The Japanese invasion of Thailand

On the night of 7–8 December 1941 Japanese transports dropped anchor off several towns on the east coast of the Malay Peninsula that belonged to Thailand, while at the same time columns of the Japanese Imperial Guards crossed the border from French Indochina. Thailand was a neutral state, and the Japanese ultimatum had been delivered only a few hours earlier. At Prachuap Khiri Khan, Chumphon, Nakhon Si Thammarat, Pattani and Songkhla, which the British and Japanese called Singora, Thai soldiers, policemen, airmen and schoolboys from the military youth training corps held out against the landings for several hours. The fighting was stopped only by an order from Bangkok: the government of Field Marshal Plaek Phibunsongkhram, known as Phibun, concluded that the country could not defend itself and agreed to let Japanese troops pass through to Malaya and towards the Burmese border. Two weeks later Thailand was already Japan’s ally.

War chronologies often list these events twice: under 7 December the invasion of Thailand appears among the objectives of the Japanese offensive, and under 8 December “the Battle of Prachuap Khiri Khan”. Both entries refer to the same operation. The date of 7 December follows the American calendar; in Thailand, where clocks were then seven hours ahead of Greenwich, the landings began on 8 December, most of them a few hours after midnight, at roughly the same time as the raid on Pearl Harbor or shortly after it.

A state between empires

Thailand, known until 1939 as Siam, was the only country in South-East Asia that had not become a colony. In the nineteenth century it owed this to the skill of its kings and to the fact that Britain and France preferred to have a buffer state between Burma and Indochina. From 1938 it was ruled by Phibun, a nationalist fascinated by Mussolini and by Japan’s modernisation. When France lost the war in Europe and the Japanese moved into northern Indochina, Phibun laid claim to the lands lost to the French at the turn of the twentieth century. He lost the naval battle of Ko Chang, but Japan imposed an armistice on both sides and, by the Treaty of Tokyo of 9 May 1941, awarded Thailand western Cambodia and the Laotian lands on the right bank of the Mekong. This “mediation” came at a price: according to some historians, Phibun was already then, in his talks with the Japanese, not ruling out letting their troops pass through in the event of war with the British.

At the same time Phibun feared that Japan, whose troops had stood in southern Indochina since July 1941, would swallow his country as well. He therefore sought insurance in the West. In June 1940 Thailand concluded a non-aggression pact with Britain, and in 1941 Bangkok asked London and Washington several times whether it could count on real help in the event of a Japanese attack. No one gave such a promise. Winston Churchill was prepared to warn Japan publicly that an attack on Thailand would mean war with Britain, but he did not want to do so without the Americans, and they did not want to commit themselves. The Thai army numbered about 26,000 men in peacetime and about 50,000 once the reserves were mobilised; the air force had some 150 combat aircraft, many of them obsolete. Against the two Japanese armies standing in Indochina it had no chance.

Thailand was indispensable to Japanese plans. Lieutenant General Tomoyuki Yamashita’s 25th Army, which was to take Malaya and Singapore, needed Thai ports on the Kra Isthmus, because the best roads and the railway to the west coast of Malaya ran from there. Lieutenant General Shōjirō Iida’s 15th Army was to cross the plain around Bangkok, secure the country and prepare a thrust into Burma. Planners in Tokyo, among them Lieutenant Colonel Masanobu Tsuji, had long studied the Thai coast. They expected Bangkok to give way under pressure and the troops to pass through without a fight, but they did not intend to make the timing of the operation depend on it: the landings were to take place on the same night as the attack on Malaya, whatever the government’s answer. The order to start the war, “Niitakayama nobore”, was issued on 2 December, and the invasion convoys sailed on 4 December from Hainan and from the ports of Indochina.

The ultimatum

In the last days of peace the British already knew that Japanese convoys were heading towards the Gulf of Thailand. On 7 December Churchill sent Phibun a telegram which, according to some accounts, reached Bangkok only after the Japanese landings: “There is a possibility of an imminent Japanese invasion of your country. If you are attacked, defend yourselves. The preservation of Thailand’s true independence and sovereignty is in Britain’s interest, and we shall regard an attack on you as an attack on ourselves.” These words had no force behind them: the British plan “Matador”, which provided for troops from Malaya to enter southern Thailand ahead of the Japanese, was never carried out.

At about 11 p.m. on 7 December the Japanese ambassador in Bangkok, Teiji Tsubokami, demanded that the Thai foreign minister, Direk Jayanama, consent to the passage of Japanese troops through the country. He was given two hours. The minister replied that only the prime minister could take the decision, and the prime minister was not in the capital. Phibun was in the east of the country, near the border with Indochina, and according to most accounts reached Bangkok only at about 7 a.m. Historians still argue over whether his absence that night was chance or the ploy of a man who wanted to avoid responsibility for capitulation, or who was waiting for the situation to resolve itself. The ultimatum expired unanswered, and the Japanese units, which were already off the coast in any case, began to go ashore.

Landings on the isthmus

The most important objectives lay in the south, close to the Malayan border. At Songkhla three regiments of Lieutenant General Takuro Matsui’s 5th Division landed, carried in ten transports and covered by destroyers; Yamashita himself was with them with his staff. The local garrison, an infantry battalion and an artillery battalion, took up positions on the roads leading south, but the Japanese bypassed it and set off for Hat Yai, a railway junction inland. According to Thai tallies, a dozen or so Thai soldiers were killed around Songkhla and Hat Yai. At Pattani a regiment of the 5th Division landed in rough seas on a beach backed by a treacherous, soft seabed; under fire from a Thai battalion, the police and youths of the military youth training corps from the local school, the landing force was long unable to move off the shore. The battalion commander, Khun Inkhayutboriharn, was killed, and with him, according to Thai figures, several dozen soldiers, policemen, schoolboys and civilians.

Further north, units of the 143rd Infantry Regiment of the 55th Division, which was subordinate to the 15th Army, came ashore. At Nakhon Si Thammarat, headquarters of the Thai 6th Division, the Japanese landed right next to the main military camp, and the fighting went on until noon. At Chumphon a Japanese battalion was pinned to the beach by an infantry battalion, the provincial police and a detachment of the Yuwachon Thahan, the “young soldiers”, secondary-school pupils with military training. Their commander, Captain Thawin Niyomsen, was killed and posthumously promoted to lieutenant colonel. The memory of the teenagers defending the bridge at Chumphon later became an important part of the Thai story of that day. At Surat Thani a Japanese company was held back in pouring rain by the police, supported by volunteers from the town.

The longest resistance came at Prachuap Khiri Khan, home of the 5th Wing of the army air force. A Japanese battalion landed at about 3 a.m., took the town after breaking the resistance of the police, and surrounded the airfield. Airmen, mechanics and policemen fought as infantry all day and all night, and the order to cease fire reached them only at noon on 9 December. According to Thai figures, 37 defenders were killed. Japanese losses are uncertain: Japanese estimates speak of more than a hundred dead, Thai estimates of more than two hundred. It is this fighting that is sometimes called “the Battle of Prachuap Khiri Khan”, and in Thailand it is commemorated every year with a ceremony on the grounds of the former base.

On the central plain, meanwhile, there was no fighting. Lieutenant General Takuma Nishimura’s Imperial Guards Division crossed the border at dawn near Battambang, in lands that Thailand had recovered only a few months earlier, and advanced on Bangkok. A Guards battalion that landed early in the morning at Samut Prakan, at the mouth of the Chao Phraya (Menam), ran into the Thai police; there was a tense confrontation, but no shots were fired, and the Japanese agreed to wait for the outcome of negotiations before entering the capital. Japanese aircraft attacked Don Mueang airfield near Bangkok, where the Thai air force lost several fighters. In the south, on the Malayan border, the Thai police in turn fired on British columns that had entered the country at the last moment to delay the Japanese. All this fighting, against the Japanese and against the British, cost Thailand about 180 dead according to Thai tallies.

The decision in Bangkok

When Phibun reached the capital in the morning, the cabinet had already been in session for several hours. Some ministers, among them the finance minister Pridi Banomyong, Phibun’s former comrade from the revolution of 1932, favoured resistance, even the departure of the government and its re-establishment in exile. The majority concluded, however, that the army could not stop the Japanese and the British would not help it. Phibun cut the discussion short, and according to those present the decision to cease fire was taken at about 7.30 a.m. It was several hours before the order reached the distant garrisons on the Kra Isthmus, and at Prachuap Khiri Khan more than a day. On the same day – on 9 December according to some sources – Thailand and Japan signed an agreement on passage: Japanese troops could cross the country and use its ports, airfields and railways, and Japan promised to respect Thai independence and sovereignty.

Phibun presented this decision to his compatriots as the only way of saving the state from the fate of the occupied countries and, according to some accounts, also as a step agreed beforehand with a Japanese government well disposed towards Thailand. In the afternoon Japanese troops entered Bangkok, and within a few hours Japanese squadrons flew in from Indochina to the airfield near Songkhla, from which they could now bomb the British airfields in northern Malaya at close range. From the capital the Guards set off south by rail and road to join the 25th Army.

From passage to alliance

Consent to passage was only the beginning. Japan’s victories in the first days of the war – the sinking of the British warships off Kuantan and the rapid advance in Malaya – convinced Phibun that Japan would win. According to some historians, a secret military agreement was concluded on 14 December providing for Thai troops to take part in operations against the British. On 21 December 1941, in the Temple of the Emerald Buddha in Bangkok, Phibun and Ambassador Tsubokami signed a treaty of offensive and defensive alliance. In a secret protocol Japan undertook to help Thailand recover the lands lost to the British, and Thailand placed its railways, roads, ports, airfields, depots and barracks at the disposal of the Japanese. Opponents of this policy left the government: in mid-December Pridi became a member of the regency council acting for the young King Ananda Mahidol, who was living in Switzerland, which removed him from day-to-day politics.

Thailand’s path alongside Japan did not end there. After British air raids on Bangkok in January 1942, Phibun’s government declared war on Britain and the United States on 25 January 1942. The Thai minister in London delivered the declaration to the British, but the minister in Washington, Seni Pramoj, an aristocrat and avowed opponent of Japan, refused to deliver it. He held that it did not express the will of the nation, and the State Department decided to go on treating him as Thailand’s representative. The United States never declared war on Thailand. Among Thai students in America Seni began to organise the Seri Thai, the “Free Thai” movement, which worked with American intelligence. At home the underground network was directed by the regent, Pridi.

Place in the war

The invasion of Thailand lasted a few hours and was the least bloody of Japan’s operations of 8 December, but it was of great importance for the whole campaign. Without the Thai ports and airfields Yamashita would have had to land solely on the strongly defended beaches of Malaya; thanks to them his main forces came ashore almost without loss and from the first day had a secure rear, a railway and airfields behind them. It was through Thailand that the 15th Army struck at Burma in January 1942, and Thai airfields were used to bomb Rangoon. Later the Japanese drove the Burma Railway through the Thai jungle, built by Allied prisoners of war and Asian forced labourers, tens of thousands of whom died.

For Thailand itself the alliance proved costly. The country kept its own government, army and administration and was not formally occupied, but at the peak some 150,000 Japanese troops were stationed there, behaving more and more like occupiers. In 1942 the Thai army, together with the Japanese, occupied part of the Shan States of Burma, and in 1943 Tokyo handed Thailand four sultanates of northern Malaya. Inflation, requisitions and Allied bombing undermined Phibun’s position, and in July 1944 he was forced to step down. After Japan’s surrender the regent Pridi proclaimed the declaration of war of 1942 null and void, as contrary to the will of the nation and to the constitution. Thanks to Seni Pramoj’s stance and the activity of the Free Thai, the United States did not treat Thailand as a defeated enemy, and the British contented themselves with the return of its territorial gains and deliveries of rice. Thailand also returned to France the lands it had won in 1941. It came out of the war without occupation and without losing its independence, and Phibun, tried after the war for collaboration with Japan and released, became prime minister again in 1948.