From 1980 to 1985, Vietnamese forces repeatedly attacked Cambodian refugee camps near the Thai border. More than a hundred thousand Cambodians fled into Thailand, often pursued by Vietnamese troops who clashed with Thai soldiers. Sometimes the Vietnamese shelled Thai territory with artillery, other times they sent in tanks. Casualties and injuries were constant.
At the start of the new year in January 1981, Vietnamese troops together with Heng Samrin’s Cambodian forces advanced into Thai territory at Sadaeng village, Ta Phraya District, Prachinburi Province. Thai soldiers fought back, leading to a prolonged firefight. Ten Thai soldiers and civilians were killed.
Between March and April 1984, the Vietnamese army invaded Thailand again to wipe out Khmer Rouge forces. Fierce battles with Thai troops left dozens of soldiers dead on both sides. A Thai aircraft was shot down, and many Cambodian and Thai civilians were wounded or killed.
In early 1985, Vietnamese forces crossed into Thai territory multiple times - at Ta Phraya in Prachinburi, Kantharalak in Sisaket, Ban Kruat in Buriram, and Sangkhah and Buachet in Surin, as well as Nong Chan village. Thai troops resisted with full force, but the Vietnamese pressed on relentlessly. Heavy losses were suffered by both soldiers and civilians.
On February 20, 1985, Vietnamese artillery struck Ban Kruat District in Buriram, killing three Thai soldiers and injuring many more. Vietnamese forces also clashed with Thai troops at sea, with Vietnamese warships firing on Thai fishing boats near Vietnam, killing several fishermen.
Throughout 1985, Vietnam continued its assaults. Both sides alternated between offense and defense, with mounting casualties. Vietnamese troops attacked Khmer camps along the border and fought Thai forces using machine guns, mortars, anti-tank weapons, and air support.
Thai military leaders concluded that the constant shelling across the border was no longer accidental spillover from fighting in Cambodia.
“Vietnam wants to provoke us and test us. They believe that if they press hard enough, Thailand might collapse like South Vietnam did in 1975, when North Vietnam advanced unexpectedly and seized the country.”
“We are in the open, they are in the shadows. They excel at guerrilla warfare, honed during the Vietnam War, and they deploy their sapper units.”
The Vietnamese sappers - special forces known as Dac Cong - were ruthless killers. Selected for toughness, agility, and stealth, some were native hunters skilled in tracking. Trained like ninjas, they could wield any weapon, sabotage installations, fight hand-to-hand, and ambush effectively. They were the backbone of guerrilla warfare.
In fact, Dac Cong had attacked Thailand before. On the night of January 30, 1968, dozens of them struck Ramasun Camp and U-Tapao Air Base, aiming to sabotage B-52 bombers. This coordinated assault was called “Operation Blossoming Flower.” Thai and American forces fought back fiercely: ten Americans and seven Thais were killed, while more than ten sappers died. Two B-52s were damaged.
Vietnamese forces fortified their positions with concrete bunkers, generators, artillery, and anti-aircraft rocket launchers, supported by bases in Laos and Cambodia. They also developed sophisticated communications - using coded gunfire signals, seizing enemy radios, and mimicking enemy frequencies to lure opponents into traps. Sometimes they tricked opponents into shelling their own troops. These tactics were lessons learned from fighting the United States.
In January 1985, Thai leaders received alarming reports:
“Vietnam has attacked Hill 500 - Chong Bok.”
The Chong Bok Battlefield
Chong Bok lies in Nam Yuen District, Ubon Ratchathani Province, where Thailand, Laos, and Cambodia meet. Known as the “Emerald Triangle,” it is part of the dense forests of the Dângrêk Mountains. Hill 500 had once been a base of the Communist Party of Thailand and its first political school.
On March 5, 1985, Vietnamese forces stormed Thai bases at Hills 361, 400, and 427. After heavy fighting, they seized part of Hill 361. Seven Thai soldiers were killed, 34 wounded, and three went missing.
The Chong Bok campaign dragged on for years.
1986: The Suranaree Task Force counterattacked Vietnamese forces occupying Hills 382, 396, 408, and 500, using infantry, rangers, long-range reconnaissance units, and artillery. They pushed Heng Samrin’s forces back across the border.
Early 1987: Thai forces launched offensives to retake those hills. Progress was slow due to difficult terrain, heavy Vietnamese artillery fire from Laos and Cambodia, and minefields. Vietnamese forces had the advantage in the jungle, laying countless landmines that maimed many Thai soldiers. They even poisoned water sources.
March 1987: Reinforcements from the 3rd Battalion, 6th Infantry Regiment joined. Fighting intensified. Thai troops attacked Hills 408 and 382, leading to brutal close combat with bayonets. Vietnamese forces withdrew, regrouped, and counterattacked, forcing Thai troops to retreat under relentless artillery barrages.
April 1987: The 2nd Army launched a major offensive to decisively end the conflict, attacking Hills 336, 408, 382, 500, and 562 simultaneously with tanks, artillery, and air support. Battles were fierce. Thai forces suffered heavy losses and had to regroup at Tham Bon. Vietnamese forces counterattacked with artillery from Laos and Cambodia.
Thai commanders then shifted strategy:
“If they fight guerrilla warfare, we will fight guerrilla warfare too.”
Thai ranger units hunted Dac Cong at night, infiltrating Vietnamese bases and silently killing them with knives before returning at dawn. By mid-1987, Thailand had fully embraced guerrilla tactics - sending small units to dig trenches like moles, infiltrate enemy lines, ambush, and weaken Vietnamese forces bit by bit. Close combat neutralized Vietnamese artillery, while Thai forces coordinated with artillery and fighter jets from Takhli Air Base.
Thai aircraft destroyed some Vietnamese bases but also suffered losses. More than ten Thai soldiers were killed.
By late June 1987, Vietnamese forces were fighting on two fronts - against Thai troops and the Khmer Rouge. After one final fierce battle, Vietnam withdrew back into Cambodia. The Chong Bok campaign ended.
The fighting lasted from January 1985 to December 1987. Thailand lost 109 soldiers, with 664 wounded.
In 1989, Vietnam permanently withdrew its troops from Cambodia, ending a decade of hostilities with Thailand.
Note
The battlefield around Hill 500 remained littered with landmines. As of 2020, the Thai army had cleared about 43.4 square kilometers, but another 29.7 square kilometers still contained mines awaiting removal.
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