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The Franco-Thai War (1940-1941)

by Pierre To
13 minutes to read
Admiral Jean Decoux Franco-Thai war

The Franco-Thai War was fought between the Thailand of General Plaek Pibulsonggram, known as Phibun, and the Vichy French forces in the Indochinese peninsula.

This war preceded the outbreak of the Pacific War proper by a few months.

Negotiations with France before World War II had shown that the French government was willing to make minor changes in the boundaries between Thailand and French Indochina.

After the defeat of France in 1940, Major-General Plaek Pibulsonggram, Prime Minister of Thailand, decided that the situation gave the Thais an even better chance to regain the territories lost during the reign of King Chulalongkorn.

The context of the Franco-Thai War

General Plaek Pibulsonggram, known as Phibun

General Phibun

On 12 June 1940, the Thai government had agreed to sign a non-aggression pact with France, but after the French rout of 1940, Thai Prime Minister Phibun saw a chance for Thailand to recover the territories abandoned to France during Chulalongkorn's reign and to avenge the humiliations suffered in 1893 (attachment of Laos to French Indochina) and 1904.

The provinces in question are Melou Prei and Tonlé Repou in 1904, and the provinces of Battambang, Sisophon and Siem Reap in 1907, which were ceded in 1867 in exchange for the recognition of the protectorate over the Khmer kingdom; these provinces were all attached to Cambodia,)

The weakening of the metropolis made the maintenance of French control over Indochina hazardous and difficult.

The colonial administration, deprived of aid and reinforcements, had been forced to allow the Japanese to settle in French Indochina after the capture of Lạng Sơn (offensive of 22-25 September 1940).

The weak French resistance to the invasion convinced the Phibun regime that a military confrontation would work to its advantage.

The forces at work

The French forces in Indochina consisted of an army of approximately 60,000 men, 12,000 of whom were from metropolitan France (and served in the so-called 'sovereignty' regiments), organised into 41 infantry battalions, two artillery regiments, and an engineer battalion.

The most obvious weakness of the French army was its lack of tanks: it could field only 20 Renault FT-17s compared to 134 for the Thai army.

Renault FT-17 tank

Renault FT-17 tank

The Vichy air force in Indochina consisted of about one hundred aircraft, of which about sixty could be sent to the front line: 30 Potez 25s, four Farman 221s, six Potez 542s, nine Morane-Saulnier M.S.406s and eight Loire 130s.

The Thai army was relatively well equipped. It consisted of about sixty thousand men, divided into four armies, the largest being Burapha's army with five divisions.

The independent formations under the direct authority of the army high command included two motorised cavalry battalions, an artillery battalion, a signal battalion, an engineer battalion and an armoured regiment.

The artillery had at its disposal a mixture of old Krupps, modern Bofors howitzers and field mortars (pistols?), while sixty Carden-Loyd trackers and thirty Vickers 6-Tons made up the armour.

The Thai air force and navy had received attention from the Thai government in the 1930s.

The Royal Thai Air Force had about 200 combat aircraft and 120 training aircraft.

The American embargo of October 1940 had pushed Bangkok to obtain more supplies from Japan: during the winter of 1940, the country received 33 Nakajima Ki-27 and 9 Mitsubishi Ki-21-I bombers, as well as about thirty Mitsubishi Ki-30s.

However, it hired older models instead, notably Martin B-10s.

The navy had about 30 units, including two Japanese-built battleship coastguards, the Thonburi and the Sri Ayuthaya (armed with four 203 mm calibre guns), nine Italian-built torpedo boats (equipped with six 533 mm torpedo tubes) and four coastal submarines (delivered in 1938 by Japan).

It also had a small anti-submarine air force and two marine battalions.

Triggering operations

After nationalist and anti-French demonstrations in Bangkok, border skirmishes followed along the Mekong.

The Thai air force, superior in number, bombed Vientiane, Sisophon and Battambang during the day with impunity.

The French air force attempted retaliatory raids, but the damage caused to Thailand was much less.

Admiral Jean Decoux, Governor General of Indochina, acknowledged that the Thai airmen flew like men with several campaigns under their belt. In December 1940, Thailand occupied Pak-Lay and Champassak Province.

In early January 1941, the Burapha Thai and Isaan armies launched an offensive on Laos and Cambodia.

French resistance was immediately in place, but many units were outnumbered by the better equipped Thai forces.

The Thais quickly occupied Laos, while in Cambodia the French resistance was more effective.

On 16 January, France launched a large counter-offensive led by the 5th Foreign Infantry Regiment on the Thai villages of Yang Dang Khum and Phum Préav, where the fiercest fighting of the war took place.

The French counter-attack was blocked and ended in a retreat, but the Thais were unable to pursue the French forces as their tanks were pinned down by French anti-tank guns.

The Battle of Koh Chang

While the situation on land was critical for France, the Governor General of Indochina, Admiral Jean Decoux, gave permission to Admiral Jules Terraux, commander of the French Navy in French Indochina, to carry out an operation against the Thai Navy.

The French fleet in Indochina was then heterogeneous. An "occasional group" was formed with the light cruiser La Motte-Picquet as flagship, the colonial avisos of the Bougainville Dumont d'Urville and Amiral Charner classes, and the old avisos Marne and Tahure.

This fleet was placed under the command of Captain Régis Bérenger, commander of the La Motte-Picquet.

The French force had several seaplanes: 2 Loire 130, one of which was left in Saigon by the Suffren for the needs of the operation, 3 Potez 452, 2 of which were embarked by the La Motte-Picquet, 3 Gourdou 832, 2 of which were launched by the colonial avisos.

Although obsolete, these seaplanes were to play a key role in the battle by pinpointing the location of the Thai ships at Koh Chang.

Five river gunboats accompanied the fleet but did not participate in the battle.

The light cruiser La Motte-Picquet

The light cruiser La Motte-Picquet

The Thai fleet is composed of the two battleships Sri Ayuthia and Dhomburi, ten torpedo boats, of which 9 are modern Italian-made, one is old British-made, two avisos, one submarine, two mine sweepers.

Available French warships are ordered to attack in the Gulf of Thailand.

An aerial reconnaissance is carried out on 16 January at Satahib (eastern tip of Bangkok Bay) and Koh Chang.

The French fleet leaves the island of Poulo Condor on January 15. It crossed the Gulf of Siam, and surprised a squadron of the Thai fleet at anchor at dawn on 17 January.

The Thai ships tried to take advantage of the multitude of islets that protected the Koh Chang sea base, but the French units blocked the exit channels and shelled them from several sides.

At the end of the fight, which lasted just under two hours, the toll was high on the Thai side.

One third of its fleet was out of action. The torpedo boats Chonburi, Songhkla and Trad, built in Italy between 1935 and 1937, were sunk (Trad was later refloated and put back into service).

The battleship Dhomburi is badly hit and eventually capsizes on the Chantaboum bar. Her sister-ship Sri Ayuthia was torpedoed by La Motte-Picquet.

Of the three torpedoes launched, only one hits, but forces the ship to run aground to avoid sinking.

These two battleship units were built in Japan in 1937 and 1938 and were armed with 203 mm twin turrets.

The official death toll on the Thai side is 36 men (including the Thonburi commander), but the figures are probably higher, probably 300 men were killed.

Several Japanese officers on board the Siamese ships were also reportedly killed in the clash.

The French fleet returned to Saigon almost intact. No one was killed, a few were wounded and there was only minor material damage.

Naval historian Jacques Mordal has pointed out that the Battle of Koh Chang was the only naval battle fought and won in both world wars by a French naval force, using exclusively French plans and resources.

In his war memoirs, General de Gaulle recalls 'the brilliant naval victory of 17 January 1941 during which the cruiser La Motte-Picquet and a few French avisos sent the Siamese fleet to the bottom'.

Following this victory, Captain Régis Bérenger was promoted to Rear Admiral.

However, this feat of arms remains unknown in France, perhaps because it was won by the Vichy Navy.

Nevertheless, the name of this battle can be found in a few streets and squares and some memorials in Brittany and the Vendée.

Conclusion and consequences of the Franco-Thai War

The toll of the war differs according to the sources. Some mention about 3,400 dead.

Japan, eager to secure Thailand's military cooperation, quickly intervened as a mediator in the conflict.

An ultimatum first imposed an armistice on the two belligerents, which was proclaimed on 28 January. On May 9, France, under Japanese pressure, signs a peace treaty, by which it abandons the provinces of Battambang and Siem Reap, taken from Cambodia, Champassak and Sayaburi (taken from Laos, which thus cedes the territories on the right bank of the Mekong), i.e. a territory of more than 50,000 km2 inhabited by 420,000 people.

This treaty is followed by another between France and Laos on 21 August.

This annexation provoked, in July 1941, the imposition by the United States of an embargo on oil deliveries to Japan and the creation, with the help of the Anglo-Saxon secret services, of the Thai Seri (Free Thais), a clandestine anti-Japanese organisation.

The Thai government orally promises the Japanese passage through its territory as part of the Empire's planned attack on Malaya.

On 8 December 1941, as Thailand had still not responded to Japanese demands, Japan decided to override them and, in order to pass into Malaya, invaded Thailand's territory.

The invasion ended with the battle of Prachuab Khirikhan and a ceasefire a few hours later, and Thailand allied itself with Japan.

The territories annexed by Thailand were not returned to France until November 1947, but were not retained for long, as the Indochina territories gained independence shortly afterwards.

The weakness that France revealed is one of the factors of this decolonisation.


The French army had a total of 321 killed, of which 15 were officers. After 28 January, it had 178 missing (6 officers, 14 NCOs, and 158 enlisted men).

The Thais captured 222 men (17 North Africans, 80 French, and 125 Indochinese).

The Thai army had a total of 54 killed and 307 injured. 41 Thai Navy sailors and soldiers were killed, and 67 wounded.

At the Battle of Ko Chang, 36 men were killed, including 20 crew members from HTMS Thonburi, 14 from HTMS Songkhla, and 2 from HTMS Chonburi.

The Thai Air Force lost 13 men. 21 Thai soldiers were captured by the French.

About 30 %s of French aircraft had been rendered unserviceable by the end of the war, some of it due to minor, unrepaired air raid damage.

The Vichy Air Force admitted the loss of one Farman F221 and two Morane-Saulnier MS.406 destroyed on the ground, but in reality its losses were greater.

In its first combat experience, the Royal Thai Air Force claimed to have shot down five French aircraft in the air and destroyed seventeen on the ground, for the loss of three of its own aircraft in the air and five to ten destroyed in French air raids on Thai airfields.

Video on the Franco-Thai War

The news of the time talking about the war:

Source: wikipedia.org/

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