During the last week of August , US troops on these hills could see minor North Korean activity across the river , which they thought was North Koreans organizing the high ground on the west side of the Naktong against a possible American attack . There were occasional attacks on the 9th Infantry 's forward positions , but to the men in the front lines this appeared to be only a standard patrol action . On August 31 , the UN forces were alerted to a pending attack when much of the Korean civilian labor force fled the front lines . Intelligence officers reported an attack was coming .