Part Four: Mekong Convoy

In April, John Gunther Dean, the last US ambassador to Cambodia before it fell to the Khmer communists, turned over thousands of documents to the Jimmy Carter Library in Atlanta, Ga., part of the US National Archives. In part, the documents show the US mission’s efforts in Phnom Penh to bring Cambodia’s civil war to a peaceful close. The documents also detail some of the war’s fiercest fighting, along the Mekong River. The outcome of the first few weeks of 1975 would determine the future the Khmer Republic. This is the fourth in a series of reports on the Dean documents. 

Two Khmer Republican soldiers carry a wounded comrade past a machine gunner's post north of Phnom Penh, in 1975. The Khmer communists kept Republican troops busy around the capital while the communists fought for total control of the Mekong River in the south. (AP Photo)

When the 1975 dry season began, the communists launched their annual offensive. They overran garrisons along the Mekong River while pressuring bedraggled Republican troops around Phnom Penh, keeping potential reserve forces caught up in the capital. Already, supply runs up the river were dangerous, with communists firing on supply barges with large-caliber rifles, mortars and rockets. The dry-season offensive was wounding or killing 1,000 combatants per day. 

By mid-January, the river had become a crux issue, and Dean hoped for a symbolic supply run up the river. In a priority telegram to the State Department on Jan. 18, Dean informed Washington: “The next 48-72 hours will be crucial for Cambodia.” 

“If the enemy succeeds in closing the Mekong from the Vietnamese border up to Phnom Penh, he will have achieved his primary objective in this dry season: to strangle the [Republic] by preventing essential commodities from reaching the capital,” he wrote. 

No river supply line meant no efficient way to supply the capital, making additional funding from Congress even less likely for the beleaguered Republic. Meanwhile, an estimated 41 communist battalions, overrunning Republican garrisons, were dug in along the Mekong banks in well-fortified positions. Dean began calling the stretch of river between Vietnam and Phnom Penh “the gauntlet.”  

By Jan. 19, US and Cambodian planners had decided to run a supply convoy up the river. 

“It is imperative that this convoy reach Phnom Penh. The Khmers all know it—both friendly and enemy—as well as this mission,” Dean wrote. 

Their attempts were first thwarted by poor weather, which delayed the operation 24 hours, and again by a communist barricade across the river.  Two of four landings on the Lower Mekong were reclaimed by Republican forces, through amphibious assault, and the convoy was set for the next day. Again, the operation stumbled. On Jan. 21 the ambassador informed Washington a new bomb would be used in the conflict, the CBU-55. 

“CBU-55 is an anti-personnel bomb of considerably more lethal nature than anything previously used” by the Khmer Air Force, Dean wrote. “It contains propane, not as an agent of chemical warfare, but as a highly explosive charge which triggers off continuing series of explosions over period of time. Idea is to use it against deeply entrenched bunker positions enemy has constructed along Mekong banks.” 

With renewed, more powerful bombing planned and more fighting ahead, the military renewed its plans for the convoy, which was shrunk from 10 barges to just two, “pulled by the most powerful tugs available and fully protected by armored shields.”  

“If they make it, it would have a favorable psychological impact upon Khmer military by signaling that the enemy had not closed the river to traffic and that friendly forces could contain the [communists], and also upon river pilots and crews waiting to take the ships up the Mekong to Phnom Penh, whose morale and willingness to sail has been undermined by scare stories about [communist] might on the Mekong,” Dean wrote. 

On Jan. 22, Dean cabled Washington with bad news. 

“The two ammo barges are presently stopped between the Vietnamese border and Neak Loeung, where one of the tugs is awaiting engine repair,” he wrote. “The convoys successfully navigated through the narrows north of the Vietnamese border (except for losing two shield barges), but apparently crews and captains of tugs refuse to take convoy northward to Phnom Penh and wish to return to Saigon. Even if this small convoy can be pushed through, we clearly are now facing a new serious problem, that of the civilian crews refusing to take the ships up to Phnom Penh.” 

At last, a few convoys made it. But in the end, the communists held, and hope faltered. Dean sent Washington a bleak assessment: the national army was holding on by the “skin of its teeth,” and, despite propane bombs, amphibious assaults, reinforcements and powerful tugs toting armored barges, the Mekong was closed. Even if the Republican army broke the blockade, the communists were likely to exact a heavy toll on any supply runs from Vietnam. 

A controlled solution looked farther away than ever, and in the months that followed, in the face of diminishing prospects, the ambassador’s calls for negotiation would turn urgent.