The Battle of Onjong was one of the first engagements between Chinese and South Korean forces during the Korean War. It took place around Onjong in present-day North Korea from 25 to 29 October 1950. As the main focus of the Chinese First Phase Offensive, the People's Volunteer Army (PVA) 40th Corps conducted a series of ambushes against the Republic of Korea Army (ROK) II Corps, effectively destroying the right flank of the United States Eighth Army while stopping the UN advance north toward the Yalu River.