Japanese Occupy Wuyuan
On 3 and 4 Feb, Wuyuan and Linhe were taken successively.
On 20 Mar, Chinese General Fu Zuoyi's 35th Corps, the New 31st Division, and a regiment of the Garrison Brigade, which had been secretly moving east along the Wuchia River, attacked Wuyuan by surprise. Initial Japanese resistance was fierce, with the front lines moving back and forth, causing casualties on both sides.
The Japanese call it 第２次後套作戦 , The second battle of Wuyuan. By the 28th of January 1940 the Japanese had built up forces from 26th Division at Baotou sufficient to launch the 第１次後套作戦 or "First battle of Wuyuan in Inner Mongolia" to recover lost territory and move west to take Wuyuan which fell on February 3rd and Linhe further west on the 4th of February.
Japan's Economic Expansion into Manchuria and China in World War Two