Yanmen Pass
Japanese forces, mainly the 5th Division and 11th Independent Mixed Brigade, moved out from Beiping and advanced on Huailai County in Chahar. A Japanese column advanced quickly into Shanxi, making use of the railway which the Chinese did not attempt to destroy. The Chinese abandoned Datong on September 13, falling back to a line from Yanmen Pass on the Great Wall east to the mountain pass of Pingxingguan. Yan Xishan's troops became more demoralised as the Japanese exerted their air supremacy.