Talking Proud Archives --- Military

LS-85, Airmen left out on the limb, a leadership failure

September 10, 2017

By Ed Marek, editor

NVA develops a plan to attack Phathi, LS-85

I wanted to give you some sense of important trends in the military situation in northeastern Laos from 1966 through early 1968. I've said LS-85 was next on the NVA's attack plan following the defeat of the RLA at Nam Bac during January 1968.

I'll now want to step back a bit and address how the NVA planned to attack LS-85. It started planning far before it executed the attack.

I mentioned earlier that in September 1959, the NVA, created Military Specialist Group 959, designed to supervise communist warfare in Laos. It located its headquarters in Gia-Lam outside Hanoi. It also had a forward headquarters at Sam Neua, Laos. I also said Group 959 created a new infantry group, Group 766 and suggested you keep it in mind. So here we go.


Major Wayne M. McDonnell, USA, wrote a thesis for his Master of Military Art and Science for the US Army Command and General Staff College entitled, “The NVA in Laos:1951-73.” He reported that Group 959 "emerged as the supreme authority in Laos while American interests were managed by the US Mission in Vientiane with assistance form Thailand." He wrote 959 held a special conference at Sam Neua (City) in September 1966. The NVA called and led the conference. Representatives from the USSR, Peoples Republic of China (PRC), and Pathet Lao attended. The purpose of this conference was to develop a plan targeted at Phou Pha Thi Mountain, LS-85. The photo shows Pathet Lao with North Vietnamese cadres planning an operation, presented as an example of such combined planning. I m not sure whether the US knew of this planning conference. McDonnell cited a source reference but I have not yet found it.

I am intrigued here by the dates.

The TACAN site at LS-85 was installed in August 1966 and became operational in September 1966. The more advanced TSQ-81 command guidance radar system installation began in summer 1967 and became operational in November 1967. Remember the TSQ-81 was being handled under a very secretive project named “Heavy Green.” Recall the USAF and JCS had begun work to establish a Combat Skyspot ground directed radar station in northern Laos as early as November 1966. Yet the NVA began planning to attack Phou Pha Thi in September 1966. The timing here is curious.

Perhaps the NVA only knew that Vang Pao had taken Phou Pha Thi, the CIA had set up a command center there, and Hmong forces were driving toward Sam Neua City from that location. Or perhaps the NVA got word of the mounting importance of Phou Pha Thi yet to come and added it to the list of reasons why they had to attack it. Or, perhaps "Heavy Green" was not as secret as thought.

Just prior to this meeting in Sam Neua, Walter Rostow, a Special Assistant for National Security Affairs to LBJ, attached a note to the president on August 3, 1966. He attached it to a message sent by Emory Swank, deputy chief of mission, Vientiane, to the State Department. Rostow's note said:

"We often forget there is a significant, secondary, war going on in Laos."

At this point in time, the US was fixated on stopping or delaying traffic on the Ho Chi Minh Trail rather than maintaining a broad Indochina-wide view. Nonetheless, that is a sobering note to give the president in 1966.


For sure the NVA was able to observe the high amount of helicopter traffic going in and out of Phathi, and had to know something was going on up there. This shows a CH-47, having delivered a cart, being unhooked at LS-85. Furthermore, recall Lt. Colonel Farnsworth lamenting that local Laos watched his people install the TS-81 equipment.

McDonnell said the NVA had several concerns:

  • It wanted to impede USAF air attacks against the NVN and Laos. That implies it knew at least about the TACAN at Phou Pha Thi. It’s September 1966 and the TACAN was installed in August - September 1966.
  • The NVA was very concerned about the site’s growth potential, worried, for example, that the US might install surface-to-surface missiles there.
  • The NVA saw Phou Pha Thi Mountain, because of its height, as a crucial element for control of military forces in northern Laos.
  • The NVA wanted to prevent the CIA and Hmong from using it as a staging base.

McDonnell said the Soviets were not enthusiastic about the NVA plan. They felt it would take too long to prepare for such an attack, perhaps three years. The Chinese were also not enthusiastic, saying it could take as long as seven years to prepare. The NVA disagreed, saying they could take the mountain in three months. That’s how important the NVA viewed this mountain, and, frankly, how sassy it was!

The Soviets gave in to the NVA position. The Soviets showed interest in gaining access to the US equipment for intelligence purposes. That angered the Chinese, seeing this operation as a potential problem for China. For example, they were concerned the action would anger the US sufficiently that it would start attacking Chinese road building efforts in northern Laos and even strike at targets in Southern China. The Chinese angrily left the conference.

Pathet Lao troops


Chinese or no Chinese, the NVA continued planning. Initially the NVA decided to use Pathet Lao troops against Phathi to avoid engaging the wrath of the US directed at NVN. Pathet Lao General Khamtay Siphandone was selected to lead the operation. He was the Chief of Staff for the Pathet Lao at the time. As an aside, during the period 1998-2009 he served as the Laotian president. The photo shows him when serving in that office.

The NVA instructed Khamtay to dispatch people to collect intelligence on the area. In mid-1967 General Khamtay explained to the NVA that his people had not been able to gather intelligence good enough to plan and launch an operation against Phou Pha Thi.

That angered the NVA. Group 959 stepped in, told Khamtay to withdraw his forces, and decided to handle the operation themselves. The requirement stood to conduct the operation within three months of a “Go” decision.

In June 1967, Sullivan sent a message to the State Department that opined Lao government forces and the Hmong held considerable advantage on the battlefield as the rainy season arrived and that it might be possible to achieve territorial gains. Rostow told LBJ:

"The rainy season has arrived in Laos, with wholesome results."

CIA echoed this feeling saying Vang Pao had improved his forces' positions through the first part of the rainy season. CIA went so far to say "The successful implementation of (several tactical) options could contribute to permanently changing the tactical balance of power in northern Laos in favor of the Royal Laotian Government."

The CIA assessment also said that after repulsing several enemy attacks, the enemy intention to follow up with attacks on Phou Pha Thi and Na King (LS-36) could not occur. A point to note here is CIA in June 1967, probably earlier, knew the NVA wanted to attack LS-85. The TACAN was operational by this time, but the TSQ-81 had not yet been installed.

But perhaps the most important point was that CIA and the embassy felt good about the situation in northeast Laos in 1967. Recall from the previous section that in late 1967, the NVA essentially set the Pathet Lao aside and committed very large numbers of regular forces to fight in Laos. That coincided with its plans for the Tet Offensive in the RVN in January 1968.

It's now mid-1967 and the NVA has taken over the planned operation against Phathi, saying they could take it within three months. Group 959 tasked Group 766 to mount the operation immediately. It recommended that only a sapper unit be employed to scale the sides of the cliffs on ropes. Infantry would back it up coming at the Hmong defenders from the East.

In October 1967 the NVA sent in a sapper company from the 305 Sapper Command in Hanoi to conduct preliminary reconnaissance of the site. The 305 is more appropriately called the 305 Dac Cong (“Special Task”) Command. It was officially created in 1967, so it was new. It was very much akin to the British Commandos and US Army Rangers of WWII.

A moment on the word “sapper.” Kenneth Conboy felt Westerners did not translate “Dac Cong.” Conboy said use of the word "sapper" is misleading. Instead, the Dac Cong were much more. They were “highly trained special operations teams.”

A detachment of the 305 Dac Cong sapper unit reconnoitered the LS-85 area for a month, into November 1967. On its return, it reported that a conventional attack would not work. It recommended using only sapper forces to scale the cliffs by rope and recommended use of North Vietnamese Air Force (NVAF) units to prepare the positions for the assault.

I have come across what I have found to be a most illuminating document. It is entitled
Tran Tap Kich Vao Khu 'TACAN' tren Nui Pa-thi cuar Phan doi Dac Cong Quan Khu, ngay 11 thang 3 nam 1968. Or, in English, Raid On the "TACAN" Site Atop Phathi Mountain by a Military Region Sapper Team on 11 March 1968. It was written by Major Do Chi Ben, formerly of the NVA and one who participated in the attack preparations and execution. This document is one chapter of a more encompassing book, Military Region 2, Several Battles During the War of Liberation 1945-1975, published by the People's Army of Vietnam Publishing House, Hanoi, 1996. It was translated by Robert J. Destatte during 1997 and 1998. Destatte had served with the Army Security Agency (ASA) in Vietnam, was assigned as a Senior Analyst, Research & Analysis Directorate, Defense Prisoner of War and Missing in Action Office, and also worked in Hanoi attached to the US/POW Office.

For purposes of this document, Destatte only translated it and does not offer any opinions on its credibility. I have read the translation and it struck me as quite credible, and that is the way I will treat it here. I commend Major Do's entire document to you. It's long and quite detailed. If anything, I walked away from this document impressed by the detail of NVA planning for this assault. This was no slip-shod operation.

Major Do Chi Ben reported there was a feeling it might be hard to coordinate the use of sappers within the NVN government, but it was approved. So a decision was made to use sapper units, specifically those assigned to the 305 Sapper Command. They would scale the cliffs, supported by infantry attacking from the East, the least formidable mountain side.

John T. Correll noted:

“US officials did not believe the enemy could climb the cliffs. The fourth side of the mountain was fortified. The assumptions were wrong.”

In his book
A history of the Hmong: From Ancient Times to the Modern Diaspora, Thomas Vang reported:

“In October 1967, two Pathet Lao spies dressed as Buddhist Monks were caught with cameras at the site.” The Hmong caught them and Vang Pao’s people interrogated them according to Jane Hamilton-Merritt in her book
Tragic Mountains: The Hmong, the Americans and the Secret Wars for Laos. It was then that they confessed. As a result, Vang Pao felt the site had been compromised. Hamilton-Merritt said the USAF disagreed and concluded “the suspects were in fact bona fide Buddhist monks.”

North Vietnamese An-2s attack LS-85


On January 12, 1968, a bizarre event occurred. The NVA launched An-2 Colt biplanes such as shown here to attack the site. I have seen multiple renditions of what happened. There are some disparities in the number. McDonnell said three An-2s attacked, and other sources said four were launched but only two overflew LS-85. Most sources seem to say two attacking aircraft is the right number. General Secord in his book said observers near the site saw four An-2s, but two ships broke off and made a bee-line toward LS-85. The men at the site said there were two. The two An-2s dove on the site and made three passes, employing rockets and machine-gun fire. They also "dumped several bombs"


In his book Thomas Vang said they dropped “fifteen 120-mm mortar shells and fired 57-mm rockets at the radar equipment.” Secord agreed the rockets were Soviet-issue 57 mm fired from pods, while the other ordnance was dropped through tubes in the fuselage, armed by the force of air pressure in the wind-stream. This photo shows a North Korean An-2 firing rockets.

I go with two An-2s in the attack, and agree that there were four but two did not attack. They did minor damage to the equipment and buildings. No Americans were killed, There was no serious damage done to any equipment, but four Hmong civilians including two women were killed and two Hmong soldiers wounded.


Secord said an Air America Bell 212 helicopter such as is shown here was in the air on his way to site 85. Capt. Ted Moore was the pilot. Timothy Castle said he was flying ammunition to LS-85 at the time. Castle quotes Moore recollecting the scene:

"On 11 January 1968 a MiG (enemy fighter aircraft) flew over Site 85 and I presume took photographs. The next day it looked like World War I as I witnessed two biplanes (An-2s) attempting to destroy the electronic gear at Site 85. One of the airplanes dropped explosives and the other, which appeared to carry rockets and machine guns, fired at the site."

Moore decided to chase after what were An-2s. His flight mechanic, Glenn Woods, employed his M-2 (Secord said M-16) automatic carbine and fired at the lead Colt while leaning out the side door. He hit that Colt and it crashed into a ridge near the NVN border. The other Colt appears to have been hit by ground fire from LS-85 while lining up for his fourth pass, and limped back toward NVN for about 25 kms but crashed after being hit. Hmong rushed to both the crash sites and there were no survivors. The crews apparently were Vietnamese.

CIA commented, "The Embassy believed the air attack was an attempt to eliminate the radar without resorting to a costly ground attack."

Surprisingly, Air America fired Moore for creating an "international incident." CIA instructed Air America to hire him back, and it did.

Major Secord and others were said to have been astonished the NVA would use such a means as the rickety old An-2 to attack. While on the surface the attack appears to be a trivial attempt, it did convey one salient point. The NVA most certainly were aware of the site and its mission, and were serious about putting it out of commission.

Just a quick note regarding Moore's saying a MiG had overflown Site 85. I won't argue with him but I do want to say that I have read several accounts from USAF F-105 pilots who said a lot of people thought MiGs were overflying that area, when in fact they were F-105s setting their Doppler over Site 85's TACAN Channel 97.

Webb noted, "Suddenly everyone back at the embassy in Vientiane realized the vulnerability of the radar site at Phou Pha Thi" and as a result stationed a USAF combat air controller there. I think that is a bit misleading. Significant others at the embassy knew far in advance of this attack that LS-85 was very vulnerable, as you will see later in some detail. The problem I believe, was at 7th AF. Its leadership either did not believe Site 85 was vulnerable or, frankly, didn't care. Bombing NVN was more important as was the Trail.

Webb said the lead An-2 pilot had contacted a Dac Cong sapper team hidden at the base of the mountain. That team according to Webb "used its radio to visually guide the aircraft to drop mortars on the mountain." If correct, that means the sappers were there on January 12, 1968, perhaps for this very reason.

Webb said fresh battalions of NVA and Pathet Lao troops left Sam Neua City shortly after the An-2 attack, marching toward Phathi. He added intelligence sources on January 19, 1968 reported five battalions of NVA and Pathet Lao troops marching toward Phathi. He went on to say these deployments confirmed among many that LS-85 was now a high-priority target.

In response to the An-2 attack, Secord and Cline arranged for the Thais to send in 300 more troops, augmenting their force level to 400.

NVA Assault Team Plan

Correll said NVA mortars struck the southern end of the mountain with a 30-minute mortar attack on January 30, 1968. He said it was written off as a “probing attack.” I don't know who "wrote it off." Correll went on to report that the enemy was on all sides of the mountain, about seven miles away, by mid-February. Major Do commented that by mid-February 1968 the road had been extended to within 2,000 yards of the mountain. He said that was close enough for artillery. I'll talk about this road more later, but I know Major Secord called it Route 602. It had been on his radar screen a long time, since November 1967.

I have addressed the initial planning conference that set up the broad framework for the attack. So let's move to Major Do's explanation of his sapper team's assault plan drawn from the source reference I described earlier.

Major Do said the NVA sent out an eight man cell to reconnoiter the area on December 18, 1967, and confirmed the CIA command center was still there. Remember, the command center was located down the mountain a bit.

Major Do described what the NVA in the area had noted from its intelligence gathering. When Major Do employs the words "enemy" and "they," he is referring to those defending the site, friendlies to us, mostly Hmong:

  • The enemy placed a mixture of mines including electrically detonated B90 rounds and fences of barbed wire, concertina-wire, and tubes of explosives on the west and east sides.


  • There was a path up the east side. It had fresh water springs flowing year-round. There was also a wooden ladder on the east side. However the path crossed five hills held by the enemy. This is the area from which the NVA would attack.
  • Civilian defense forces (Hmong) went out on patrols around the footpaths that could be used. They tried to act like they were fishing or hunting or trying to till the fields, but they often fired many rounds including artillery illumination rounds trying to detect their enemy.
  • They would send out reconnaissance teams and frequently threw grenades down the hills.
  • They had a network of informants in the hamlets and villages surrounding their top positions.
  • Movement between the base and the mountain top was almost entirely by helicopter. There was some foot movement on the east side using the wood ladder.
  • They built fighting positions and obstacles and employed booby trapped mines.
  • The estimate was there were about 15 special enemy companies of fighting forces occupying the area.

Given what Major Do has said, the NVA planned to employ sappers to climb the mountain from its most steep point to attack the site. The four NVA infantry battalions would work against the Hmong at the base of the mountain and, as events permitted, perhaps go up the mountain, at least partly. My reading is no one on the friendly side thought about a scenario where sappers would climb the steep cliffs to conduct the main attack. However, recall early on during the TACAN installation Lt. Colonel Farnsworth opined the cliffs were "climbable." That was August 1966.

Furthermore, in the section on
US assessments and actions which comes after this section, I will tell you Farnsworth met with Lt. Colonel Blanton, the technician honcho, in Bangkok in late November or early December 1967. They met after Farnsworth's team had installed the TSQ-81. At that time Farnsworth told him he believed an attack was going to come and that it would be done by sappers.

Major Do said the attacking force would be one sapper team of 33 men from five different ethnic groups. There was a nine-man sapper squad for reinforcement, equipped with seven AK-47s, one B40 (rocket propelled grenade), one carbine, 57 hand grenades and satchel charges. It also was reinforced by a communications and cryptography squad to listen to enemy (friendly to us) communications. The sapper team attacking force’s primary target was the TACAN. There also would be a sapper team and infantry to conduct surprise attacks to prepare the battlefield.

Do added the attacking force had no infrastructure in the area. Most of the people opposed their revolution.


The attacking force positioned itself in vicinity of Muong-cau, in Muong-son District, about 40 kilometers (24 miles) northwest of Phathi. I believe Muang Cao (circled in yellow) on the map is Muong-cau in Major Do's description.

The enemy attack team had a very specific plan on who was going to do what to whom during the attack:

Assault Element 1

  • Cell 1 of three sappers would be the first to open fire. Its mission was to destroy and seize the American communications center, defend in place and wait for infantry to arrive.
  • Cell 2 of three sappers would coordinate with Cell 1 to destroy the enemy troops at the communications center, then move to the east of the helicopter pad and join with Cell 4 to attack the pad.
  • Cell 3 of five sappers would move toward the communications center and TACAN, seize them and kill all Americans in sight. Hold and wait for infantry to arrive.
  • Cell 4 would destroy enemy forces at the west end of the helicopter pad and then move east and engage any enemy attempt to counterattack toward the communications center and TACAN site.
  • Cell 5 of three sappers would be held in reserve, and support whomever needed it.
  • Assault Element 2
  • Cell 1 of three sappers would attack and seize the meteorological station and the 12.7 mm gun emplacement
  • Cell 2 of three sappers would destroy the defenders southwest of the meteorological station
  • Cell 3 of two sappers would destroy the Thai officers and technicians in two tents.
  • Cell 4 of four sappers would destroy the enemy platoon guarding the southeast side of the meteorological station.

I think this all leaves us with a good sense for the NVA plan.

Linkages: Vietnam and Laos
US tackles the linkages
Challenges to Rolling Thunder pilots
TACAN at LS-85
TSQ-81 at LS-85: Process to make it happen
TSQ-81 at LS-85: Installation
TSQ-81 operations
Situation Assessment: Houaphanh Province
NVA plans attack
NVA moves to attack positions
US threat assessments - actions taken
The NVA attack
The aftermath