1945 overthrow of the French Indochina government by the Japanese
The Japanese coup d'état in French Indochina, known as , was a Japanese operation that took place on 9 March 1945, towards the end of World War II. With Japanese forces losing the war and the threat of an Allied invasion of Indochina imminent, the Japanese were concerned about an uprising against them by French colonial forces.
Despite the French having anticipated an attack, the Japanese struck in a military campaign attacking garrisons all over the colony. The French were caught off guard and all of the garrisons were overrun, with some then having to escape to Nationalist China, where they were harshly interned. The Japanese replaced French officials, and effectively dismantled their control of Indochina. The Japanese were then able to install and create a new Empire of Vietnam, Kingdom of Kampuchea and Kingdom of Luang Phrabang which under their direction would acquiesce with their military presence and forestall a potential invasion by the Allies.
Background.
French Indochina comprised the colony of Cochinchina and the protectorates of Annam, Cambodia and Tonkin, and the mixed region of Laos. After the fall of France in June 1940 the French Indochinese government had remained loyal to the Vichy regime, which collaborated with the Axis powers. The following month governor Admiral Jean Decoux signed an agreement under which Japanese forces were permitted to occupy bases across Indochina. In September the same year Japanese troops invaded and took control of Northern Indochina, and then in July 1941 they occupied the Southern half as well. The Japanese allowed Vichy French troops and the administration to continue on albeit as puppets.
By 1944 with the war going against the Japanese after defeats in Burma and the Philippines they then feared an Allied offensive in French Indochina. The Japanese were already suspicious of the French; the liberation of Paris in August 1944 raised further doubts as to where the loyalties of the colonial administration lay. The Vichy regime by this time had ceased to exist, but its colonial administration was still in place in Indochina, though Decoux had recognized and contacted the Provisional Government of the French Republic led by Charles de Gaulle. Decoux got a cold response from de Gaulle and was stripped of his powers as governor general but was ordered to maintain his post with orders to deceive the Japanese. Instead Decoux's army commander General Eugène Mordant secretly became the Provisional Government's delegate and the head of all resistance and underground activities in Indochina. 
Prelude.
British intelligence—mission Force 136—air-dropped several Free French operatives into Indochina in late 1944. They provided detailed information on targets, mostly related to ship movements, along the coast to British headquarters in India and China, who in turn transmitted them to the Americans. During the South China Sea raid in January 1945 American carriers' aircraft sank twenty-four vessels and damaged another thirteen. Six U.S. navy pilots were shot down but were picked up by French military authorities and housed in the central prison of Saigon for safe keeping. The French refused to give the Americans up and when the Japanese prepared to storm the prison the men were smuggled out. The Japanese demanded their surrender but Decoux refused and General Yuitsu Tsuchihashi, the Japanese commander, decided to act. Tsuchihashi could no longer trust Decoux to control his subordinates and asked for orders from Tokyo. The Japanese High Command were reluctant for another front to be opened up in an already poor situation. Nevertheless, they ordered Tsuchihashi to offer Decoux an ultimatum and if this was rejected then at his discretion a coup would be authorised. With this coup the Japanese planned to overthrow the colonial administration and intern or destroy the French army in Indochina. Several friendly puppet governments would then be established and win the support of the indigenous populations.
Opposing forces.
French Army.
In early 1945, the French Indochina army still outnumbered the Japanese in the colony and comprised about 65,000 men, of whom 48,500 were locally recruited "Tirailleurs indochinois" under French officers. The remainder were French regulars of the Colonial Army plus three battalions of the Foreign Legion. A separate force of indigenous "gardes indochinois" (gendarmerie) numbered 27,000.
Despite superiority in number, since the fall of France in June 1940 no replacements or supplies had been received from outside Indochina. By March 1945, only about 30,000 French troops could be described as fully combat ready, the remainder serving in garrison or support units. French troops, since the collapse of their authority in Indochina, were exclusively used by the Japanese to suppress insurgencies by various nationalist movements in Vietnam, mainly the Việt Minh; the French had already developed a reputation of repressive behaviour toward the native population, which hindered any opportunity to recruit local support.
Japanese Army.
At the beginning of 1945, the understrength Japanese Thirty-Eighth Army was composed of 30,000 troops, a force that was substantially increased by 25,000 reinforcements brought in from China, Thailand, and Burma in the following months. Despite an initial disparity in numbers, the disciplined, well-equipped and battle-hardened Japanese troops enjoyed local superiority over their French counterparts even prior to the coup.
The coup.
Japanese ultimatum.
In early March 1945 Japanese forces were redeployed around the main French garrison towns throughout Indochina, linked by radio to the Southern area headquarters. French officers and civilian officials were however forewarned of an attack through troop movements, and some garrisons were put on alert. The Japanese envoy in Saigon Ambassador Shunichi Matsumoto declared to Decoux that since an Allied landing in Indochina was inevitable, Tokyo command wished to put into place a "common defence" of Indochina. Decoux however resisted stating that this would be a catalyst for an Allied invasion but suggested that Japanese control would be accepted if they actually invaded. This was not enough and Tsuchihashi accused Decoux of playing for time.
On 9 March, after more stalling by Decoux, Tsuchihashi delivered an ultimatum for French troops to disarm. Decoux sent a messenger to Matsumoto urging further negotiations but the message arrived at the wrong building. Tsuchihashi, assuming that Decoux had rejected the ultimatum, immediately ordered commencement of the coup.
Japanese attacks.
That evening Japanese forces moved against the French in every center. In some instances French troops and the "Garde Indochinoise" were able to resist attempts to disarm them, with the result that fighting took place in Saigon, Hanoi, Haiphong and Nha Trang and the Northern frontier. Japan issued instructions to the government of Thailand to seal off its border with Indochina and to arrest all French and Indochinese residents within its territory. Instead, Thailand began negotiating with the Japanese over their course of action, and by the end of March they hadn't fully complied with the demands. Dōmei Radio (the official Japanese propaganda channel) announced that pro-Japanese independence organizations in Tonkin formed a federation to promote a free Indochina and cooperation with the Japanese.
The 11th R.I.C ("régiment d'infanterie coloniale") based at the Martin de Pallieres barracks in Saigon were surrounded and disarmed after their commanding officer, Lieutenant-Colonel Moreau, was arrested. In Hue there was sporadic fighting; the "Garde Indochinoise", who provided security for the "résident supérieur", fought for 19 hours against the Japanese before their barracks was overrun and destroyed. Three hundred men, one third of them French, managed to elude the Japanese and escape to the A Sầu Valley. However, over the next three days, they succumbed to hunger, disease and betrayals - many surrendered while others fought their way into Laos where only a handful survived. Meanwhile, Mordant led opposition by the garrison of Hanoi for several hours but was forced to capitulate, with 292 dead on the French side and 212 Japanese.
An attempt to disarm a Vietnamese garrison ended badly for the Japanese when 600 of them marched into Quảng Ngãi. The Vietnamese nationalists had been armed with automatic weapons supplied by the OSS parachuted nearby at Kontum. The Japanese had been led to believe that these men would readily defect but the Vietnamese ambushed the Japanese. Losing only three killed and seventeen wounded they inflicted 143 killed and another 205 wounded on the Japanese before they too were overcome. A much larger force of Japanese came the next day but they found the garrison empty. In Annam and Cochinchina only token resistance was offered and most garrisons, small as they were, surrendered.
Further north the French had the sympathy of many indigenous peoples. Several hundred Laotians volunteered to be armed as guerrillas against the Japanese; French officers organized them into detachments but turned away those they did not have weapons for.
In Haiphong the Japanese assaulted the Bouet barracks: headquarters of Colonel Henry Lapierre's 1st Tonkin Brigade. Using heavy mortar and machine gun fire, one position was taken after another before the barracks fell and Lapierre ordered a ceasefire. Lapierre refused to sign surrender messages for the remaining garrisons in the area. Codebooks had also been burnt which meant the Japanese then had to deal with the other garrisons by force.
In Laos, Vientiane, Thakhek and Luang Prabang were taken by the Japanese without much resistance. In Cambodia the Japanese with 8,000 men seized Phnom Penh and all major towns in the same manner. All French personnel in the cities on both regions were either interned or in some cases executed.
The Japanese strikes at the French in the Northern Frontier in general saw the heaviest fighting. One of the first places they needed to take and where they amassed the 22nd division was at Lang Son, a strategic fort near the Chinese border.
Battle of Lạng Sơn.
The defences of Lạng Sơn consisted of a series of fort complexes built by the French to defend against a Chinese invasion. The main fortress was the "Fort Brière de l'Isle". Inside was a French garrison of nearly 4,000 men, many of them Tonkinese, with units of the French Foreign Legion. Once the Japanese had cut off all communications to the forts they invited General Émile Lemonnier, the commander of the border region, to a banquet at the headquarters of the 22nd division of the Imperial Japanese Army. Lemonnier declined to attend the event, but allowed some of his staff to go in his place. They were taken prisoner and soon after the Japanese bombarded "Fort Brière de l'Isle", attacking with infantry and tanks. The small forts outside had to defend themselves in isolation; they did so for a time, proving impenetrable, and the Japanese were repelled with some loss. They tried again the next day and succeeded in taking the outer positions. Finally, the main fortress of Brière de l'Isle was overrun after heavy fighting.
Lemonnier was subsequently taken prisoner himself and ordered by a Japanese general to sign a document formally surrendering the forces under his command. Lemonnier refused to sign the documents. As a result, the Japanese took him outside where they forced him to dig a grave along with French Resident-superior ("Résident-général") Camille Auphelle. Lemonnier again was ordered to sign the surrender documents and again refused. The Japanese subsequently beheaded him. The Japanese then machine-gunned some of the prisoners and either beheaded or bayoneted the wounded survivors.
The battle of Lạng Sơn cost the French heavy casualties and their force on the border was effectively destroyed. European losses were 544 killed, of which 387 had been executed after capture. In addition 1,832 Tonkinese colonial troops were killed (including 103 who were executed) while another 1,000 were taken prisoner. On 12 March planes of the US Fourteenth Air Force flying in support of the French, mistook a column of Tonkinese prisoners for Japanese and bombed and strafed them. Reportedly between 400 and 600 of the prisoners were killed or wounded.
On the 12th the Japanese then advanced further north to the border town of Dong Dang where a company of the 3rd Regiment of Tonkinese Rifles and a battery of colonial artillery were based. Following Lemonnier's refusal to order a general surrender, the Japanese launched an attack against the town. The French resisted for three days. The Japanese were then reinforced by two regiments from 22nd Division from Lạng Sơn and finally overran the French colonial force. Fifty-three survivors were beheaded or bayoneted to death.
Retreat to China.
In the North West General Gabriel Sabattier's Tonkin division had enough time to be spared an assault by the Japanese and were able to retreat northwest from their base in Hanoi, hoping to reach the Chinese