The 1979 attack confirmed Hanoi's perception of China as a threat. The PAVN high command henceforth had to assume, for planning purposes, that the Chinese might come again and might not halt in the foothills but might drive on to Hanoi. The border war strengthened Soviet-Vietnamese relations. The Soviet military role in Vietnam increased during the 1980s as the Soviets provided arms to Vietnam; moreover, Soviet ships enjoyed access to the harbors at Danang and Cam Ranh Bay, and Soviet reconnaissance aircraft operated out of Vietnamese airfields. The Vietnamese responded to the Chinese campaign by turning the districts along the China border into "iron fortresses" manned by well-equipped and well-trained paramilitary troops. In all, an estimated 600,000 troops were assigned to counter Chinese operations and to stand ready for another Chinese invasion. The precise dimensions of the frontier operations were difficult to determine, but its monetary cost to Vietnam was considerable.