2nd Infantry Division to withdraw from Wonju while pulling the central and eastern fronts back to the area between Wonju and Samch'ok, and this resulted in another retreat. Ridgway also sent the US 187th Regimental Combat Team, the US 5th Cavalry Regiment, the US 1st Marine Division and the Greek Battalion to contain KPA guerrillas east of Route 29 and north of Andong and Yeongdeok. About 30,000 American infantry were deployed to the central front by mid-January, and the KPA guerrillas were blocked in a narrow salient along the hills at the east of Route 29. To eliminate the KPA threat in the UN rear, Almond ordered all X Corps units on Route 29 to launch aggressive patrols to destroy the KPA supply bases and guerrilla bands. Specially trained irregular forces, such as X Corps' Special Action Group, also hunted KPA units by operating as guerrillas themselves. The constant UN pressure slowly depleted the ammunition and the manpower of KPA II Corps, while Major General Yu Jae-hung rallied ROK III Corps and sealed the gap between Wonju and the east coast by January 22. On January 20, a patrol carried out by the US 9th Infantry Regiment, 2nd Infantry Division managed to reoccupy Wonju without much resistance. Lacking reinforcements and supplies, KPA II Corps was scattered by the end of January, and only 8,600 soldiers from KPA II Corps managed to survive and retreat back to North Korea. The KPA 10th Division, vanguard of KPA II Corps, was also annihilated by US 1st Marine Division during the UN anti-guerrilla operations. Aftermath By the end of January, KPA II Corps was decimated during its guerrilla operations, and its estimated strength was reduced from 16,000 to 8,000. KPA V Corps' attempt to capture Wonju had also resulted in crippling casualties, and its estimated strength was reduced from 32,000 to 22,000 by the end of January. In contrast, UN losses were relatively moderate during the same period. The defeat of the KPA enabled the UN forces to consolidate their positions along the Korean central and eastern front, and the retreating US Eighth Army on the Korean western front could finally return to the offensive after its rear and eastern flank were secured. As soon as US X Corps regained full control of the central front at the end of January, Ridgway ordered the US Eighth Army to launch Operation Thunderbolt against PVA/KPA forces