Of all the North Korean attacks along the Pusan Perimeter , the Second Battle of Naktong Bulge is seen by historians as the most serious threat . It was the battle in which the North Koreans made the most substantial gains , splitting the US 2nd Infantry Division in half and briefly capturing Yongsan , where they were very close to breaching through to the US forces ' supply lines and threatening other divisions ' rear areas . However , once again the fatal weakness of the North Korean Army had cost it victory after an impressive initial success — its communications and supply were not capable of exploiting a breakthrough and of supporting a continuing attack in the face of massive air , armor , and artillery fire that could be concentrated against its troops at critical points . By September 8 , the North Korean attacks in the area had been repulsed .