Japanese invasion of Thailand

• 1. Introduction

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  The Japanese invasion of Thailand started on the 8th of December 1941, less than five hours before Thai forces agreed to a ceasefire. The assault began roughly two hours ahead of Japan's attack on Pearl Harbor. Because the two events fell on opposite sides of the international date line, Thailand's invasion carries the following day's date. The British had already warned Prime Minister Plaek Phibunsongkhram directly: 'There is a possibility of imminent Japanese invasion of your country. If you are attacked, defend yourselves. The preservation of the true independence and sovereignty of Thailand is a British interest, and we shall regard an attack on you as an attack upon ourselves.' Despite that promise, when Japanese troops came ashore, Phibun could not be found.

  Why the prime minister could not be located as Japanese troops came ashore is one question this documentary answers. How a five-hour clash ended in alliance rather than resistance is another.

• 2. Origins Of An Ideology

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  Tanaka Chigaku, active in the mid to late 1800s, framed hakkō ichiu as a principle of divinely ordained expansion. He believed imperial rule was meant to unite the entire world under the Emperor's moral leadership. Japanese nationalists later recast the same phrase to mean freeing Asia from colonizing powers and placing Japan at the top of the region. In 1940, Prime Minister Fumimaro Konoe broadened the idea into the Greater East Asia Co-Prosperity Sphere. It was meant to bind Japan, Manchukuo, China, and parts of Southeast Asia into one bloc. Imperial propaganda called this a benevolent alternative to Western domination, promising shared prosperity to Asian nations free of colonial rule.

  A thirty-man team, Number 82 Section, also known as the Taiwan Army Research Unit or Doro Nawa Unit, formed in 1939 or 1940. Its task was to plan the Strike South campaign. Colonel Yoshihide Hayashi commanded the unit during its final planning stages. That ambition would soon run headlong into a border war Thailand had fought a year earlier, reclaiming territory lost in the Franco-Siamese crisis of 1893.

• 3. Bangkok's Impossible Choice

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  On the 31st of January 1941, Japan stepped in as a negotiator between French Indochina and Thailand, settling their border war. The role gave Japanese officers an opening. In secret discussions around the same time, they asked Prime Minister Plaek Phibunsongkhram for free passage through Thai territory. Phibun answered positively, even though he had signed the British-Thai Non-Aggression Pact on the 12th of June 1940. By February, the British suspected Japan was eyeing bases inside Thailand for a wider assault on Southeast Asia.

  France had already fallen to Germany, Britain was consumed by the war in Europe, and the United States still held to neutrality. Phibun's dilemma deepened as Japan kept building up forces just across the border in Indochina. Midway through 1941, Phibun asked London and Washington for a guarantee of military support if Japan invaded. Neither government could promise it. Winston Churchill favored warning Japan publicly that an invasion of Thailand meant a British declaration of war. But the United States would not agree, and Britain would not act alone.

  By August, the two allies had placed sanctions on Japan instead. In response, Japan offered to ease those sanctions by promising not to encroach on Thailand and by withdrawing troops from Indochina. The offer was conditional: the United States had to stop supporting China. Both London and Washington rejected it, given the toll that would take on China.

  On the 1st of December, Japanese Prime Minister Hideki Tojo said he was still unsure whether Thailand would grant passage, though he hoped to avoid a clash. Talks between the Japanese representative Tamara and Phibun on the 2nd and the 3rd of December narrowed the terms further. Phibun agreed to let Japanese troops through the Kra Peninsula but wanted the Bangkok Plain avoided. In return, he wanted Thailand to regain territory ceded under the Anglo-Siamese Treaty of 1909. He also wanted part of Burma's Shan State. That same day, the 2nd of December, Tokyo issued the coded order Climb Mount Niitaka, setting the wider Pacific war into motion. Two days later, the main invasion fleet slipped out of Sanya on Hainan Island, gathering more ships from Cam Ranh Bay in Indochina as it steamed south.

• 4. First Shots Over The Gulf

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  At noon on the 6th of December, a Lockheed Hudson from the RAAF's No. 1 Squadron spotted three Japanese ships steaming west. The sighting took place over the South China Sea. About 15 minutes later, it sighted the full convoy: a battleship, five cruisers, seven destroyers, and 22 transports of the IJN Southern Expeditionary Fleet. The seaplane tender Kamikawa Maru launched a Mitsubishi F1M Pete floatplane to intercept, but the Hudson escaped into the clouds. Minutes afterward, a second Hudson also sighted the convoy. Air Chief Marshal Sir Robert Brooke-Popham learned of the sightings at 14:00 but could not act, since Britain and Japan were not yet at war. He placed his forces in Malaya on full alert and ordered continued surveillance.

  At 03:00 on the 7th of December, Vice-Admiral Jisaburō Ozawa ordered patrols between the convoy and Malaya, then about 100 nautical miles from Kota Bharu. Heavy rain and zero visibility greeted the seaplane tenders Kamikawa Maru and Sagara Maru as they launched 11 F1M2 and six Aichi E13A floatplanes. About 20 nautical miles northwest of Panjang Island, at 08:20, an E13A1 floatplane coded ZI-26 spotted an RAF Consolidated PBY Catalina flying boat. Ensign Ogata Eiichi was piloting the floatplane; Warrant Officer William E Webb commanded the Catalina, numbered W8417. Ogata attacked from the rear, damaging the Catalina and destroying its radio, then shadowed it for 25 minutes. Five Nakajima Ki-27 Nate fighters from the JAAF's 1st Sentai in Indochina arrived and shot the flying boat down. Webb and his crew became the first casualties of the Pacific War. The British, unaware of the incident, took no action. Ogata himself would later be killed in the Battle of the Coral Sea.

  At 23:00 that same night, Japan presented the Thai government with an ultimatum demanding passage for its military. The Thais were given two hours to answer.

• 5. Forces On Both Sides

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  Thailand fielded a well-trained army of 26,500 men, a number that reserves pushed close to 50,000 once mobilized. The Royal Thai Air Force operated some 270 aircraft, 150 of them combat types, many built in the United States. Japan itself had supplied Thailand with 93 more modern aircraft in December 1940. The Royal Thai Navy, by contrast, was poorly trained and equipped, having lost a substantial number of vessels fighting French Indochina. Two submarines still ran, HTMS Matchanu and HTMS Wirun, and their presence worried Japanese commanders enough to note it. Along the Kra Peninsula, Thailand organized new units at each threatened point. The 38th Infantry Battalion took up position near Chumphon. The 39th Infantry Battalion and 15th Artillery Battalion gathered around Nakhon Si Thammarat. The 40th Infantry Battalion held Trang, the 41st Infantry and 13th Artillery Battalions held Songkla, and the 42nd Infantry Battalion held Pattani. The 5th Infantry Battalion had been the first to move south, transferred to Hat Yai by military train on the 18th of February 1940.

  Facing them, Japan had massed roughly 100,000 troops who needed passage through Thailand. Lieutenant General Shōjirō Iida commanded the 15th Army, tasked with the route into Burma across the Bangkok plain. Lieutenant General Tomoyuki Yamashita commanded the 25th Army, aimed at Malaya and Singapore through the Kra Peninsula. Colonel Masanobu Tsuji, a member of Unit 82, had drawn up the plan for the push through Thailand. At sea, Admiral Nobutake Kondō's IJN 2nd Fleet covered the landings in Thailand and at Kota Baru in Malaya. The cruiser Kashii escorted seven transports carrying troops of the 143rd Regiment from Saigon. Destroyers Asagiri, Amagiri, Sagiri, and Yugiri screened the 25th Army's landings in southern Thailand. In all, 18 transports took part, three of them bound for Kota Baru.

  Within hours these forces would meet not at a single front, but at half a dozen scattered points along Thailand's coast.

• 6. Landings Across The Coast

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  At dawn on the 8th of December, the Imperial Guards Division under Lieutenant General Takuma Nishimura crossed from Indochina into Thailand's Phra Tabong Province. The IJA 55th Division under Lieutenant General Hiroshi Takeuchi crossed alongside them, entering at Tambon Savay Donkeo in Battambang's Athuek Thewadej District. They met no resistance. From Sisophon they swung northwest into Aranyaprathet, following a railway link to Monkhol Bourei that was still under construction; it would not open until the 11th of April 1942.

  At Chumphon, the Japanese 1st Infantry Battalion of the 143rd Infantry Regiment landed from two troopships on the morning of the 8th of December. They formed a perimeter, but Thai defenders pinned them down. The 52nd Yuwachon Thahan Training Unit, youth cadets from Sriyaphai Secondary School, fought alongside the regular 38th Infantry Battalion and the provincial police. Fighting ended that afternoon when the Thais received a ceasefire order. Thailand lost Captain Thawin Niyomsen, commander of the 52nd Yuwachon Thahan Unit, posthumously promoted to Lieutenant Colonel. Several provincial policemen and a few civilians also died.

  Nakhon Si Thammarat hosted the Sixth Army Region's headquarters, along with the 39th Infantry Battalion and 15th Artillery Battalion. Three Japanese troopships, the Zenyo, Miike, and Toho Maru, anchored offshore during the night of the 7th of December, escorted by the Shimushu. They carried 1,510 men and 50 trucks. Aboard were the 3rd Infantry Battalion of the 143rd Regiment and the 18th Air District Regiment, along with an army signals unit. Also aboard were the 32nd Anti-Aircraft Battalion and the 6th Labour Construction Company. Troops began disembarking shortly after midnight at Tha Phae canal, north of the main Thai army base, Camp Vajiravudh. The Thais, already alerted by the landing at Songkhla, went into action immediately. Fighting lasted until midday, when the prime minister's ceasefire order arrived.

  Prachuap Khiri Khan housed the Royal Thai Air Force's Fifth Wing, commanded by Wing Commander Mom Luang Prawat Chumsai. The Japanese 2nd Infantry Battalion of the 143rd Regiment, under Major Kisoyoshi Utsunomiya, landed at 03:00 from a single troopship. They crushed local police resistance and took the town. Further landings hit the airfield to the south, where Thai airmen and provincial police held out until noon the next day. Japanese estimates put their own losses at 115 dead; Thai estimates put Japanese losses at 217 dead and over 300 wounded. Thailand lost 37 dead and 27 wounded.

  At Samut Prakan, the Japanese 3rd Battalion of the 4th Guards Infantry Regiment landed in the early hours of the 8th of December. Their objective was Bangkok. A small Thai police detachment met them. The standoff stayed tense but bloodless, and the Japanese agreed to hold off entering the capital until formal negotiations concluded.

  In Bangkok itself, a single Japanese bomb struck the main post office and failed to explode. Police rounded up Japanese residents while the cabinet debated its options and waited for Phibun to appear. Some ministers favored continued resistance, even a government in exile. When Phibun finally arrived, the cabinet chose to give way. Japanese troops then occupied the Chinatown district of Sampeng and turned the Chamber of Commerce Building into a command post.

  At Don Muang Royal Thai Air Force Base, defending Thai pilots faced a numerically superior Japanese air force and lost six fighter planes.

  At the coastal village of Ban Don, a Japanese infantry company from the 1st Battalion of the 143rd Regiment landed from one troopship. It came ashore in the early hours of the 8th of December. They marched inland to Surat Thani, where Royal Thai Police and civilian volunteers met them amid a rainstorm. Fighting only ended in the afternoon, once exhausted Thai defenders were ordered to lay down their arms. Thailand lost 17 or 18 dead; the number of wounded was never recorded.

  Pattani ranked as the 25th Army's second most important objective, close as it was to the Malayan border. Eight IJN destroyers, including the Shirakumo and Shinonome, escorted five troop transports carrying the 42nd Infantry Regiment of the IJA 5th Division. Major Shigeharu Asaeda commanded the landing force. Rough seas and unsuitable landing grounds slowed them down further. Thai defenders resisted until ordered to cease fire at midday. They included the 42nd Infantry Battalion, Pattani's Provincial Police, and the 66th Yuwachon Thahan Training Unit from Benjama Rachoothit School. The Thai battalion commander, Khun Inkhayutboriharn, died in the fighting along with 23 other ranks, five Provincial Police, four Yuwachon Thahan cadets, and nine civilians. Asaeda had gathered intelligence across Burma, Thailand, and Malaya before the war began, as a member of Taiwan Army Unit 82. He had picked Pattani as the landing site himself. He chose a beach that looked sandy but hid a muddy seabed beneath it. That hidden mud slowed his own men during the landing.

  Songkhla, also called Singora, stood as the main objective of Yamashita's 25th Army. In the early hours of the 8th of December, three regiments of the Japanese 5th Division landed from ten troop transports at Songkhla. Colonel Tsuji led them, serving under Lieutenant General Matsui Takuro. The Thai garrison at Khao Khor Hong, the 41st Infantry Battalion and 13th Artillery Battalion, took up positions along the roads to Malaya. They were brushed aside by the main Japanese advance. A further clash flared at Hat Yai. Thailand lost 15 dead, eight from the 41st Battalion and seven from the 5th, and between 30 and 55 wounded. Fighting stopped at noon once armistice orders came through.

  Further south, troops of the 25th Army landed simultaneously at Kota Bharu in Malaya. Once Thailand was secured, the 143rd Regiment moved north to relieve the Imperial Guards. The Guards turned south to join the push into Malaya and Singapore. The 15th Army, meanwhile, pressed on toward Burma.

  Within hours, the ceasefire would let Japanese squadrons put that captured Songkhla airfield to a very different use.

• 7. A Reluctant Alliance

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  Within hours of the ceasefire, Japanese squadrons had already flown into the captured airfield at Songkhla from Indochina. From there they could launch air raids on Malaya and Singapore at close range. Phibun's decision to sign the armistice ended any hope Churchill held of pulling Thailand into a British alliance. It also gave Japan a base from which to invade Malaya next door. On the 14th of December, Phibun signed a secret agreement committing Thai troops to fight alongside Japan in the Malayan and Burma campaigns. A formal alliance between Thailand and Japan followed on the 21st of December 1941. By the 25th of January 1942, the Thai government had declared war on both the United States and the United Kingdom. Washington responded by freezing all Thai assets held in the country. In London, the Thai ambassador delivered the declaration of war as instructed. In Washington, Thailand's ambassador Seni Pramoj refused to do the same, and instead organized the Free Thai Movement.