The Indispensable Lifeline

THE current allied offensive got started after military analysts warned that the Communists were engaged in the greatest overland supply effort of the Viet Nam War. Men and material were being transported, they said, over the route that had long since become a kind of guerrillas' Appian Way in Southeast Asia: the Ho Chi Minh Trail. The U.S. has been interdicting the trail since 1964, and last week completed its 122nd consecutive day of intensive bombing. The holocaust has frequently slowed down the Communists but seems incapable of stopping them.

The trail is like a 4,000-mile spider web, a tangled maze of routes ranging from yard-wide footpaths to short sections of gravel-paved highway two lanes wide. The system threads westward out of three North Vietnamese passes (the Mu Gia, Ban Karai and Ban Raving), which cut through the Annamese mountains, then loops south and east for 200 miles, reaching a width of 50 miles at some points. Studded with lumpy hillocks, the trail network cuts through the precipitous terrain and dense, triple-canopied jungle growth. -

Traffic down the trail always increases after the monsoon season ends in September or October. It reaches a peak from February to April, the last months when supplies can leave the north and still reach their destination before rains again make the roads impassable in May. This year the trail's cargo has become more vital than ever to the Communists. Since last March, they have been denied the use of the Cambodian port of Kompong Som, where some 75% of the war material for all of South Viet Nam used to be shipped by sea. Thus, except for what they can forage, the some 400,000 Communist troops in southern Laos, Cambodia and South Viet Nam are almost totally dependent on the trail for their supplies and reinforcements.

Troop infiltration, which has run as high as 17,000 a month in the current dry season, is hardest to detect. Recruits are marched single file along foot trails at intervals of five yards, each wearing camouflage greenery. The trip takes between three and five months with occasional stops in primitive way stations for rest and resupply. The attrition rate due to disease, bombing and desertion runs as high as 15%; yet Hanoi keeps sending replacements.

Truck traffic is equally relentless. Each night a fleet of some 1,000 convoy trucks rolls out from hiding places in limestone caves and bunkers and moves south. Each driver covers the same 15-to 40-mile stretch of road again and again until he can negotiate it blindfolded. There is a reason for that: headlights must be dimmed or even doused for much of the trip because of marauding aircraft. At the end of his run, a driver unloads his cargo at a transfer point and heads back for more. Each section, called a binh tram (logistical support) system, is under a separate command. "The man who runs a binh tram system is Mr. Greyhound," says a U.S. Air Force officer. "He says 'Send them down' or 'Hold them.' " Shipping time for any one load: about two months. -

To cut off that antlike flow, the U.S. has committed more than half of its air-power in Indochina to missions over the trail--about 380 sorties on an average day during the dry season. The raids are conducted by fighter-bombers, C-119 and C-130 gunships and giant B-52 Stratofortresses. Often they must dodge fire from some 3,000 artillery emplacements scattered along the trail. In addition to pilot reconnaissance, the Air Force is relying increasingly on an arsenal of electronic gadgetry developed to see and hear through darkness and vegetation. Two gadgets that have recently come to public attention in congressional testimony:

> Igloo White is an Air Force ground sensor system modeled on the Navy's acoustic submarine detectors. The sensors are dropped during overflights and either catch in tree branches or bury themselves in the ground. Two main types have been used: seismic, which detect ground movements caused by moving trucks and even marching soldiers, and acoustic, which use tiny microphones so sensitive that they can clearly transmit human voices (several conversations have been picked up among Communist troops discussing how to dismantle the sensor). Information from the sensors is relayed by planes to ground-based monitors stationed in South Viet Nam, who radio the coordinates to an aircraft for bombing.

> Pave Way is a targeting system using the laser beam. Once an object has been identified, an aircraft equipped with Pave Way can "fix" it with a brilliant laser light, then release bombs that are fitted with special light-seeking devices. The bombs are automatically guided to the laser-illuminated target.

The net effect of this massive effort, by the U.S. military's own estimate, is to keep about half of the Communists' supplies ' from reaching the South. As a result of the air campaign, U.S. commanders believe, the Communists must tightly ration their ammunition, which helps keep the level of fighting down. Of course, the Communists have the advantage most of the time of being free to set their own schedule for attack. "We make him pay a price for every ton," says an Air Force spokesman about the enemy. "But he never runs out of roads. It just drives you nuts."

The only way to eliminate traffic completely on the trail, military authorities argue, is to cut it on the ground. That, of course, may well be the ultimate goal of Operation Dewey Canyon II. The very fact that a ground operation, with all the risks it involves, is deemed desirable by military experts is a tribute to the Communists' herculean effort to keep the trail open as well as an admission that even the most modern airpower has its limits.

This file is automatically generated by a robot program, so reader's discretion is required.