Following his instructions, ROK III Corps was placed around Chuncheon while ROK I Corps was deployed on the east coast. Meanwhile, ROK II Corps, with its strength reduced to a single infantry division in the aftermath of the Ch'ongch'on River battle, filled the gap between ROK I and III Corps. However, with the absence of US X Corps, the UN defenses on the central and eastern fronts were stretched thin, and there were gaps between the understrength ROK units. Because the ROK forces had suffered nearly 45,000 casualties by the end of 1950, most of their units were composed of raw recruits with little training, and out of the four ROK divisions that defended Chuncheon, only one was deemed battle worthy. Taking advantage of the situation, the KPA forces had been probing the ROK lines since mid-December, while thousands of North Korean guerrillas harassed the UN rear area from their mountain hideouts. On December 27, 1950, KPA II Corps managed to move behind the UN defenses by mauling the ROK 9th Infantry Division on ROK I Corps' left flank at Hyon-ri. This development threatened to destabilize the entire UN eastern front. In order to defend against the KPA penetration, Ridgway ordered US X Corps to reinforce the ROK defenses. However, with most of US X Corps still assembling at Pusan, the only unit that was available in the Eighth Army's reserve was the US 2nd Infantry Division, which was still recovering from its earlier losses at the Ch'ongch'on River. On December 28, Ridgway ordered the US 2nd Infantry Division to defend Wonju while placing the division under US X Corps control. After the US 7th Infantry Division of US X Corps finished reorganization on December 30, Ridgway ordered Major General Edward Almond, commander of the US X Corps, to develop Route 29 as its main supply route, and the 7th Infantry Division was subsequently tasked with defending it. In coordination with the Chinese assaults against Seoul in the western sector of the Third Phase Campaign, the North Koreans deployed the KPA II, III and V Corps, an estimated 61,500 soldiers, against the UN forces on the central front. The KPA plan was a frontal attack at Wonju by Major General Pang Ho San's KPA V Corps, while Major General Ch'oe Hyon's KPA II Corps would infiltrate the US X Corps' rear as guerrillas and block Route 29. The aim of