The Great Naktong Offensive was one of the most brutal fights of the Korean War. The five-prong offensive led to heavy fighting around Haman, Kyongju, Naktong Bulge, Nam River, Yongsan, Tabu-Dong and Ka-san. The KPA attacks made appreciable gains and forced the UN troops along the Pusan Perimeter to form a thin line of defense, relying on mobile reserves for the strength to push back KPA attackers. From September 18 this fighting was intense and the battle was a very costly deadlock for the two overextended armies. The KPA were initially successful in breaking through UN lines in multiple places and made substantial gains in surrounding and pushing back UN units. On September 4–5 the situation was so dire for the UN troops that the Eighth Army and ROK moved their headquarters elements from Taegu to Pusan to prevent them from being overrun, though Walker remained in Taegu with a small forward detachment. They also prepared their logistics systems for a retreat to a smaller defensive perimeter called the "Davidson Line". By September 6, however, Walker decided another retreat would not be necessary.