 On July 17 , the KPA 's 5th Division entered Yongdok , taking the city without much resistance before fierce UN air attacks caused the division heavy losses . Still , it was able to surround the ROK 3rd Division in the city . By now , the 5th Division and the 766th Regiment had been reduced to a combined strength of 7 @,@ 500 men to the ROK 3rd Divisions ' 6 @,@ <unk> . The 766th massed its force again to assist the 5th Division in surrounding and besieging the ROK 3rd Division , which was trapped in the city . The 3rd Division , in the meantime , was ordered to remain in the city to delay the North Koreans as long as possible . It was eventually evacuated by sea after delaying North Korean forces for a considerable time . The rugged terrain of the mountains prevented the North Korean forces from conducting the <unk> maneuvers they had used so effectively against other troops , and their advantages in numbers and equipment had been negated in the fight . 
