Seri Thai: Thailand’s Secret War Against Japan

On the morning of 8 December 1941, shortly after the bombing of Pearl Harbor, Japanese troops swept ashore at several points along the Thai coast. They were moving quickly through Southeast Asia, and Thailand stood directly in their path. Thai military and police units resisted the landings in several areas, but the fighting was brief. Within hours, the government ordered its forces to cease fire, and Thailand found itself facing a new reality. The Japanese were not passing through as a temporary invading army. They were going to stay.

Field Marshal Plaek Phibunsongkhram’s government quickly fell into line. Thailand entered into an alliance with Japan, and cooperation with the Japanese war effort became official policy. To the outside world, it appeared that Thailand had chosen its side. But that wasn’t the whole story.

Behind the official government position, opposition to the Japanese was already beginning to form. Pridi Banomyong, one of the country’s most influential political figures and Regent to a young King, was determined that Thailand should not simply become a Japanese satellite and then be treated as an enemy nation when the war was over. What followed was one of the most remarkable underground movements of the Second World War.

It would involve politicians and soldiers, policemen and students, radio operators and secret agents. Weapons would be hidden in the countryside, Allied equipment would arrive by parachute, and men would disappear into the mountains to train for a war that might never come. Some members would risk their lives gathering intelligence for Allied aircraft, while others would help Allied agents enter and leave the country.

One of Thailand’s most powerful police officers would secretly protect the very people his government was supposed to be hunting, while somewhere in the mountains of northeastern Thailand, a resistance force would prepare for the day when it might have to fight the Japanese openly. That movement would become known as Seri Thai, the Free Thai.

The Resistance Takes Shape

The Japanese invasion had barely begun when opposition to the new alliance started taking shape. Pridi and others who disagreed with the government’s decision began organising what was initially an anti-Japanese movement.

Overseas, Thai students and officials were doing much the same thing, particularly in the United States and Britain. The movement was never a conventional army. It was a network, and its members had very different jobs.

Some gathered intelligence, while others operated radios or helped Allied agents. Some received military training overseas before finding their way back into Thailand, while others organised local groups and prepared hidden bases. The Americans supplied training and equipment through the OSS, while British Force 136 became deeply involved in the movement in Thailand.

The overseas network was important for another reason: Thailand had to convince the Allies that there was a genuine resistance movement inside the country and that not every Thai supported the government’s alliance with Japan.

This became increasingly important as the war progressed. In Britain, the Free Thai effort also had a royal connection. Queen Rambai Barni, the former queen consort of King Prajadhipok, was living in England and became involved in supporting the Thai resistance there. Her role was part of a wider overseas effort that included Thai students, officials and volunteers working with the British.

Meanwhile, inside Thailand, the movement had to operate under the noses of the Japanese.And one of its greatest advantages was something the Japanese could never completely control: the Thai state itself.

The Policeman at the Top

Adul Aduldecharat, better known as Luang Adul, occupied an extraordinary position. He was Commissioner-General of the Royal Thai Police, the highest-ranking officer in the country’s police force.

He was also a general in the Thai armed forces, Deputy Prime Minister and Deputy Minister of the Interior. He was not some minor official quietly helping the resistance from the sidelines. Adul was one of the most powerful men in Thailand.

To the Japanese, and to much of the Thai public, he could appear to be exactly what the government required: a rigid and uncompromising law enforcer carrying out the policies of Phibun’s administration. Behind that public role, however, Adul was secretly helping the Seri Thai movement and working closely with Pridi.

His position gave him an extraordinary weapon. The police controlled much of the country’s internal security and intelligence apparatus, including the people who might discover Allied agents or Thai resistance members operating illegally.

When Allied personnel or Seri Thai operatives were reported or discovered, Thai police could sometimes reach them before the Japanese did. Instead of immediately handing them over, they could place them in Thai custody, where they were effectively protected.

It was an extraordinarily dangerous double game. Adul had to maintain the appearance of a loyal government official while secretly ensuring that some of the people the Japanese wanted to find remained alive and connected to the resistance.

The Japanese were suspicious. They knew that Allied agents were operating in Thailand and that something was happening behind the official cooperation between the two countries, but the very machinery they relied upon to investigate those activities could be manipulated from within.

Adul was sitting at the top of it.

The American Pilot Who Wasn’t Supposed to Survive

One of the clearest examples of what this meant involved an American pilot named William “Black Mac” McGarry. In March 1942, during an air raid over Chiang Mai, McGarry’s P-40 Warhawk was hit by anti-aircraft fire. He managed to keep the damaged aircraft flying towards Mae Hong Son before the engine finally failed and he was forced to bail out into the jungle.

He survived for weeks in the wilderness before being found by local Thai police. Under normal circumstances, the discovery of an American airman in Japanese-aligned Thailand could have ended very badly. Instead, McGarry was taken into Thai custody and eventually brought to Bangkok, where he remained alive for the next three years in a country where the Japanese would certainly have been interested in questioning him.

Adul personally helped coach McGarry and other Allied prisoners on how to deal with Japanese questioning. They had to know what to say and, just as importantly, what not to say, so that the Japanese would have no excuse to take complete control of the prisoners.

By early 1945, American intelligence officers working with the Seri Thai network had established themselves in Bangkok. General Claire Chennault, the famous commander associated with the Flying Tigers, wanted to know whether McGarry was still alive. The answer came back remarkably quickly: he was alive, and the OSS believed they could get him out.

The rescue required an elaborate deception. Thai officials reported that McGarry had died, while the details of how he was removed from captivity vary between later accounts. One version describes him being concealed in a coffin and smuggled out under the cover of a fabricated death. Whatever the precise mechanics, the operation succeeded.

On 14 April 1945, McGarry was brought out of captivity and eventually taken down the Chao Phraya River towards the Gulf of Thailand, where an American Catalina flying boat was waiting to take him to safety in British Ceylon.

The Japanese were furious when they discovered that the American prisoner had disappeared, but they could not easily determine exactly how it had happened. The man officially responsible for keeping an American prisoner under control had helped engineer his escape.

Into the Mountains

While Adul and others were protecting the resistance within the machinery of the Thai state, another part of Seri Thai was preparing for a very different kind of war.

In the Phu Phan Mountains of northeastern Thailand, Tiang Sirikhan became one of the leading figures in the regional movement. The mountains provided exactly what a clandestine organisation needed: difficult terrain, forests, isolated communities and plenty of places where weapons, radios and people could disappear from sight.

Training camps were established, weapons were hidden, radio facilities were created and secret airfields prepared. Allied equipment was delivered by parachute, giving the movement the means to train and potentially fight on a much larger scale. The preparations were serious enough to support a major uprising if the Allies launched an operation to liberate Thailand, and the wider movement eventually organised cadres across much of the country.

But the Phu Phan network was not simply a guerrilla army roaming the countryside looking for Japanese patrols. Much of its work was intelligence gathering, communications, recruitment, training and concealment of Allied equipment. The mountains were primarily a secure base from which a larger resistance operation could be launched if circumstances demanded it, and sometimes the Japanese came dangerously close to discovering what was there.

The Hidden Airfield

One of the secret airfields in the region had been disguised so effectively that it appeared to be ordinary agricultural land. In August 1945, Japanese troops searching for the landing area took a local headman hostage and forced him to guide them towards the suspected location. Accounts of the incident describe the Japanese searching the area without discovering the concealed airfield.

The situation could easily have turned into a gunfight, but the Japanese eventually withdrew and the incident ended without bloodshed. It was a small victory, but it demonstrated one of the most important strengths of the Seri Thai movement. Its survival depended as much on secrecy, deception and local cooperation as it did on guns. The Japanese could search the mountains, but they did not always know what they were looking for.

A War Fought by Radio

Elsewhere, Seri Thai agents were fighting a very different kind of war. In the Phrae area, informants were positioned near Japanese bases and collected information about Japanese military positions. The information was transmitted by Morse code to American forces, helping Allied aircraft identify targets more accurately.

The Seri Thai also provided warnings about villages and civilian areas so that Allied agents could avoid putting local people unnecessarily at risk. This was sabotage of a different kind. The resistance did not always need to plant explosives themselves. By identifying Japanese installations and passing accurate information to the Allies, they could make an Allied bombing raid more effective.

The wider Free Thai network established radio stations and systematic intelligence operations during the later stages of the war, passing information about Japanese troop movements and other military matters to Allied bases in India and Ceylon.

This mixture of intelligence, communications and military preparation was typical of Seri Thai. It was a movement that could look very different depending on where you encountered it; a secret radio operator in one place, an armed group hidden in the mountains in another, or a policeman at the very top of the security establishment in Bangkok.

The Man Who Fell From the Sky

The story of Puey Ungphakorn provides another glimpse of just how dangerous these operations could be. Puey had joined the Free Thai effort and was actually a commissioned officer in the British Army. Some sources have suggested that his mission carried more than military instructions, and that he was also carrying a message concerning British cooperation with the Free Thai movement, authorised by Winston Churchill and passed through Lord Mountbatten, the British Commander-in-Chief in Southeast Asia.

According to this account, Puey ultimately delivered the message to Pridi at his residence in Bangkok in the dead of night, giving Puey’s meeting with him an important political as well as military significance.

Whatever the precise details of the mission, Puey’s journey had already gone badly wrong. He was parachuted into the wrong area, was discovered and beaten by locals, before eventually being handed over to local police and sent to Bangkok. Instead of disappearing into Japanese custody, however, he found himself under the control of Adul.

Several sources have suggested that Adul allowed Puey and other captives a remarkable degree of freedom during the night, giving them opportunities to carry out clandestine activities while maintaining the appearance that they remained prisoners.

The episode shows how valuable Adul’s position was. He did not have to operate from a jungle camp; he could manipulate the system around the prisoners while the Japanese remained uncertain about what was happening. The resistance was not simply hiding from the Japanese. Parts of it were hiding inside the Thai authorities themselves.

Waiting for the Uprising

By 1945, the Seri Thai had built a substantial organisation. It had trained men, weapons, radio communications, Allied contacts and hidden bases. In the Phu Phan region, the movement was prepared for the possibility of a major armed uprising, while Pridi was increasingly concerned that Japan might surrender before the Seri Thai had demonstrated its willingness to fight.

If that happened, Thailand could be left looking like a Japanese ally that had done little to resist the occupation. On 20 May 1945, Pridi sent a message to the American Secretary of State asking for Allied approval for the Free Thai to rise openly against the Japanese. The Allies withheld permission and asked him to wait until the time came for a larger Allied operation.

The movement was prepared to come into the open, but an uprising could interfere with Allied military plans, cause unnecessary casualties and create confusion at the very moment the war was approaching its conclusion. So the Seri Thai waited. They had spent years preparing for the battle that might decide Thailand’s fate, but the battle never came.

Japan Surrenders

In August 1945, Japan surrendered, and for the Seri Thai the moment they had prepared for arrived in a completely unexpected form. There would be no great uprising, no campaign through the mountains and no final assault on Japanese positions. Instead, the men who had been preparing to fight the Japanese emerged from hiding and helped ensure that the defeated Japanese forces handed over their weapons and withdrew.

In the Sakon Nakhon and Phu Phan area, forces associated with Tiang Sirikhan helped supervise the disarmament and withdrawal of Japanese personnel. Several accounts describe Tiang’s forces as taking part in, and in some local accounts leading, the final disarmament in the region. The surviving accounts say that they met with little or no resistance from the Japanese military.

The Japanese were no longer an enemy force that had to be defeated in battle. They were a defeated army that had to be disarmed and removed. After years of preparing for war, the Seri Thai were suddenly helping to bring the occupation to an orderly end. In its own way, that was a remarkable victory.

Eight Thousand Step Into the Light

For almost four years, the Seri Thai had existed largely in secret. Then, on 25 September 1945, Bangkok saw just how large the movement had become. Approximately 8,000 Seri Thai representatives from different parts of Thailand took part in a huge public parade along Ratchadamnoen Klang Avenue, passing the Democracy Monument.

The parade was filmed, and surviving black-and-white footage provides a remarkable record of the occasion. The men and women who had spent years operating secretly were suddenly visible in the heart of Bangkok, many carrying weapons and equipment supplied by the Allies, while crowds gathered along the road to watch.

The parade was not simply a celebration of victory. It was a political statement. Thailand had formally declared war on Britain and the United States during the Japanese alliance, and the Seri Thai now wanted the world to see that an organised Thai resistance movement had existed throughout the occupation and had maintained an armed force with Allied support.

The demonstration had several audiences. It was directed towards the Thai people, the Allied powers and the wider international community. It showed that the weapons supplied to the resistance had not disappeared into private hands, and that Thailand possessed an organised national force independent of Japan. Most importantly, it helped reinforce the argument that Thailand should not be treated simply as a defeated enemy state.

The film also reveals something that is sometimes lost when the parade is described simply as the march of 8,000 armed fighters. The participants represented a much broader movement, while civilians and spectators lined Ratchadamnoen. Students, workers, merchants and others were among those who came to watch.

Afterwards, representatives of the different Seri Thai groups gathered at Thammasat University, where Pridi thanked those who had served. His later account stressed that the movement had acted in service to the nation rather than for political or personal reward. The underground movement had finally stepped into the light, and almost immediately, its wartime role was over.

Remembering Seri Thai

The story did not end in 1945. Today, in eastern Bangkok, there is a place where the name Seri Thai has become part of ordinary city life.

Seri Thai Park is a large public park beside a substantial reservoir in Khlong Kum, Bueng Kum District. The reservoir remains part of Bangkok’s flood-retention system, while the surrounding park has become a pleasant local space with trees, walking and jogging paths, sports facilities, gardens and areas where families come to exercise or relax. It is not the sort of place that immediately looks like a major historical attraction, and that is part of its charm.

Inside the park is the Seri Thai Memorial Building, which houses a library and the Free Thai Museum. The museum occupies the upper part of the building and is not always open, which may explain why visitors can easily see the library but not realise that a museum is above it.

The building itself has a remarkable connection with the movement. It is an exact replica of the government residence at Ban Phra Athit where Pridi lived during the wartime period. The original building was not Pridi’s private property, but it became associated with his clandestine activities and meetings connected with the resistance. Inside the memorial building, the history of the Free Thai movement is preserved among the ordinary surroundings of a Bangkok neighbourhood park.

There is something fitting about that. The Seri Thai spent the war trying to keep Thailand from being swallowed by a foreign power. Its members hid radios, weapons and airfields, crossed borders, transmitted military intelligence, protected Allied agents and prepared for a battle that ultimately never came.

Today, the attractive tree lined reservoir that once served a very practical purpose is surrounded by people walking, jogging, exercising and enjoying a quiet afternoon in the park. The secret world is gone, but the story remains.

Perhaps the most remarkable thing about Seri Thai is that it did not end with a spectacular final battle. The movement spent years preparing for one, but when Japan surrendered, its members helped disarm the Japanese rather than fight them. Then, only weeks later, thousands of them marched openly through Bangkok carrying the weapons that had once been hidden from view.

For years, they had lived in the shadows. On 25 September 1945 they finally stepped into the light.