One hundred and fifty metres is not far. It is the distance the lead vehicle of a South Vietnamese cavalry column covered on 16 January 1971 after enemy fire set it alight on a Cambodian mountain road. The commander kept it rolling and kept his machine gun firing, because a stopped vehicle would have corked the whole column inside the kill zone. Hit three times and burning, the carrier ran those hundred and fifty metres and then blew apart, killing its crew. Behind it, the rest of the squadron drove clear. That is the shape of Operation Cuu Long 44-02 in miniature: a short, violent effort to keep a road open, paid for in specific lives on a specific afternoon.
Cambodia's Route 4 runs roughly 230 kilometres from Phnom Penh southwest to Sihanoukville, and it was built in the 1950s for exactly one reason: to tie a landlocked capital to a deep-water port. Cut it and the capital starves slowly. In September 1970, Khmer Rouge forces together with units of the People's Army of Vietnam's 1st Division did precisely that, occupying the Pich Nil Pass where the highway climbs through the mountains. Several outposts of the Khmer National Armed Forces, the FANK, were overrun; others were abandoned without a shot. The Mekong supply route still functioned, but the Mekong could not carry what Route 4 carried, and what the Cambodian government needed most was military equipment. When the FANK asked for help, the South Vietnamese Joint General Staff handed the problem to the commander of IV Corps, General Ngô Quang Trưởng.
Trưởng split his force in two and sent them at the pass from opposite ends. Task Force North - the 2nd Marine Brigade and the 12th Armor Regiment - rolled up Route 1 to Phnom Penh, then southwest down Route 4 toward Kompong Speu. Task Force South, built around the 4th Armor Brigade and the 4th Ranger Group, left Hà Tiên on the Vietnamese coast and pushed west along Route 16, intending to swing north and northeast until the two halves met somewhere in the middle. Overhead, the Republic of Vietnam Air Force's 4th Air Division flew from Binh Thuy, supplemented by American reconnaissance aircraft, tactical strike aircraft and B-52s. US fire-support and medical evacuation helicopters staged from An Thoi Naval Base on Phú Quốc island, close enough to reach the southern column quickly. A Vietnamese army, reopening a Cambodian highway, under American bombers: by 1971 the war had stopped pretending the borders meant anything.
The ambushes came in the south. North of Hà Tiên the 16th Armored Cavalry ran into prepared positions and did the counterintuitive thing, charging straight into them rather than stalling under fire. Days later the 12th Armored Cavalry met a better-laid trap: destroy the first vehicle and the last, and everything between them is caught. Only the first vehicle refused to die on cue. When it finally exploded, the column was already moving, and the Ranger battalion following behind had halted and opened fire, catching the ambushers between cavalry and infantry. Two US aerial fire teams closed the escape routes. When the shooting stopped, two hundred of the ambushers lay dead and seventy-five weapons were collected, including two 75mm recoilless rifles and three heavy machine guns. The 12th lost five men killed, twenty wounded and three carriers destroyed. The reports count the captured weapons far more carefully than they count who any of the two hundred had been.
On 17 January, FANK troops with Vietnamese Marine Corps support fought their way to the outskirts of the Pich Nil Pass and took it, while the armour secured Route 4 as far north as Route 18. The Vietnamese stayed long enough to help the Cambodians build strongpoints along the reopened highway, then turned for home; the 4th Armor Brigade was back inside South Vietnam by 25 January. Twelve days. Two hundred and eleven PAVN and Khmer Rouge dead, sixteen South Vietnamese. By the arithmetic of the period it counted as a clean success, and the road did carry traffic again. What it could not do was hold. Four years later, in April 1975, the Khmer Rouge entered Phnom Penh, and the army that Cuu Long 44-02 had come to help ceased to exist. Today the pass is simply a place where a busy highway climbs through green mountains, and nothing on the roadside marks the men of either side who died within sight of it.
The Pich Nil corridor sits at roughly 11.195°N, 104.074°E, where Cambodia's National Highway 4 threads the mountains between the coastal plain and the Phnom Penh lowlands. From 6,000-8,000 feet the terrain reads clearly: dark forested ridges on either side, the pale ribbon of Route 4 switchbacking through the gap, and the reservoir country to the northeast. Phnom Penh International (VDPP) lies about 50 nautical miles northeast; Sihanouk International (VDSV) about 45 nautical miles southwest, on the coast the road was built to reach. Morning haze is common in the dry season and the ridges generate afternoon build-ups through the May-October monsoon, so plan the pass transit early.