Nation: 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...