The division returned to 21st Army in South China on 16 October 1939. The 21st Army was reformed to 22nd Army on 9 February 1940. As part of the newly formed army, the 5th Division became the core of the forces allotted for the Japanese invasion of French Indochina on 22 September 1940.
The division's return to its original assignment with the 21st Army in South China marked a significant shift on October 16, 1939. The 21st Army was subsequently reconstituted as the 22nd Army on February 9, 1940. As part of this new formation, the 5th Division became the primary force allocated for the Japanese invasion of French Indochina on September 22, 1940.