The vital seaport had to be held if the UN forces were to retain a foothold in the peninsula, and the enemy was already threatening both Pohang-dong and Masan, each within 50 miles. Only by courtesy could the irregular chain of UN positions have been called a line. Gaps were the rule rather than exception, and an entire enemy corps might have driven through the mountainous area between Andong and Yongdok without meeting serious opposition. Nor was this the only spot where the dangerously stretched UN forces had to depend on the terrain for support. Yet the time had come to make a stand, and this final UN beachhead has gone down in history by the name of the Pusan Perimeter. From Taegu in the center to the eastern coast, five depleted ROK divisions were arrayed during the first week in August. East of the Naktong, from the Taegu-Waegwan area southward, the 1st Cavalry and the 24th Infantry Division held defensive positions. This left the southern sector to the 25th Division, reinforced by the Army 5th RCT and the 1st Provisional Marine Brigade. The principal enemy units pressing toward Masan and Pusan in the southern sector were identified as the NKPA 6th Infantry Division and the 83d Motorcycle Regiment. Composed entirely of Chinese civil war veterans in July 1949, the 6th Division had at that time been the 166th Division, 56th CCF Army, which later entered Korea as a completely equipped unit. Its three infantry regiments, the 13th, 14th, and 15th, were distinguished throughout the invasion for a high esprit de corps. After capturing Yongdungpo, an industrial suburb of Seoul, the 6th had pushed southward and won fresh honors by forcing the river Kum and taking Kunsan by storm.[154] [154] FECOM, ATIS, _North Korean 6th Infantry Division_ (InterRpt, Sup No. 100), 33–6. On the eve of the Kunsan operation, according to a captured enemy document, troops of the 6th were informed that they were facing a United States Army regiment. “Since this unit is planning to advance to the north, it is our mission to envelop and annihilate it.... We are fully prepared and confident of success in this operation.”[155] [155] _Ibid._ A numerical superiority as well as good combat discipline enabled the initial assault waves to cross the Kum in pneumatic floats and establish a bridgehead before noon on 16 July 1950. Half of the town of Kunsan was occupied before nightfall, and the United States and ROK defenders withdrew under cover of darkness. Next came the “end run,” with 6th Division units racing toward the capture of Namwon, Kwangju, Yosu, and Mokpu in the southwest corner of the peninsula. No opposition awaited except ineffectual delaying actions by ROK constabulary troops. After mopping up a few small pockets of resistance, the 6th Division pushed eastward to lead the North Korean drive toward Pusan.