'Fu' (i) was the Japanese seizure of Vichy French Indo-China (22/26 September 1940).

By February 1939, when Japan took the substantial Hainan island off the south coast of China, the Japanese threat to French Indo-China had become significant, for the latter was a conduit for the delivery of Allied weapons to China, was a major food producer and exporter, and also offered the physical opportunity for the extension of Japanese influence and military power farther to the south into Thailand and, possibly, the British colony of Malaya.

Appeals to the French government resulted in the arrival of limited reinforcements for French Indo-China, but the availability of additional financial resources made it possible for Général d’Armée Georges Albert Julien Catroux, who had been appointed governor-general in August 1939, to raise the strength of his forces to 100,000 men including 20,000 soldiers of the French Foreign Legion.

A a date early in 1940, Japanese troops moved to seize Longzhou in the south of the Chinese province of Guangxi, where the eastern branch of the railway from Hanoi in northern Indo-China reaches the border, and also tried to move west to cut the railway line to Kunming. The Chinese resistance, aided by supplies delivered via Indo-China, was considerable.

Then, taking advantage of France’s defeat by Germany in 'Sichelschnitt' and the following 'Rot' (iii), and the establishment of the Vichy French rėgime in that part of France left unoccupied by the Germans, and from which the new French regime controlled most of France’s overseas empire including Indo-China, during June 1940 the Japanese demanded the presence of a military mission in the country to ensure the closure of the railway line linking Yunnan in China with the port of Haiphong in Vietnam, the principal route by which Generalissimo Chiang Kai-shek’s Nationalist Chinese forces fighting the Japanese in the 2^nd Sino-Japanese War (1937/45) were supplied with external assistance.

Japanese forces at this time captured Longzhou, closing one railway supply route into China, but the other railway line to Yunnan was still open, and Japanese bombing was unable to close it.

Despite the availability of increased forces, Catroux felt he was in no position to oppose the Japanese demands, but the new Vichy French government disagreed and replaced him with Vice-amiral Jean Decoux, and when the Japanese made further demands Decoux was ordered to negotiate rather than fight. In fact, the Japanese had no desire to replace the French administration so long as they had full access to French Indo-China’s resources, which they then acquired through a blend of threat and astute diplomacy.

Japan joined Germany and Italy in the Tripartite Pact (also called the Three-Power Pact, Axis Pact, Three-way Pact and Tripartite Treaty) on 27 September 1940: this military alliance created the Axis powers of World War II in opposition to the Allied powers.

By this time Germany had already defeated France, resulting in the establishment of a semi-puppet regime in the region of France not occupied by the Germans. This regime had its capital at Vichy in that part of France left unoccupied by the Germans, and maintained a hold on large parts of the French empire, including French Indo-China (the protectorates of Annam, Cambodia, Laos and Tonkin, and the colony of Cochin-China).

Before this, on 5 September Lieutenant General Richi Ando’s South China Area Army had organised the amphibious Indo-China Expeditionary Army to move into Indo-China. Commanded by Major General Takuma Nishimura, this comprised Major General Takeshi Sakurada’s Indo-China Expeditionary Infantry Group, Colonel Kunio Osonoe’s 2^nd Imperial Guards Regiment, the Indo-China Expeditionary Tank Unit (14^th Tank Regiment), the Indo-China Expeditionary Aanti-Aircraft Artillery Unit, and the standard support elements. The Indo-China Expeditionary Army was supported by a flotilla of ships as well as naval warplanes operating from the fleet carrier Hiryu and seaplane tender Kamikawa Maru and army aircraft of the 1^st Hikodan and 3^rd Hikodan operating from air bases on Hainan island.

Faced with this invasion threat, Vichy France yielded. On 22 September, Japan and Vichy French Indo-China signed an agreement whereby Japan gained the rights to station troops in Indo-China and also to move troops, equipment and supplies through Indo-China. The accord allowed as many as 6,000 Japanese troops to be stationed in Indo-China, with no more than 25,000 troops to be stationed in or in transit though the country any given time. In addition, all Japanese land, sea and air forces were barred from Indo-Chinese territory and waters except as specifically authorised by the agreement, and any exceptions to these agreements would require Vichy French approval.

On 22 September 1940, the very day on which Decoux signed one of the agreements, the Japanese feigned ignorance of it and, within hours of the accords' signature, Lieutenant General Akihito Nakamura’s 5^th Division of Lieutenant General Kuichi Tanaka’s 23^rd Army in Canton crossed the border from China into Indo-China at three points near the rail junction at Lang Son, some 10 miles (16 km) inside northern Vietnam. This movement contravened the new accords, and the Vichy French authorities in Hanoi faced an immediate crisis. The Japanese division comprised the 11^th, 21^st and 42^nd Regiments, together with the 5^th Field Artillery Regiment, as well as small numbers of light and medium tanks. In all, Nakamura’s strength was about 30,000 men.

On the Vichy French side, the forces of the Lang Son sector, under the command of Général de Division Germain Stanislas Victor Mennerat’s 2ème Brigade, included five battalions of infantry, a group of tanks, a group of 75-mm (2.95-in) guns and a battery of 155-mm (6.1-in) howitzers, totalling about 5,000 men and centred on the 3ème Régiment Tirailleurs Tonkinois, 9ème Régiment d’Infanterie Coloniale and 5ème Régiment Etranger.

The Japanese attack began at 22.00 on 22 September. Its northern column took Bi Nhi on the border and advanced up the road to the north toward That Khe, which was defended by one company, away from the main battle. The main effort came from the central column, which crossed the border at Nam Quam, pushed aside two companies of the 2/3^rd RTT, and then turned south at Dong Dang along the road and railway. The southern column rolled through the platoon holding Chima and attacked Loc Binh; there the bulk of a company of the 2/3^rd RTT withdrew south with the intention of covering Na Dzuong, where it was reinforced by elements of 9^th RIC while the Japanese pushed north to support the central column’s drive on Lang Son and cut the rail link with Hanoi.

Thus Lang Son was threatened by the southern column and by the central column moving down from the north. As the Japanese columns advanced on 23 September, the Vichy French commanders sought to reimpose control on the confused situation. Reserves were dispatched to the sector, but by the afternoon the Japanese spearheads were already approaching Lang Son from the north, and the airstrip there was rendered inoperable by bombing during the afternoon. On the next day, the 4/3^rd RTT, which had been brought up from its frontier posts in the night, attempted a counterattack in the direction of Dong Dang, but was forestalled by a Japanese thrust by part of the central column from that town toward Khanh Khe. Most of the Vietnamese troops of the Vichy French battalion melted away, leaving only the French elements.

Meanwhile, the central and southern Japanese columns continued to tighten their hold on Lang Son. The local Vichy French commander considered a retreat while there was still a route available for such a move, but was ordered from Hanoi by Général de Corps d’Armée Maurice Paul Auguste Martin, the commander-in-chief, to hold the town.

To the south of the Song Ky Kong, the Japanese column took advantage of confusion among the defenders to push to the edge of town. Tp the north of the river in Ky Lua, the Japanese opened their 25 September assault against the 1/3^rd RTT with heavy artillery preparation at 05.30. Three hours later Mennerat notified Hanoi that Lang Son, isolated and untenable without air and artillery support, must surrender. At 10.40 Martin granted permission and, following local negotiations, the bulk of the 1/3^rd RTT and 2/5^th REI, the remnants of the 1/9^th RIC, and the brigade headquarters fell into Japanese hands.

The capture of Lang Son on 25 September released the bulk of the 5^th Division for other operations, and also opened the way south to Hanoi. Still in position, though, were the Vichy French defenders at That Khe in the north, Na Dzuong in the south and, in the critical sector, fresh battalions barring the route from Lang Son at Lang Giai and Lang Nac. During this activity in the border region, Japanese warships and transports of Vice Admiral Mineichi Koga’s 2^nd Fleet lay off the coast in the Gulf of Tonkin but the garrison troops which they carried, under the terms of the accords, were denied permission to disembark. Nishihara, having just signed those accords, departed Haiphong aboard the destroyer Nenohi on the night of 23/24 September and joined the task force.

In the morning Japanese aircraft began flights for reconnaissance and intimidation. A Vichy French envoy boarded the light cruiser Sendai (flagship of the 3^rd Destroyer Squadron with its two destroyer divisions) to open negotiations, but in the meantime the shore defences remained under orders to open fire against any attempt to force a landing.

A tense stand-off ensued. At 03.30 on 26 September Japanese forces came ashore across the beaches at Dong Tac, to the south of Haiphong, and immediately set out for the port city. A second landing put tanks ashore and at 06.30 Haiphong was bombed, 37 civilians being killed. By 13.00, led by a dozen tanks, the Japanese force of some 4,500 troops reached Haiphong. These skirmishes came as a result of the aggressive attitude taken by the Japanese army, which appears to have been wholly unconcerned about such diplomatic niceties as accords.

On 23 September Vichy France had hurriedly approached the government in Tokyo to protest this breach of the agreements so recently concluded. Two days later the Emperor Hirohito ordered an end to hostilities, and by the evening of 26 September fighting had died down. Nishihara returned to Haiphong on 29 September was soon replaced as head of the Japanese mission by Lieutenant General Raishiro Sumida, who seems to have been more able to satisfy Vichy French feeling.

By the middle of October all POWs had been exchanged except 200 German legionnaires of the 5^th REI who remained in Japanese custody. Japan took possession of airfields at Gia Lam, Lao Kay, and Phu Lang Thuong and stationed 900 troops in the port of Haiphong and a further 600 in Hanoi. The Vichy French forces reoccupied Lang Son, and in the course of October and November the 30,000 men of the reinforced 5^th Division completed their move from China to Indo-China. The same division went on to participate in the conquest of Malaya and Singapore in 1941/42.

In June 1941, after their demands for bases in Indo-China had been met, the Japanese occupied Saigon and moved into Cambodia. The Japanese solidified their control over Indo-China in July 1941.

In the preceding month Germany had started its 'Barbarossa' invasion of the USSR, and Berlin, desiring Japan’s support in this enormous undertaking, hoped that its ally would attack the USSR’s Asian coast. To encourage the Japanese to declare war on the USSR, the Germans imposed pressure on the Vichy French government to sign an accord for the 'common defence' of French Indo-China.

The Japanese now had a free hand in Indo-China. They could station troops wherever they wanted. They could use army and naval bases for their own military purposes, and were now free to install their own police force. Vichy France signed separate economic agreements that guaranteed to Japan virtually all of Vietnam’s rice, rubber, and mineral exports. In payment the French received restricted Japanese yen, which could be spent only in Japan itself. The agreements did confirm France’s sovereignty in Indo-China, but the French had to share this sovereignty with the Japanese. Although Indo-China was not technically occupied by Japan, the two countries settled down to an uneasy joint control.

On the other side of the South China Sea, General Douglas MacArthur, the head of the Filipino armed forces, and President Manuel Quezon of the Philippines were alarmed as the occupation of Saigon and the arrival of ever-larger numbers of Japanese troops in Indo-China seemed to presage an invasion. The two men communicated with an already highly alarmed US government, and on 26 July President Franklin D. Roosevelt signed executive orders to freeze all Japanese and Chinese assets, forbid the export of oil, iron and rubber to Japan, and deny use of the Panama Canal to Japanese shipping. At the suggestion of Roosevelt, the British government and the Dutch government-in-exile applied similar embargoes on Japan. Japan saw this as an insult by the western world, and this reaction perhaps sealed the future for war.

To prepare for their planned 'E', 'B' (ii), and 'J' and 'L' invasions of Malaya, Borneo and the western part of the Dutch East Indies respectively, some 140,000 Japanese troops were moved into southern Indo-China from 28 July 1941.