FORGOTTEN WAR, The War Between France and Thailand (1940-1941) 

By Jean Huon 

French missionaries tried to convert Siamese people since 1550 but without success. One century later, they established some missions, and a Siamese delegation came to France in 1684 and 1686; it was received by King Louis the XIV. Some ambassadors, military councilors, soldiers and Jesuits were sent into the country to curb the British influence. But a revolution at the end of the 17th century put an end to the French presence.

Both countries established new diplomatic relations in 1856. A few years later, the French settled in Indochina, namely in Tourane in 1858, and took control of the Mekong Delta between 1859 and 1867. The King of Cambodia accepted a protectorate of France in 1863, without the agreement of Siam which was holding sway over Cambodia. But this situation was accepted by a peace treaty signed on July 15, 1867.

France extended its colonization of the country by the conquest of the Red River Delta and of Hanoi in 1873. In 1887, the Indochinese Union was created with Tonkin, Annam, Cochinchina and Cambodia. Laos would join later, in 1893.

Few people know that a war happened in Indochina, between France and Thailand in 1940-1941. Tourist guides are silent on the subject, and tours of the city of Bangkok never show the Victory Monument built after the conflict. 

The Origins of Conflict

Siam resented the integration of Laos in the Indochinese Union. Many skirmishes happened on the border, and France sent a warship off Bangkok. Without any help from the British, Siam accepted this situation.

New incidents erupted in 1906 and 1907 because of new territorial claims concerning territories in Cambodia and in Laos. After a British mediation, some exchanges of land were made, and the problem was solved by an agreement in 1909.

During WWI, Siam joined the Allies in July 1917, and an expeditionary force of 1,284 volunteers was sent in France. They were mainly assigned to services such as drivers, medical service and ordnance. One hundred of them were trained as aircraft pilots.

After the War and for 20 years, no trouble occurred between France and Siam. In 1932, after a coup d’état, the King was forced to accept a constitutional regime. Lieutenant-Colonel Prajadhipok, also known as Phibun, became the leader of the country. He was a former cadet of the French Military Academy and an admirer of Mussolini. He established a strong, nationalist, authoritarian government. He changed the name of the country of Siam into “Thailand” and claimed the incorporation to Thailand of all Thai people living in Burma and Laos. After discussions with France, a no-aggression agreement was reached and signed on June 12, 1940.

Hostilities

After the disaster of June 1940 and the defeat of France, Thailand expressed again territorial claims. Japan was probably part of this scheme. Japan issued an ultimatum to the French to allow the Japanese Army to march through Tonkin and take the control of the railway between Hanoi and the Chinese border. General Catroux, commanding the French Army in Indochina declined, but he was dismissed by the Vichy French government and replaced by Admiral Decoux. 

Decoux reached an agreement on September 22, 1940, with the Japanese. They were allowed to use French air bases and set up 6,000 men on the Northern bank of the Red River. On the same day in the evening, 30,000 Japanese soldiers invaded Indochina. Despite the resistance of the French, 4 days later, the Japanese occupied the country. But strangely, the French administration remained in place. 

During this time in Thailand, Phibun became general and prime minister, setting up an authoritarian policy. 

He believed that he could take advantage of the weakness of France to send an ultimatum to the government of Vichy, claiming the territories lost during King Chulalongkorn’s reign: Melou Prei and Tonle, Repou in 1904; and Battambang, Sisophon and Siem Reap in 1907. 

In November 1940, taking advantage of the French being busy quelling a rebellion among peasants, Thai Armed Forces crossed the Cambodian border on several locations. The Thai Air Force dropped bombs on Thatket and Savannakhet in Laos. After December 1, new incidents happened in Cambodia: bombing and artillery shelling. In retaliation, several Thai air bases were attacked by the French Air Force. 

In January 1941, Thai forces attacked both Cambodia and Laos. They invaded Yang Dang Khum and Phum Preav, and the French forces reeled back. Admiral Decoux set up a counter-attack with the 5th French Foreign Legion Infantry regiment on January 16. Several Thai villages were taken, but the troops could not hold on the battlefield. Thai tanks tried to pursue but were stopped by an anti-tank gun. 

Admiral Terreau, the French Navy commander, received the order to set up urgently a naval force. He rallied all the warships available: the Lamotte-Picquet cruiser, the Dumont d’Urville, Amiral Charner, Tahure and Marne corvettes. Its commander was Captain Bérenger. He attacked the superior Thai fleet in the Koh Chang Gulf. After 2 hours, the torpedo boats Songhkla, Chonburi and Trad were sunk; the Donburi and Sri Ayudhya armoured gunboats, severely damaged. 

End of the War and the Japanese Mediation 

On January 19, 1941, the Thai Army reached the South of Laos, and Angkor was bombed. One day later, Japan imposed its mediation. On January 30, an armistice was signed in Saigon, and hostilities stopped for 2 weeks. The troops had to pull back 6 miles from the frontline. 

Negotiations were opened in Tokyo on February 7. At first, the French delegation rejected the Thai claims. But at that moment, Admiral Darlan became the head of the Vichy government, favoring cooperation, and it had to submit. 

A peace treaty was signed on March 11; Thailand recovered the territories given to France: Battambang, Siem Reap, Kampong Thom and Stung Treng in Cambodia; Sayabouri and Champasak in Laos. 420,000 people and 19,000 square miles were involved. The monarchs of Cambodia and Laos were not even consulted! The territories annexed by Thailand were returned to France only on November 1947.

Retaliation

These annexations and the growing Japanese influence had a negative influence on the relations between Japan and the United States, which declared an embargo on steel and oil sales to Japan.

Meanwhile, the American secret services and the British set up a local resistance against the Japanese called “Seri Thai.”

Epilogue

After the war between France and Thailand, Japan invaded Cambodia and demanded to march through Thailand into Malaysia and Burma.

Without any answer from the Thai government, Japan invaded Thailand. Despite the resistance of the Thai Army, the government was forced into an agreement with Japan, and an alliance treaty was signed on December 21, 1941. Thailand declared war on Great Britain and on the United States on January 25, 1942. The Thai troops clashed with the British in Burma. A resistance was organized by the OSS.

At the end of war, the government of Thailand was overthrown and Phibun stepped down . He was arrested by the Allies as a war criminal, but could not be put in court because of a strong popular support; he was ultimately released.