The Royal Thai Air Force was a part of the United States military during World War II. In return for their support, the Americans gave them fighter planes and trained pilots.

The Royal Thai Air Force Official Website is a website that tells the story of how the Royal Thai Air Force both fought and supported America during World War II. Read more in detail here: royal thai air force official website.

The RTF was a dual-purpose service that flew for the Japanese while simultaneously fighting against them as an OSS covert collaborator.

“I didn’t even realize we were at war with Thailand,” a young American P-38 pilot from the 449th Fighter Squadron wrote to his parents after a brutal and deadly combat with five Nakajima Ki-27b Royal Thai Air Force aircraft in November 1944. I didn’t even know what Thailand was called; I assumed it was Siam.”

It’s natural that he’s perplexed. Siam had changed its name to Thailand in July 1939 and declared war on the United States soon after the assault on Pearl Harbor. However, there is still debate regarding Thailand’s involvement in World War II. Many military history enthusiasts are unaware that Thailand allied with Japan and that Thailand was the target of many bombing attacks by the US Army Air Forces, including the first B-29 combat mission.

The odd tale of the Thai–Japanese alliance during WWII is much more complex than most historical sources, which reduce aerial combat between Royal Thai Air Force pilots and their U.S. Army Air Forces opponents to footnotes or a few cryptic lines strewn among hundreds of sources. Those air battles, however, are just as fascinating and dramatic as any other in the China-Burma-India (CBI) Theater, and they provide an important dimension to the conventional CBI narrative. They’re even more extraordinary since the Royal Thai Air Force had a double life, flying for the Japanese while simultaneously assisting in the war against Japan as a covert collaborator of the CIA’s predecessor, the Office of Special Services (OSS). 

By November 1941, the Thai government was convinced that war between Japan and the United States was on the horizon. Thailand, as the customary buffer state between British Burma to the west and French Indochina to the east, did what it did best: it accommodated. That meant supporting the region’s strongest power, which most Thais saw as Japan. Despite this, the Royal Thai Air Force (RTAF) sympathized more with the Americans than the Japanese due to training and connection. This was partly due to the fact that the US provided nearly all of the RTAF’s combat aircraft throughout the 1930s. For the most of the 1930s, the finest and brightest RTAF commanders were also educated in the United States at the Air Corps Tactical School at Maxwell Field, Alabama. They formed enduring bonds with their American counterparts there, and American techniques were integrated into the RTAF combat philosophy.

Why the Royal Thai Air Force Both Fought and Supported America During World War II As the war progressed, Thailand’s prime minister, Phibun Songkhram, was pro-Japanese and eager to support Japan. (PL/Alamy Archive)

As a result, senior air force commanders did not share Thailand’s prime minister, Field Marshal Phibun Songkhram, or major sectors of the Thai Army’s pro-Japanese attitude. When the Japanese mediated the short conflict between Thailand and Vichy France in 1940, Phibun, a fascist admirer, became a supporter of Japan. Phibun became passionately pro-Japanese in exchange for Japan successfully pressing France to restore Indochina border areas to Thailand; he had plainly chosen sides. The Royal Air Force, on the other hand, was prepared to combat Japanese troops if they invaded. 

They didn’t have to wait long. The Imperial Japanese Army started landing troops along the Kra Isthmus, a small strip of land south of Bangkok, at 3 a.m. on December 8, 1941 (December 7, Pearl Harbor time). Wing 5 of the RTAF, stationed on the isthmus, prepared to assault the approaching forces in retaliation. They were immediately taken aback: Pilot Officer Maen Prasongdi took off first in a Curtiss Hawk III biplane fighter and tried to target troopships in the eastern port before being shot down by Japanese antiaircraft fire. Another aircraft, flown by Flight Sergeant Phrom Shuwong, had hardly taken off when it was forced to crash-land on the runway due to groundfire. Japanese troops shot and killed Phrom as he got out of his aircraft. Two additional RTAF pilots were killed while attempting to take to the air. When Japanese soldiers and tanks approached the airport, the wing commander ordered his men to destroy the airfield’s structures and retreat into the jungle to continue the battle. 

Why the Royal Thai Air Force Both Fought and Supported America During World War II On December 8, 1941, Japanese invaders make their way into Bangkok, having encountered minimal opposition on the ground. Thailand surrendered within hours, subsequently declaring war on the United States and the United Kingdom. (

The Japanese Imperial Guards Division stormed into Thailand against minimal opposition at the Thai–Cambodia border east of Bangkok. With 11 Nakajima Ki-27 fighters—dubbed “Nate” by the Allies—and nine Mitsubishi Ki-30 (or “Ann”) light bombers flying above, the Japanese Army’s 10th Air Brigade supported the assault. Three pilots from the RTAF’s 43 Squadron got into their Hawk IIIs to attack the Japanese aircraft above at about 6 a.m. The more competent Nates—fighters with exceptional turning ability—quickly shot down all three Hawk IIIs, killing the pilots in the ensuing battle.      

Field Marshal Phibun convened his cabinet shortly after 7 a.m. They soon realized that continuing to fight was useless, and the Thai government declared a ceasefire a half hour later. Thailand surrendered because it had no other choice. Wing 5 defenders were enraged and kept fighting until noon the next day, despite the ceasefire order. The battalion lost 38 soldiers killed and 27 wounded, while the Japanese suffered 115 casualties.

“The tree that bends with the wind is the tree that endures the storm,” according to an ancient Thai adage. The die was cast when Japanese soldiers arrived in Bangkok late that afternoon. Thailand bowed to the winds of war in the face of an invasion, overt threats of war, and Phibun’s pro-Japanese attitude. On December 21, 1941, the prime minister signed a Pact of Alliance with Japan and expelled from his cabinet all those who opposed the alliance. Phibun took the unusual step of declaring war on the United Kingdom and the United States a month later, after British Royal Air Force Buffalo aircraft strafed Japanese-occupied airfields close inside the Thai border. 

The RTAF faced a difficult decision as a result of that statement and the agreement with Japan. Most air force commanders had little inclination to collaborate with Japan after losing planes and pilots in combat against the Japanese. “You don’t have to like the Japanese, but as professionals, we must follow out Phibun’s orders,” the RTAF commander, Air Vice Marshal Atueg Tevadej, eventually said to his troops.

Why the Royal Thai Air Force Both Fought and Supported America During World War II Throughout the 1930s, the United States provided the Royal Thai Air Force (RTAF) with aircraft, including the types seen above, as well as training for some of its commanders, fostering a feeling of affinity with the US among the RTAF (Marcelo Ribeiro)

Why the Royal Thai Air Force Both Fought and Supported America During World War II H-75N (P-36) Curtiss Hawk (Marcelo Ribeiro)

Why the Royal Thai Air Force Both Fought and Supported America During World War II 139W (B-10) Martin (Marcelo Ribeiro)



RAF bombers stationed in Burma sparred with Royal Thai Air Force fighters near the Thai border during the early months of 1942. Air assaults progressively faded when the Japanese 15th Army began the major overland invasion of Burma from Thailand on January 22, as the Japanese advance pushed British planes out of range. As a consequence, the RTAF moved the majority of its operations to northwest Thailand to fulfill a new mission for Japan: pushing Chinese forces out of the eastern Shan States, a harsh, mountainous region bordering Burma, Thailand, Laos, and a tiny section of China. 

The Thai Army advanced into the Shan States on May 10, 1942. The pattern of RTAF operations remained consistent for the next nine months: Vought V-93 Corsairs and Curtiss Hawk IIIs flew the majority of close-support missions, while Ki-30 light bombers, Ki-21 medium bombers, and export versions of the Martin B-10 bomber flew longer-range missions to strike Chinese troop concentrations in larger towns. Although there was no air-to-air combat over the Shan States, RTAF pilots had to deal with a lot of ground fire and flak from Generalissimo Chiang Kai-forces. Shek’s

The late-January 1943 bombing raids were usual. To alleviate the strain on Thai Army troops, 17 Ki-30s from two RTAF squadrons attacked enemy positions on January 24. On the 29th, a mixed formation of 19 Ki-30s and Ki-21s equipped with incendiary bombs assaulted the Chinese stronghold at Mong Sae on the Burma-China border, setting houses ablaze and damaging a major weapons store. The attacks were tactically and strategically successful, and Chinese soldiers retreated over the border into Yunnan Province a few days later. 

The Royal Thai Air Force updated its inventory with new equipment from January 1942 until December 1943. Thailand got a dozen upgraded Ki-27b Nate fighters and 24 Nakajima Ki-43 “Oscar” fighters as Japan’s sole ally in the area. The Oscar was light, simple to fly, and praised for its combat prowess, similar to the Mitsubishi A6M Zero in both appearance and performance. Although it could outmaneuver most aircraft, the Oscar lacked armor and self-sealing fuel tanks, making it infamous for collapsing or setting fire after receiving minor damage. 

Why the Royal Thai Air Force Both Fought and Supported America During World War II Following Thailand’s alliance with Japan, the Japanese supplied the Thais with modern combat aircraft, including these two Nakajima fighters. The Nakajima Ki-27 “Nate” is seen above (Marcelo Ribeiro)

Why the Royal Thai Air Force Both Fought and Supported America During World War II Oscar Nakajima Ki-43 (Marcelo Ribeiro)


With the addition of two new bomb groups and three new fighter groups to the US Army Air Forces in the CBI Theater in 1943, strategically vital Bangkok rose to the top of the target list. Against the evening of December 19, 1943, a group of 27 B-24 Liberator heavy bombers attacked the city’s ports, marking the start of the new bombing assault on the Thai capital. Thai counter-offensive consisted of searchlights and anti-aircraft fire. On December 23, a few nights later, 26 Liberators attacked Bangkok’s major train station. During this operation, American bombers saw two German aircraft in the air, but none of them attacked. The RTAF was unprepared and unsuccessful on these early operations. RTAF fighters didn’t scramble until the bombers were almost above since they didn’t have radar or an early warning system. The bombers had already left by the time they gained altitude and looked around in the darkness.  

The United States Fourteenth Air Force, led by Major General Claire Chennault, the famous commander of the Flying Tigers, launched attacks on targets in northwest Thailand, concentrating on headquarters complexes and communication hubs near Chiang Mai and Lampang. On December 31, 1943, a formation of 25 B-24 bombers attacked the railroad marshalling yards at Lampang in an unaccompanied daylight strike. Six Ki-27 Nates from the RTAF’s 16 Squadron attempted to intercept the B-24s, however the American aircrew claimed that the Thai fighters first held back from striking then jinked away as the Fourteenth Air Force heavy bombers opened fire. Two P-38 Lightnings from the 449th Fighter Squadron escorted 28 B-24 Liberators on a second flight to Lampang three days later. Thai fighters scrambled once again but did not assault. The RTAF’s apparent lack of aggression came from a lack of knowledge rather than a lack of nerve. They couldn’t accomplish much even in broad daylight because to insufficient forewarning caused by a lack of ground radar guidance. 

On March 5, 1944, Fourteenth Air Force B-25 medium bombers began the interdiction campaign because 400 miles of roads and rail links connected Bangkok and Chiang Mai. The B-25s’ primary objectives for the rest of the spring were those critical highways and rail bridges. Thai pilots were irritated and seldom intercepted the Americans. A Hawk 75N pilot scrambled and launched an assault on B-25 bombers bombing the Ban Dara bridge south of Lampang on one occasion. The RTAF pilot only made one firing pass, according to Thai records, since his fighter was too sluggish to catch up with the bombers. The Thais resorted to overlapping daytime combat patrols to counter B-25 attacks, but none of them were effective. The only time there was a break from bombing assaults was during the summer, when monsoon rains slowed Allied operations.  

Why the Royal Thai Air Force Both Fought and Supported America During World War II An “Oscar” fighter pilot compares notes with a Thai and Japanese pilot (above); the RTAF adopted the elephant emblem in late 1942. The United States Fourteenth Air Force, located in China and led by Major General Claire Chennault, was one of their adversaries (below). (

Why the Royal Thai Air Force Both Fought and Supported America During World War II (Getty Images/Harry Warnecke/NY Daily News Archive)

DURING THE FIRST HALF OF 1944, two significant military operations placed Thailand in the sights of the United States Army Air Forces’ newest and most technologically sophisticated strategic bombers. Lieutenant General Renya Mutaguchi, commander of the Japanese 15th Army, began “Operation U-Go,” the invasion of India, in early March. Because most of his operation’s logistical assistance came from Thailand, the Allied air assault against Thai targets grew in intensity. 

Thailand was also an unexpected participant in the Allies’ “Operation Matterhorn.” The strategic plan for this operation, which was authorized at the Quebec and Cairo Conferences in 1943, called for stationing squadrons of new long-range Boeing B-29 Superfortress heavy bombers in India and China to conduct strategic attacks on mainland Japan. 

Brigadier General Laverne G. Saunders, ironically called “Blondie” because to his jet-black hair, took command of the newly created 58th Bomb Wing in Kharagpur, India, at a hurriedly built base for the first operational B-29 unit. The commander faced a number of challenges, including an untested and unpredictable brand-new aircraft, inexperienced aircrews, and a logistical system that couldn’t provide enough fuel or replacement components. To iron out the wrinkles, the 58th Bomb Wing’s B-29s were given their first combat mission: an assault on Bangkok’s train yards on June 5, 1944.

Why the Royal Thai Air Force Both Fought and Supported America During World War II In June 1944, a new B-29 takes off from an even newer runway in India. That month, the first-ever B-29 mission bombed railroad yards in Bangkok, resulting in the loss of six B-29s. (From the National Archives)

On the operation, 98 B-29s took off; one crashed on takeoff, killing the whole crew, while at least 20 others were forced to abort due to technical issues. Heavy cloud cover concealed the train yards, requiring half of the aircraft to bomb via radar. The first B-29 to fire a shot in anger was above the objective at 10:52 a.m. Because few crews had undergone radar bombing training, they were forced to rely on “on-the-job training.”

During the operation, nine RTAF Oscars attempted but failed to intercept the stream of bombers. The B-29s’ return flight proved to be much more dangerous. Two B-29s crash-landed, and two more ditched in the Bay of Bengal after running out of fuel. Despite the loss of 15 personnel, two B-29s, and a total of six B-29s, XX Bomber Command declared its first combat operation a success. It conveniently ignored the fact that visual reconnaissance revealed that just 18 bombs were dropped near the designated target. “The damage would create no significant reduction in the movement of soldiers and military supplies into Burma,” according to the tactical mission report. 

The operation on November 2, 1944, was the only one where RTAF pilots drew blood during the Operation Matterhorn B-29 attacks on Bangkok. 55 B-29s bombed the railroad marshalling yards on the outskirts of Bangkok during this daytime assault. The Thais scrambled seven Oscars in their opposition. Flight Lieutenant Thorsak Worrasap, piloting an Oscar, opened fire on a B-29 aircraft, burning it on flames. He tried to pursue his target, but his aircraft was damaged by return fire from the other bombers, causing him to bail out. 

Nine days later, above Lampang in northwest Thailand, one of the biggest recorded fights between RTAF and US Army Air Forces fighters occurred. Nine P-51C Mustangs from the 25th Fighter Squadron and eight P-38 Lightnings from the 449th Fighter Squadron conducted an armed reconnaissance mission into the region on November 11, 1944. Before going on to a neighboring airport, the American aircraft strafed and destroyed a train during their first assault. Five RTAF Ki-27b Nates from 16 Squadron were able to scramble during the short delay.

Why the Royal Thai Air Force Both Fought and Supported America During World War II Bombs from the United States hit Lampang Airfield. The airfield’s buildings and runway had been “neatly identified,” according to the photo’s wartime caption. (From the National Archives)

The Nates arrived at their patrolling height just as American jets strafed Lampang Airfield, killing one of the runway’s planes. The top-cover P-38s rolled into action as the RTAF pilots maneuvered to attack, each spewing 20mm rounds from a single cannon and torrents of fire from four.50-caliber machine guns. The five Nates were divided into two groups right once, with Flying Officer Kamrop Bleangkam and Chief Warrant Officer Chuladit Detkanchorn pursuing the P-38s and the other three Nate pilots attempting to repel the Mustangs. The agile Nates outmaneuvered their opponents for the most part during the furball battle that followed, but the Thai pilots were severely outnumbered and outgunned and had little chance in the lopsided encounter. Before another Lightning jumped him and forced him to crash-land, Kamrop grabbed onto one P-38 and claimed to have shot it down with its right wing in flames. Chuladit was shot down by yet another P-38.   

The Nate, with just two 7.7mm machine guns compared to the P-51C’s four.50-caliber machine guns, didn’t have much offensive punch, but some RTAF pilots put their weaponry to good use against the Mustangs. “I see two below and am coming after them,” Second Lieutenant Henry Minco yelled as four P-51s ascended to join the P-38s fighting Kamrop and Chuladit. Lieutenant Minco, on his 71st combat mission, was never seen again after diving into the whirling battle. Many months later, word came in via Thai connections that Minco had died. They further said that the American pilot was buried by missionaries.  

RTAF Flight Lieutenant Chalermkiat Vatthanangkun flew into a wall of.50-caliber tracers as the battle continued above Lampang, his Nate sustaining several blows to its engine. After a forced landing, one of the Mustangs strafed and destroyed Chalermkiat’s fighter. P-51s killed the two surviving Nates as the unequal fight ended: Chief Warrant Officer Thara Kaimuk was shot down and crashed nine miles from Lampang, and Chief Warrant Officer Nat Sunthorn perished when his Nate crashed. 

WHILE THESE AIR CAMPAIGNS WERE IN FULL SWING, AN UNDERGROUND RESISTANCE MOVEMENT HAD BEEN FORMING SINCE THE BEGINNING OF THE WAR. After Thailand declared war on the United States in 1942, the Free Thai Movement (or Seri Thai) arose. Seni Pramoj, Thailand’s ambassador in Washington, D.C., declined to provide Secretary of State Cordell Hull with the declaration of war, instead proposing that he “assemble and maintain a government of genuine patriotic, liberty-loving Thais while my government is in the clutches of Japan.” Washington made the correct decision to treat Thailand as an occupied rather than hostile country. Ambassador Seni, a conservative nobleman with a long history of anti-Japanese sentiment, launched the campaign with American help.

Why the Royal Thai Air Force Both Fought and Supported America During World War II Seni Pramoj, Thailand’s ambassador in Washington, D.C., declined to deliver the declaration of war against the United States, instead organizing a guerilla group known as “Free Thai” to resist the Japanese. (Courtesy of the Library of Congress)

Then there’s the OSS. Seni proposed infiltrating a group of Thai students in the United States into their country for subversive activities on March 12, 1942. Seni’s team then met with Lieutenant Colonel Garland H. Williams of the OSS to plan the training, equipping, and deployment of the young volunteers. On June 12, 1942, the first batch of 13 Thais started OSS training. Many of the young Thais who had been educated at different OSS facilities in Maryland and Virginia in 1942 were parachuted into Thailand in 1944 and 1945 for espionage operations, guerilla network organization, and information gathering. They also assisted in the recovery of fallen Allied pilots. 

Lieutenant William D. McGarry, a Flying Tigers P-40 pilot with eight wins, was one of the most spectacular rescues. McGarry was shot down by antiaircraft fire over Chiang Mai on March 24, 1942, arrested, and imprisoned at Thammasat University in Bangkok, where he was guarded by Thai, not Japanese, troops. Unbeknownst to the Japanese, he was also being watched over by Pridi Phanomyong, the university’s rector and a prominent figure in the Free Thai movement. Pridi informed the Japanese that McGarry had died in captivity after connecting with an OSS-trained Thai national who had been parachuted in on September 9, 1944, to assist him. The pilot was then smuggled out of the prison camp in an improvised coffin and hidden in a Thai customs boat with four Royal Thai Air Force officers. McGarry’s escape boosted the RTAF’s double existence and helped the US deepen its relationship with a hesitant foe.

Why the Royal Thai Air Force Both Fought and Supported America During World War II Downed American pilot William D. McGarry (top) was smuggled out of prison with the assistance of free Thai agents; his damaged P-40 (bottom) is currently on exhibit at the RTAF museum. (The Association of Flying Tigers)

Why the Royal Thai Air Force Both Fought and Supported America During World War II (Photo courtesy of the Royal Thai Air Force Museum)

The connection between the RTAF and the Free Thai Movement had been developing since Group Captain Tevarit Panleuk took over as the new RTAF commander in April 1943. He was much more friendly to the movement than the previous commander, and enabled Free Thai to utilize air force facilities and equipment for their clandestine operations. He was secretly pro-American and a graduate of the Air Corps Tactical School.

When American OSS operatives started parachuting into Thailand in mid-1944, the RTAF volunteered its planes to carry them wherever they were required, thereby creating a covert airline. Because of the effectiveness of the subterranean airlift, RTAF planes started flying agents straight into Bangkok’s Don Muang Airfield, which it shared with the Japanese.

The difficult job of supplying food and weaponry to the burgeoning Thai underground was made simpler for the Allies by having access to secret airfields established by the RTAF in 1944–45. The supplies could subsequently be distributed across the nation by RTAF planes, directly under the noses of Japanese troops. The RTAF also supplied meteorological information, real-time Japanese army movements, and possible targets for American fighter/bomber attacks to the Allies. In one instance, an RTAF officer flew with American bombers on multiple sorties against Thailand to verify that targets were correctly selected.

The RTAF found itself in an ethical quandary as a result of continued American air assaults on targets in Thailand. The RTAF was forced to watch as its own troops and equipment were assaulted alongside the Japanese after providing most of the information on Japanese air strength. For example, on April 9, 1945, roving Tenth Air Force Mustangs strafed the joint Thai–Japanese airfield at Lopburi, some 80 miles north of Bangkok, killing 15 RTAF aircraft. As a consequence, they were torn between two worlds: how to protect targets while providing critical information to an adversary bombing them? 

The advent of the monsoon in May 1945 offered a solution rather than a response, since the rain significantly reduced the bombing campaign against Thailand. Attacks on Thai airfields, as well as confrontations between RTAF and Allied aircraft, stopped for all practical purposes. The RTAF thereafter dedicated the majority of its sorties to assisting the Free Thai Movement until the conclusion of the conflict. 

The Royal Thai Air Force’s double existence came to an end with Japan’s capitulation. The RTAF had no desire to go to war with the US. Nonetheless, political circumstances had forced it into a corner, and it had done its duty to king and nation as a reluctant friend of the Japanese and an even more reluctant adversary of the US. How did they manage it? “The Japanese increasingly saw Thailand as a conquered region rather than an ally,” a Free Thai Movement member said. The Japanese could never imagine that the pleasant Thai among whom they lived could be capable of such sophisticated subversion because of their sentiments of superiority and attitudes toward the Thai.” The RTAF played a major role in this subversion by fighting and assisting the same adversary at the same time throughout the conflict. Throughout its dual existence, the RTAF shown the bravery and determination to fight behind the scenes for a noble cause much greater than any partnership with Japan: the liberation of Thailand.

Why the Royal Thai Air Force Both Fought and Supported America During World War II “The Americans are your friends,” reads a wartime flyer issued in Thailand. (Image courtesy of HistoryNet Archives)

This story appeared in World War II’s August 2023 edition.

Frequently Asked Questions

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Who had the most powerful air force in ww2?

The United States of America had the most powerful air force in ww2.

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The Allies gained air superiority by using new technology to detect German aircraft and destroy them.

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