Alarm Belt

It is a grim irony that Viet Nam's bloodiest battleground should be called the Demilitarized Zone. The DMZ, established in 1954 to keep peace between the two Viet Nams, is a running sore. Across its six-mile width come Northern Communist troops to strike and then scuttle back over a frontier that U.S. fighting men are forbidden to cross. Other battalions slither between Marine outposts to attack from the rear, undermining Saigon's rule in its northernmost provinces.

Secret Weapon. Marines are fighting ferociously guarding the DMZ in 1967, but the invasion continues unabated. And so, in an effort to stanch this wound, Defense Secretary Robert S. McNamara last week confirmed long-rumored plans for a 47-mile barrier across Viet Nam just below the DMZ. It will stretch from the South China Sea to Laos, running only 25 miles south of the two great walls of Dong Hoi and Truong Duc, erected in the 1630s by the Nguyen dynasty to fend off the warring Trinh emperors of the North.

Military engineers will start work late this year or early in 1968 on the barrier, known so far to the Pentagon as Project Dye Marker and immediately nicknamed "McNamara's Wall." But it will be no ordinary wall: instead of a Maginot line of concrete and steel, great tracts of rugged, mountainous jungle will be guarded by hidden electronic devices. Some, no larger than a silver dollar, can be seeded by aircraft; once in place, they will detect the movement of the smallest enemy groups and transmit warnings to gun crews miles away. "We are getting better and better at this sort of thing," says Charles M. Herzfeld, until recently director of the Defense Department's Advanced Research Projects Agency. "I think that it is really our secret weapon." Still, there are plenty of bugs in the system: rats, dogs, or even rainfall can trigger the gadgets--and it rains an average of 120 inches during the monsoon. Other zones will be swept by radar. Hair-thin trip wires, mine fields and conventional barbed-wire entanglements will block several notorious invasion routes.

McNamara's news was greeted sympathetically by Washington critics of the war, who see the barrier as a possible first step to scale down the bombing of North Viet Nam. Senate Majority Leader Mike Mansfield has urged such a barricade since April. But there was little enthusiasm from soldiers. They oppose any attempt to tie down troops in static positions while the enemy roams free. "Militarily, it's no great shakes," grumbled a Marine officer. An Army general was kinder. "I guess it can't hurt anything," he hazarded, "if it doesn't draw men or resources away from something important."

Childish Stories. At the risk of erecting a credibility wall between himself and the public by leaving almost every question unanswered, McNamara forbade all discussion of the barrier by military men to stop any seepage of information valuable to the enemy. Although he promised to keep Congress up to date, American taxpayers may never know the cost ($1 billion over two years, according to one estimate) or the effectiveness of McNamara's stratagem.

At best, the barrier can re-demilitarize the DMZ and discourage North Vietnamese regulars from frontal forays against Marine outposts. But it cannot block the end run down the Ho Chi Minh Trail already made by thousands of invaders, or prevent men and munitions from being landed along the coast by night. "We know, of course," McNamara conceded, "that no obstacle system can stop the infiltration of personnel or supplies." North Vietnamese Major General Tran Do, deputy commander of Communist forces in the South, doubtless concurred. When rumors of the barrier were bruited about last year, he ridiculed them as "childish stories." "What is the use of barbed-wire fences," scoffed Do, "when we can penetrate even Tan Son Nhut Air Base outside Saigon?"

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