This was the Japanese coup d’état to remove the Vichy French regime in Indo-China (9 March 1945).
At this time French Indo-China comprised the colony of Cochin-China and the protectorates of Annam, Cambodia and Tonkin, and the mixed region of Laos. The government of French Indo-China had adhered to the Vichy French regime after the fall of France in June 1940 and remained loyal to it. After the coup, the Japanese replaced French officials and military personnel in the colonial infrastructures, but otherwise left the colonial areas more or less intact, though they did urge declarations of independence from the traditional rulers of the different regions, creating a new Empire of Vietnam, Kingdom of Cambodia and Kingdom of Laos under Japanese patronage.
A small-scale guerrilla warfare campaign followed, and in this Free French forces and their native allies on the one hand and the nationalist Viet Minh and Indo-Chinese Communist Party on the other both fought the Japanese. In August, the regime of puppet states collapsed with the surrender of Japan, and British, Chinese and French forces arrived to fill the vacuum, though the Vietnamese revolution by the Viet Minh, began in August and continued.
In 1945, the Japanese feared that the Allies might launch an offensive into French Indo-China where, despite the fall of Vichy France in Europe, its colonial administration survived despite the fact that the governor, Amiral Jean Decoux, had recognised and contacted the new provisional government of the revived French republic.
On the eve of the Japanese coup, the French garrison of Indo-China numbered about 65,000 men, of whom 48,500 were tirailleurs (locally recruited native troops) under French officers. The rest were French regular troops of the colonial army and three battalions of the French Foreign Legion. Since the fall of France in June 1940, these forces had received neither replacements nor supplies from outside Indo-China. In August 1940 Decoux had signed an agreement under which Japanese forces were permitted to occupy bases across Indo-China, and in the first weeks of 1945 there were about 30,000 Japanese troops in Indo-China, but this strength was substantially increased by the arrival of reinforcements from Burma in the following months.
Early in March, the Japanese forces were redeployed around many of the main French garrison towns, and on 9 March the Japanese delivered an ultimatum for the French troops to disarm: those who refused were usually massacred. In Saigon, senior Japanese officers invited the French commanders to a banquet, and at this those who attended were arrested and almost all were killed.
In Saigon the two most senior Vichy French officials, Général de Brigade Emile-René Lemonnier and Resident Camille Auphalle, were executed by decapitation after refusing to sign surrender documents. The most determined French resistance was at Dong Dang where a company of the Tirailleurs Tonkinois and a battery of colonial artillery held out for three days before being overrun and massacred.
The French up-country garrisons fared better, however, and under the leadership of Général de Division Marcel Alessandri, a column of 5,700 French troops, including many Foreign Legionnaires, fought its way through to Nationalist China.
The French administration was effectively dismantled, and the Japanese pressed the Empire of Vietnam, the Kingdom of Laos and the Kingdom of Cambodia to declare their independence. Emperor Bảo Đại complied in Vietnam and collaborated with the Japanese, and while King Norodom Sihanouk in Cambodia also obeyed, the Japanese did not trust this francophile monarch. The Cambodian nationalist leader Son Ngoc Thanh, who had been exiled in Japan and was considered a more trustworthy ally than Sihanouk, returned to become minister of foreign affairs in May, and then prime minister in August. In Laos, however, King Sisavang Vong, who favoured French rule, refused to declare independence, and found himself at odds with his prime minister, Prince Phetsarath Rattanavongsa.
China, which had given shelter to escaped French troops, and the USA were both reluctant for a number of reasons, including antipathy to the very idea of colonial rule, to commit themselves to any major operation to restore French authority. Both countries ordered their forces to provide no assistance to the French, but Major General Claire L. Chennault, commander of the US 14th AAF, went against orders and aircraft of his 51st Fighter Group and 27th Troop Carrier Squadron flew support missions for the French forces retreating into China.
Commandos of the Force 136 British liaison organisation had been conducting minor operations in French Indo-China since a time late in 1944 and, after the Japanese coup, French and British reinforcements were parachuted into Indo-China to undertake guerrilla operations against the Japanese, and were supplemented by French troops who had escaped from the Japanese coup in March.
French resistance groups had more latitude for action in Laos as the Japanese had less control over this part of the territory. However, the commandos lacked precise orders from their governments and the practical means to mount any large-scale operations. The French and Lao guerrilla groups also lacked significant firepower, but nevertheless managed to gain control of several rural areas.
In northern Vietnam, Hô Chi Minh’s Viet Minh started their own guerrilla campaign against the Japanese and established bases in the countryside without meeting much resistance from the occupying forces, whose greatest strength was concentrated in the cities. The Viet Minh lacked the military strength to launch a full-scale attack against the Japanese, and their actions were limited to a few attacks against Japanese army posts.
In France, a Corps Expéditionnaire Français en Extrême-Orient (French Expeditionary Corps in the Far East) was established under the command of Général de Corps d’Armée Philippe François Marie Jacques Leclerc de Hauteclocque, and was being readied, albeit slowly, for despatch to Indo-China to fight the Japanese.
The Japanese surrendered before this could take place, however, when Emperor Hirohito announced Japan’s capitulation on 15 August 1945, and on the following day the Japanese garrisons officially handed control to Bảo Đại in the north and the United Party in the south. This, however, allowed nationalist groups to take over public buildings in most of the major cities. The Viet Minh were thus presented with a power vacuum, and on 19 August there took place the August Revolution in which the Viet Minh took power.
On 25 August, Bảo Đại was forced to abdicate in favour of Ho and the Viet Minh, and at this time the Viet Minh took control of Hanoi. In most of French Indo-China, the Japanese did not oppose the Viet Minh assumption of power as they were reluctant to let the French retake control of the colony, and the French troops who had been arrested in March were kept in jail by the Japanese. Japanese troops clashed briefly with Viet Minh guerrillas in Annam, but there were no major military engagements other than in Thái Nguyên Province, where Japanese troops refused to surrender and did battle with the Viet Minh from 20 to 25 August. The Japanese finally surrendered on 26 August, and the Viet Minh seized their weapons. Hô proclaimed Vietnam’s independence on 2 September 1945.
British troops, in the form of Major General D. D. Gracey’s Indian 20th Division, and Chinese nationalist troops entered the country and began to disarm the Japanese, and were complemented by elements of the Corps Expéditionnaire Français en Extrême-Orient when they started to arrive in September.
French Indo-China was left in chaos by the Japanese occupation. Decoux, who had supported the Vichy French regime instead of Free France, was sent to France to face trial. In Laos, Phetsarath Rattanavongsa’s Lao Issara deposed the king in October and declared the country’s independence, but its government had to flee in April 1946 as French troops advanced toward Vientiane, the capital. In Cambodia, Son Ngoc Thanh was arrested by the French. Ho Chi Minh found himself in partial control of north Vietnam, setting the stage for the 1st Indo-China War (1946-1954) in which the French were finally ousted from Inmdo-China.