THE Pentagon's "Bombing Encyclopedia" for North Viet Nam lists 18,000 potential targets, ranging from a tumbledown bamboo bridge over a little-used canal to Ho Chi Minh's Hanoi headquarters. Only 5,000 of them are considered militarily significant, and most can be attacked at the Pentagon's discretion. Between 350 and 400 politically sensitive targets have been referred to President Johnson for his personal approval to raid them. To date, he has given the go-ahead on all but approximately 50.
In the 21 years since regular raids on the North were begun, the air campaign has gradually spread from the southern panhandle section of North...