The Japanese Invasion of French Indochina; also known as the Vietnam Expedition; was a move by the Empire of Japan in September 1940; during the Second Sino-Japanese War; to prevent China from importing arms and fuel through French Indochina; via the Sino-Vietnamese Railway from the port of Haiphong through Hanoi to Kunming in Yunnan.

Japan occupied northern Indochina; which tightened the blockade of China; and made continuation of the drawn out Battle of South Guangxi unnecessary. In March 1945; Japan launched the Second French Indochina Campaign and ousted the Vichy French and formally installed Emperor B?o ?i in the short-lived Empire of Vietnam. In August 1945; Japanese forces surrendered in Indochina at the end of World War II.