seeding in 1956.

Proposals for the military use of the technique followed in the early 1960s. Several were presented at a scientific conference in November 1963. In 1966, the Naval Ordnance Test Station at China Lake, California, became the focal point for U.S. experiments on military weather modification. Leonard Sullivan, the assistant director for Defense Research and Engineering for Southeast Asia, proposed Project Popeye that summer.

In August the Joint Chiefs of Staff opened discussions with Adm. U. S. Grant Sharp, the Pacific Theater commander, who oversaw the air war, and Gen. William Westmoreland, the U.S. commander in Vietnam. Dr. John Foster, the director of Defense Research and Engineering, approved the concept, and Defense Secretary Robert S. McNamara on September 17, 1966, okayed a field test in Vietnam.

Less than a week later Westmoreland ordered the initial phase of the operational evaluation.

An expert team from China Lake came to Vietnam for the tests. Pierre Saint-Amand headed the unit of eight men, with Navy Cmdr. Francis R. Walsh as his military assistant. They were given office space and billeted at the U.S. airbase at Marble Mountain outside Da Nang.

As Popeye coordinator, Saint-Amand handled details. Since “Popeye” was the name of the famed cartoon character, code names for elements of the project were drawn from the cartoon. “Wimpy” stood for an injection fuse; “Olive Oyl” for a type suitable for almost any aircraft; “Bluto” for a photo plane power pack; “Swee’pea” for a signal pistol flare charge; and so on.

Tests were carried out from Udorn, Thailand, the operational base. The China Lake team found that 48 of the initial round of 56 test flights were successful. In December 1966 JCS Chief of Staff Gen. Earle Wheeler came up with an operations plan for rainmaking, along with a logistics workup indicating that materials could be shipped immediately and produced in sufficient quantities. The roads descending from the Annamite Mountain passes were believed to be especially susceptible to rainmaking.

The program appeared to offer significant military impact. But problems arose on the diplomatic side. The U.S. State Department approved Popeye on a provisional basis with the understanding that it would be kept under review and terminated if it became legally or politically controversial. State also wanted the operation to be conducted under existing guidelines for air operations in Laos. The Pentagon considered those conditions a State Department attempt to kill the project.

On February 25, 1967, Gen. Wheeler sent two JCS colleagues and Adm. Sharp a memorandum giving the go ahead for Compatriot. McNamara and President Johnson signed off on the operation. Just as the rainmaking initiative moved into high gear, a new wrinkle came up. The creation of Operation Commando Lava, which dealt with the mud that would be created by the cloud-seeded rains. Lots of water made for flood conditions.

Scientists at Dow Chemical discovered that a mixture of trisodium nitrilotriacetic acid and sodium tripolyphosphate added to the moisture would destabilize the soil, retarding evaporation and making the mud extra-sticky. Those chemicals were already on the commercial market in a laundry detergent called Calgon, which came in tablets. The military version was simply poured into sacks. Stacked on pallets, the sacks were rolled down the ramps of C-130s in flight.

Compatriot cloud seeding began in March 1967. The Calgon destabilization began with an experiment in mid-May carried out by C-130s of the 374th Troop Carrier Wing flying from Thailand. Its 41st Squadron provided aircraft to drop the pallets and its operations officer, Lt. Col. William J. Flaugher, directed the project. Planes loaded their pallets at the CIA’s Air America compound at Ubon. Plans for Commando Lava took longer. The Southeast Asia Coordinating Committee — an ad hoc unit including the U.S. ambassadors to Laos and Thailand, Westmoreland, air and special operations leaders, and representatives of CINCPAC — managed overall strategy for the Vietnam War. The committee met in a regular session at Udorn on May 27.

During the meeting, U.S. Ambassador to Laos William C. Sullivan detailed the plans to destabilize roads on the approaches to the Mu Gia and Ban Karai passes over the Annamites. Sullivan wrote that he believed the program “could prove a far more effective road interdiction device (at least in rainy season) than iron bombs and infinitely less costly.” He went on to say: “Make Mud, Not War!”

The 7th Air Force issued the final plan, Operation Commando Lava II, on June 17. Early in July the Joint Chiefs extended the target zone into North Vietnam, adding targets along the basin of the Song Ca River. The initial mission took place in July.

The first flights hit Road 548 in the A Shau Valley inside South Vietnam, where patrols could survey results on the ground. A second series took place from July 25-29. More attempts followed on August 4-5 and 7. Aerial observation indicated that Calgon in some bags did not disperse.

Cloud seeding and soil destabilization pitted American strategizers against North Vietnamese improvisers. Laying logs across the muddy morass was a common countermeasure and kept the Ho Chi Minh Trail open. Results were most apparent to Americans who flew over Laos.

Fred Locke, for example, a pilot with Marine Medium Helicopter Squadron 265, recalled being prepped for a sortie into Laos, when he was told to be sure to avoid calling air strikes against friendly elephants. The startled pilot asked how he was supposed to distinguish friendly from enemy elephants. The enemy ones, he was told, would have bellies tinged red from the clay mud of The Trail.

“I’ll be doggoned if we didn’t see a whole bunch of elephants and they did” have red bellies, Locke said.

Available records do not disclose what happened to Commando Lava after 1967, but Popeye went on through the end of American participation in the war. Sorties against North Vietnam continued until November 1968, and in Laos through 1972.

Nearly 600 rainmaking flights took place in 1967. Sorties peaked in 1968 with 734. The total number was 2,602, with the last on July 5, 1972, dropping tens of thousands of delivery flares. The program cost some $3.6 million ($32.4 million in 2023 dollars) each year.

Ambassador Sullivan’s plea for mud, not war, produced a lot of misery in the backwoods of Laos, but never closed the Ho Chi Minh Trail. As an isolated measure, in the absence of a comprehensive winning strategy, Popeye didn’t quite make it. Resourceful improvisers, the Vietnamese who worked the Trail countered each of the American technical innovations.

Historian John Prados’s many books include Vietnam: The History of an Unwinnable War. He was a senior fellow with the National Security Archive, heading its Vietnam Documentation Project. A longtime contributor to this magazine, Prados died on November 29, 2022.

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