In their determination to keep important transportation routes open despite US and South Vietnamese bombings, the North Vietnamese have developed a unique bridging technique that greatly reduces the vulnerability of bridges to aerial interdiction. The technique is based on the use of parallel steel cables drawn taut and secured on anchorages at each end. Prefabricated wood sections are secured to the cables to provide the bridge deck. Except on cable bridges constructed for rail lines, the decking is removed during daylight hours. With the deck removed the bridge is far less vulnerable to bomb damage than conventional bridges. Twenty-four cable bridges, in various stages of construction --including one in Laos-- have been detected since the beginning of June. These bridges are located, for the most part, along the highways comprising the major logistic network for the resupply of Communist forces in Laos and South Vietnam. Ten of the bridges, including four rail bridges, are located in Military Region IV, the principal staging area for the infiltration of men and supplies into South Vietnam. With one exception the gross load capacity of these bridges ranges between 10 and 20 short tons. This capacity is adequate to accommodate all but the very largest trucks in the North Vietnamese inventory. The rapid increase in sightings of cable bridges and the sharp increases in imports of large-diameter steel wire rope -- principally from Japan -- indicate that the North Vietnamese will make even more use of this innovation. The cable bridges permit more continuous use of railroads and highways and will reduce substantially the effort required to repair bomb damage.