Franco-Thai War: The Indochina Micro Campaign, 1940-1941

Thailand's colonial "small war" with France, fought from October 1940 to January 1941, is one of the most unique micro conflicts in the greater military history of World War Two (1939-1945). Despite it's brevity, the Franco-Thai War, is notable for both the significant air campaign which took place over the skies of Laos and Cambodia and the wars' penultimate naval battle at the reefs of Koh Chang, January 1941.

RTAF Curtiss Hawks versus a French Morane-Saulnier during 1940-1941 Franco-Thai conflict

(Artist Depiction)

Following the fall of Paris in June 1940, many thousands of miles away in French Indochina, where French rule had been established in 1862 as French Cochinchina (Vietnam), an entirely different war was brewing. Long angered over border concessions made at the point of a bayonet, Thailand (formerly Siam before 1938), declared war on France's colonial possessions in Laos and Cambodia. No stranger to conflict in Southeast Asia, French soldiers had fought in northern Vietnam during the Tonkin campaigns of 1883-1886 against Chinese imperial armies and Vietnamese rebel groups. 

After the brief Franco-Siam War of 1893, France gained Laos as a territory of French Indochina and some Siamese provinces as well, including Trat, which was seized by force and not returned to Thailand until March of 1906. Thailand had become a nominal power-player in Southeast Asia beginning in the mid-1930s, building a modern military and later allying themselves with the Japanese Empire. In 1938, Colonel Pibul Songgram (Phibun, b.1897-1964) became Prime Minister. His long reign began by quickly agitating against French interests in the region although even Phibun had studied at a military school in France during his collegiate years. 

There was some complexity to the issue of war with France because Thailand had heavy economic ties with England who controlled most of the Thai's money. The Siamese had long depended on the foreign purchase of rice, rubber, and tin which could be halted if the Europeans stopped importing them. The French colonial regime in Indochina had little direction from whatever authority was left on mainland France, acting nearly independent from any central authority. Ultimately, it was the Japanese who proved to be the masters of the region. 

In late September 1940, Japanese Army units attacked a French outpost at Long-San and forced its capitulation. Then northern Vietnam was attacked by a Japanese amphibious force supported by an aircraft carrier. Haiphong in northeastern Vietnam was bombed and for several nights it seemed that Hanoi was even threatened by the might of the Japanese military. This heated "incident" only lasted four days but left 800 French casualties. Both sides eventually backed down though the Japanese had proved the Vichy French colonials had little meaningful resistance to offer.

Border Battle: Thai-Cambodia-Laos Ground Campaign 5-19 January

Skirmishing began in late October and early November in the disputed border regions of Laos and Cambodia. Thai artillery strikes hit French positions early and often, softening their already light border defenses. Bombing raids and some aerial "dogfights" were witnessed in November and carried on into December 1940, precluding the Thai ground offensive in Laos and then Cambodia. The air war is described in the section, Aerial Combat of the Franco-Thai Conflict, below.

The Thai ground offensive began on 5 January 1941 with a large combined air and ground assault against French colonial positions in both Laos and Cambodia. Static fighting erupted on the Laotian border regions of the Dângrêk mountains where neither side could claim victory, although the Royal Thai Army quickly took the northern Laos sector. Thai forces outnumbered the Vichy forces considerably and fielded mechanized units, including Vickers 6-Ton tanks and Carden Lloyd tankettes, whilst the French had no mechanized armor at the front. The colonial French military commanded around 32-38,000 soldiers in Southeastern Asia, of which less than 12,000 were actual French or European soldiers. The majority of French troops would have been Cambodian, Chinese, Vietnamese, or colonial troops from other French colonies.

The most intense combat of the conflict occurred along Colonial Route 1 (RC1), Battambang Province, Cambodia. This general area was where the French counter-attack came at Yang Dam Koum, which was held by Thai forces in Cambodia. Fighting began when a French Cambodian Tirailleurs regiment repulsed the first Thai infantry assault. Colonel Henri Jacomy organized the the French attack against the main Thai force which eventually ended in a total strategic failure. It was the 5th Legionnaire regiment who likely saved the colonial French army from a complete route at Phum Préau on 16 January. Using two 25mm cannons and one 75mm 'flak' artillery gun, the 3rd Battalion, 5e REI Legionnaires battled for eight hours against a heavily armored foe. Three Thai tanks were destroyed in the fighting at Phum Préau, briefly halting the Siamese advance in the province. The legionnaires of the 3rd REI suffered greatly for their heroics, both of their commanding officers were killed and thirty-three legionnaires were wounded or KIA.

A diversionary attack launched by the Brigade d’Annam-Laos on some of the small islands of the Mekong River during the Thai offensive succeeded though it did little for the grander French strategy in Cambodia and Laos. By the 19th of January, Thai forces were steamrolling south, crossing the Mekong River virtually unopposed. Besides the naval Battle of Koh Chang-recounted at the end of this post, and the aerial campaign, the ground fighting in the Franco-Thai conflict was nearly over.

Aerial Combat in the Franco-Thai Conflict, November-January 1940-41

Aerial combat and strategic bombing was a significant facet of the Franco-Thai conflict as both sides had relatively large reserves of airplanes before the war began. The Royal Thai Air Force (RTAF) fielded both American and Japanese made planes which had been purchased beginning in 1936. Several export models of the Martin B-10 bomber were purchased under the operational name 139WSM. RTAF squadrons were stocked with older Vought V-93 Corsair biplanes, Curtiss Hawk III 'Goshawks', and Curtiss 75N 'Hawks'. Mitsubishi Ki-30 light bombers were deployed as well, making Thailand the only country in the world flying both operational Japanese and American aircraft at this time. The Ki-30 "Nagoyas" were formed into two new squadrons, Foong Bin Phibun Songkhram 1/2, named after the nations' prime minister. Japanese observers helped train these Thai squadrons for combat duty.

The French colonial military in Vietnam had a considerably older and much smaller air force. Opposing the RTAF in the upcoming conflict would be the Armée de l’Air's, Escadrille de Chasse 2/595 and 2/596 aerial regiments. Naval pilots were loaned to these regiments, adding much needed staffing for the French aerial service in Indochina. The speedy Morane-Saulnier MS.406 was the aircraft predominately flown by the French during the conflict. Vichy pilots would of likely had an advantage in experience, though indeed there were few pilots available in Indochina at this time.* Loire 130 flying boats were deployed by the navy for reconnaissance; these aircraft were ideally suited for the coastal and river ways which make Vietnam and neighboring countries so challenging to control from a military perspective. Armée de l’Air pilots flew the outdated Potez 25 for reconnaissance sorties, and Farman 220s and Potez 542s bombers were deployed in scattered and rare night raids against Thai positions. The scarcity of replacement parts made the cannibalization and 'jury-rigging' of aircraft parts essential for the French during their air war with the RTAF. By the wars' end just fourteen Moranes would be operational in the Indochina theatre.

During November-December, several aerial duels were fought over the skies of the disputed border territories. Most of these were indecisive though it seems the French pilots used their experience to at the very least, survive, against the more numerous Thai aircraft. One such duel on 9 December 1940 may illustrate this point. A squadron of three Moranes was attacked by three RTAF Corsairs. At 13,000 feet, French naval pilot Chief Petty Officer André Châtel, outmaneuvered his quarry, shooting down one of the V-93's and damaging another. The Vichy French pilots survived an attack by a lone Curtiss Hawk III on their return trip to the airfield at Dong Hene, claiming one official kill and two other aircraft engaged.

*One of the most experienced French pilots who served in Indochina was Sgt. Williame Labussière (b.1912-1992). A veteran of the Spanish Civil War and the American Volunteer Group in China, Sgt. Labussière and pilot Adj.-Chief Tivollier shot down a Japanese twin-engine bomber on the last day of the Long-San Incident. Fearful of causing even more friction between two Axis Powers, the Vichy French authorities did not officially record the Labussière-Tivollier victory.

RTAF forces showed their willingness to gain total air superiority against the French, launching attacks on airfields at Phnom Pneh, Sisophon and Battambang in November. On 4 January 1941, a Thai squadron attacked Dong Hene airfield in Laos which was home to Escadrille de Chasse 2/595. Six days later, one Ki-30 was shot down by a Morane over Cambodia. The pilot credited for victory was Adj.-Chief Tivollier. RTAF pilot Sgt. Boonyam Bansuksawat and his gunner, Sgt. Boon Suksabi, were killed. The RTAF struck back on 24 January when they shot down a Potez 25 reconnaissance plane escorted by two Moranes.

On 28 January, nine Ki-30s, four Curtiss Goshawks, and three Martin 139's, the latter escorted by three Curtiss Hawks, were dispatched to bomb Siem Reap. This vital French airfield near the temple of Angkor Wat was one of the largest of it's kind in Southeast Asia. Coupled with sorties against Pailin and Sisophon on the same day, the raid on Siem Reap would be the last of the Franco-Thai War. Several French aircraft were destroyed on the ground and vital hangars and repair facilities were made inoperable. One of the Ki-30's piloted by Wing Commander Fuen was photographing the effectiveness of the bombers when he was intercepted by a pair of Moranes that had scrambled to the defense of the base despite the carnage on the runway. A near-comical chase ensued between these three aircraft. Making multiple passes, the Moranes expended both of their twin 7.7 machine guns without even scratching the slow and clumsy Nagoya. The French pilots then simply waved goodbye as they passed Wing Cmdr. Fuen.

Koh Chang: French Gunboats Strike Towards Trat & the conclusion of the Franco-Thai Conflict

Knowing that they had to pressure the invading Thai military forces, the Vichy French scored a small but nevertheless significant naval victory over the Royal Thai Navy at the Battle of Koh Chang, 16-17 January 1941. Remnants of the Marine Indochine were formed into a Vichy French naval task force of gunboats, consisting of the flagship light cruiser Lamotte-Piquet, the Dumont d’Urville, Amiral Charner, and the World War I/inter-war era gunboats Tahure and Marne. Based at Cam Ranh Bay, outside of Saigon, this rag-tag naval group was designated the Groupement occasionel and commanded by Captain Regis Berenger. On 14th January 1941, a squadron of Loire 130's spotted the Thai flotilla comprised of the ships, HTMS Thonburi, Chonburi, and Sri Ayuthia, and the torpedo boats Cholbury, Songkhla, and Trat, anchored near the Koh Chang Islands off the southeastern coast of Thailand. A lone Loire flying boat attacked the Chonburi, strafing the ship and dropping a 330lb pound bomb before their anti-aircraft guns opened up and drove the seaplane off.

The "star" of the Trat archipelago, Koh Chang's shallow coral reefs and small islands offered an ideal mooring spot for ships. The battle itself lasted nearly two hours and was fought in relatively shallow waters for such large ships, the islands offered line-of-sight cover to both sides. Concentrated French fire hit the Thonburi with great effectiveness, killing the captain of the vessel. RTAF aircraft were scrambled including some Nagoyas late in the battle but they had little effect on the outcome. According to one source, RTAF aircraft bombed some of their own ships in a case of mistaken identity. Though both sides sustained significant damage to their vessels, the Thai navy had been crippled. Thirty-six sailors were killed, one of the bloodiest engagements of the conflict for the Siamese, to just eleven French sailors killed. The Chon Buri, Cholbury, and Songkhla were all sunk or crippled, and the flagship cruiser, HTMS Thonburi was later wrecked after being badly damaged at Koh Chang reef.

HTMS Thonburi in action against the Vichy French Navy 17 January 1941

Several nights after the Battle of Koh Chang, a Vichy propaganda broadcast from Saigon acknowledged the battle and the Thai navy stating, "...we cannot forget to pay tribute to the fierce and brave fighting of the Thai naval forces. We wish to pay respect to those who lost their lives in the battle. They died with honor and military pride for their homeland. " The French had lost over 300 killed or wounded and over 200 were captured (180 colonial troops were recorded as MIA) in the fighting from October 1940 to January 1941. The Thai military recorded 108 killed (including thirteen airmen) and 374 wounded soldiers and sailors on their side.

The Franco-Thai War ended following a Japanese mediated ceasefire in Saigon in which the colonial French regime in Southeast Asia was forced to make almost full territorial concessions to Thailand. The Japanese feared that a prolonged conflict would effect their own military and political designs for Southeast Asia. On 8 December 1941, they invaded both Thailand and Malaya, which was apart of the grander strategy in which Pearl Harbor was also attacked. In late December, Thailand was offered generous peace terms and quickly joined the Japanese as a nominal Axis ally. This in turn lead to a lengthy aerial bombardment against Bangkok by Allied airplanes, 1941-1944.

Suggested Further Reading

Moran Saulnier MS.406 Aces, Osprey Aircraft of the Aces 121, Osprey Publishing

Japanese Aircraft In Royal Thai Air Force & Royal Thai Navy Service During WWII By: Jan Forsgren

BJ.2 RTAF Mitsubishi Ki.30 Nagoya www.wings-aviation.ch (Accessed January, 2020)

Paradise in Peril: Western colonial power and Japanese expansion in South-East Asia, 1905-1941 H.T. Bussemaker, (2001).