Surprised by the Marine landing at Wonsan, Chinese Communist Party chairman Mao Zedong called for the immediate destruction of the ROK Capital Division, ROK 3rd Infantry Division, US 1st Marine Division, and US 7th Infantry Division in a telegraph to Commander Song Shilun of the PVA 9th Army on 31 October. Under Mao's urgent orders, the 9th Army was rushed into North Korea on 10 November. Undetected by UN intelligence, the 9th Army quietly entered the Chosin Reservoir area on 17 November, with the 20th Corps of the 9th Army relieving the 42nd Corps near Yudami-ni.