5th Infantry Division's retreat route as well. The maneuver soon left the ROK 36th Regiment, 5th Infantry Division surrounded by PVA and they had to escape by infiltrating the PVA lines using mountain trails. By January 1, ROK III Corps was in full retreat, while the Corps' headquarters had lost contact with the 2nd and 5th Infantry Divisions. Responding to the crisis on the central front, ROK III Corps sector's defense was handed over to US X Corps. While the PVA were making a concentrated attack against the ROK front, the KPA forces that had infiltrated the UN rear were cutting the ROK withdrawal route. In the days before the Chinese Third Phase Campaign, KPA II Corps established a major roadblock to the north of Hoengsong with an estimated strength of 10,000 soldiers, which blocked the retreat of ROK III Corps. In response, ROK II Corps and the US 2nd Infantry Division conducted a siege operation against the roadblock from both the north and the south, and the roadblock was forced open by January 2. Although the UN forces managed to eliminate a KPA division at the roadblock, ROK II Corps was nearly destroyed during the fighting, and it was disbanded on January 10. The success of the initial PVA/KPA attacks forced ROK I Corps to abandon its attempts to restore its original defensive position at Hyon-ri, and a large number of KPA soon streamed into the gap between the US 2nd Infantry Division at Wonju and ROK I Corps on the east coast. Ridgway interpreted the attack on the central front as an attempt to surround the UN defenders at Seoul, and he immediately ordered their evacuation on January 3. On January 5, Ridgway ordered all UN forces to withdraw to the 37th parallel to set up a new defensive line, dubbed Line D, with the UN forces on central and eastern fronts setting up defenses between Wonju and the coastal city of Jumunjin (Chumunjin). At the same time, the PVA troops halted their offensive operations with KPA II and V Corps relieving the PVA 42nd and 66th Corps. Wonju falls In the aftermath of the ROK collapse, KPA V Corps proceeded to launch frontal attacks against US X Corps while KPA II Corps infiltrated the UN rear through the area to the east of Wonju. The US 2nd Infantry Division's position had now become an exposed northern salient,