Nankou Campaign, a.k.a. Operation Chahar, known by the Japanese as チャハル作戦 (Operation Chahar) and by the Chinese as the 南口戰役 (Nankou Campaign), occurred in August 1937, following the Battle of Beiping-Tianjin at the beginning of the China's War of Resistance against Japan and the Second World War.This was the second attack by the Kwantung Army and the Inner Mongolian Army of Prince Teh Wang on Inner Mongolia after the failure of the Suiyuan Campaign (1936).