Contributor: C. Peter Chen
On 25 Sep 1940, France surrendered Indochina to Japan after two months of political intrigue and a brief military campaign. Seeing the weak responses from France and other powers, Thai Prime Minister Major General Plaek Pibulsonggram saw the opportunity to regain territory in Laos and Cambodia that Thailand had lost to the French in the early 1900s. Border skirmishes began in Oct 1940, quickly escalating to air raids on Vientiane in Laos and on Sisophon and Battambang in Cambodia; French Air Force equipment were outdated and could not adequately defend against Thai attacks.
On 9 Dec 1940, French Admiral Jean Decoux formed the small naval squadron Groupe Occasionnel at Cam Ranh Bay, near Saigon, French Indochina to guard against any aggressive action the Thai Navy might take. The force was placed under Capitaine de Vaisseau Régis Bérenger and was consisted of light cruiser Lamotte-Picquet, aviso Dumont d'Urville, aviso Amiral Charner, aviso Tahure, and aviso Marne. The squadron was supported by several small coastal survey craft and seaplanes for reconnaissance.
The ground invasion began in early Jan 1941 when the Thai Burapha Army and Isan Army, overruning French and French colonial positions in Laos while exerting pressure on defensive lines in Cambodia. At dawn on 16 Jan 1941, the French launched a major counterattack, pushing back Thai forces, but could not push forward as intelligence on Thai positions was lacking.
On the same day of the French counterattack, the Groupe Occasionnel squadron, moving toward the Thai-Cambodian border, detected two small concentrations of Thai naval forces. The group at Ko Chang island was consisted of coastal defense ship Thonburi and two torpedo boats, while the group at Sattahip further north was consisted of one gunboat, four torpedo boats, and two submarines. Bérenger opted to attack the former at dawn on the next day; with Ko Chang being the closer target, Bérenger thought he would achieve surprise by striking sooner rather than later. On 17 Jan, at 0545 hours, the squadron reached the Ko Chang area. Moving amidst the many small islets, the French ships were able to reach optimal positions of attack before sunrise at 0630 hours. Lamotte-Picquet opened fire at 0638 hours, and Thonburi fired back with her four 8-inch (or 203-millimeter) guns shortly after. By 0715 hours, fires were observed aboard Thonburi; what the French did not know was that one of the shells that had hit Thonburi struck close to the bridge and had killed the captain Commander Luang Phrom Viraphan. At 0750 hours, Lamotte-Picquet fired a salvo of torpedoes at the distance of 15,000 meters at Thonburi, which by this time was in full flight. Shortly after, Thonburi disappeared behind an islet. The two Thai torpedo boats present, Chonburi (2 were killed) and Songhkla (14 were killed), were both destroyed during the battle. At 0840 hours, Bérenger ordered the squadron to return to port, giving up the chase. En route home, Thai aircraft made several attack runs at the squadron, scoring one hit on Lamotte-Picquet, but the bomb failed to detonate. The French ships experienced no more air attacks after 0940 hours. Thonburi, which had grounded on a sand bar at the mouth of the Chanthaburi River, suffered heavy damage and 20 killed, but would be kept afloat for later repairs.
In late Jan 1941, the Conference for the Cessation of Hostilities was sponsored by Japan to end the conflict. The cease fire was signed aboard Japanese cruiser Natori at Saigon, French Indochina on 31 Jan 1941. On 9 May, a formal peace treaty was signed in Tokyo, Japan, officially ending the war. The Japanese-brokered peace treaty forced France to cede northwestern Cambodia and two Lao enclaves to Thailand; in appreciation, Prime Minister Pibulsonggram secretly pledged military support for Japan should Japan engage in a war with the United Kingdom.
The war saw the French suffering 321 dead or wounded, 178 missing, and 222 captured; the majority of the losses were French, Vietnamese, Lao, or Cambodian, with a small number being North African. The greatest loss suffered by the French was in the domain of the air force, which saw 30 of the already small 100-aircraft fleet being destroyed. Thailand suffered 108 killed, 374 wounded, and 21 captured.
After the war, France forced Thailand to return the territories gained during the Franco-Thai War by threatening to veto Thailand's entry into the United Nations. In Oct 1946, Thailand returned the territories to France.
Franco-Thai War Timeline
|9 Dec 1940||The French Groupe Occasionnel squadron was formed in French Indochina, consisted of a light cruiser and four avisos.|
|8 Jan 1941||Royal Thai Air Force aircraft attacked French positions at Siem Reap and Battambang in Cambodia, French Indochina.|
|13 Jan 1941||Admiral Jean Decoux ordered Capitaine de Vaisseau Régis Bérenger to plan an attack on the Thai Thai Navy within the coming days.|
|15 Jan 1941||Ships of the French Groupe Occasionnel squadron made rendezvous at 1600 hours 20 miles north of Poulo Condore (Con Dao) archipelago south of French Indochina, and began moving toward the Thai-Cambodian border at 2115 hours.|
|16 Jan 1941||French troops launched a successful counterattack against Thai troops at the villages of Yang Dang Khum and Phum Preav in Cambodia, French Indochina, but poor intelligence forced the French to back off from any territory gained. The Thais were unable to pursue the retreating French, as their forward tanks were kept in check by the guns of the French Foreign Legion.|
|17 Jan 1941||A French naval squadron attacked the Thai anchorage at Ko Chang island near the Thai-Cambodian border, sinking two gunboats, damaging a coastal defense ship, and killing 36 men.|
|24 Jan 1941||Thai aircraft bombed the airfield at Angkor near Siem Reap, Cambodia, French Indochina; the resulting dogfights would be the final air battle of the Franco-Thai War.|
|28 Jan 1941||B-10 medium bombers of the Thai 50th Bomber Squadron, escorted by 13 Hawk 75N fighters of the Thai 60th Fighter Squadron, bombed Sisophon, Cambodia, French Indochina. The effective date of the cease fire to be signed on 31 Jan 1941 would backdate to this date.|
|31 Jan 1941||The cease fire ending the Franco-Thai War was signed aboard Japanese cruiser Natori at Saigon, French Indochina, effective 28 Jan 1941.|
|11 Mar 1941||Japan dictated that France would return parts of Cambodia and Laos, which the French had gained from Thailand about 40 years prior, to Thailand.|
|9 May 1941||A peace treaty was signed between Thailand and France in Tokyo, Japan, officially ending the Franco-Thai War; the French was coerced by the Japanese to relinquish their hold on the disputed border territories.|
|30 Sep 1941||Representatives of France and Thailand further defined the boundaries between Thailand and French Indochina per the 9 May 1941 peace treaty.|
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Thomas Dodd, late 1945