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Battle of Ko Chang

Battle of Ko Chang
Part of the Franco-Thai War

A map of the battle of Ko Chang
Date 17 January 1941
Location Gulf of Thailand
Result Decisive Vichy French victory

Vichy France

Commanders and leaders
Régis Bérenger Luang Phrom Viraphan 
1 light cruiser
4 avisos
9 aircraft
1 Coastal defence ship
2 torpedo boats
Casualties and losses
1 light cruiser damaged ~36 killed
2 torpedo boats sunk
1 coastal defence ship grounded

The Battle of Ko Chang took place on 17 January 1941 during the Franco-Thai War and resulted in a decisive victory by the French over the Royal Thai Navy. During the battle, a flotilla of French warships attacked a smaller force of Thai vessels, including a coastal defence ship.

In the end, Thailand lost two ships sunk and one heavily damaged and grounded. Within a month of the engagement, the Vichy French and the Thais negotiated a peace which ended the war.


  • Background 1
    • Thai Navy 1.1
    • French Navy 1.2
  • Battle 2
  • Aftermath 3


Thai Navy

Although comparatively small, the Royal Thai Navy had been modernized with the recent acquisition of vessels from both Japan and Italy. The major units of the fleet included two Japanese-built armoured coast defence vessels, which displaced 2,500 long tons (2,500 t) and carried 8-inch (203 mm) guns, two older British-built armoured gunboats with 6-inch (152 mm) guns, 12 torpedo boats, and four submarines.

In addition, the Royal Thai Air Force had in its inventory over 140 aircraft, including relatively modern Mitsubishi Ki-30 (Allied reporting name "Ann") light bombers, which saw extensive service against the French during the war. These aircraft were quite capable of causing severe damage to any French naval mission which might be mounted. Other less capable aircraft in the Thai inventory included P-36 Hawk fighters, 70 Chance-Vought O2U-2 Corsair biplanes, six Martin B-10 bombers, and several Avro 504 trainers.

French Navy


Despite the strength of the Thai forces, the French Governor General of Indochina and Commander-in-Chief Naval Forces, Admiral Jean Decoux, decided to attempt a naval attack on the Siamese fleet. He formed a small squadron called the Groupe Occasionnel on 9 December 1940 at Cam Ranh Bay, north of Saigon. In command he placed Capitaine de Vaisseau Régis Bérenger.

The squadron consisted of the modern light cruiser Lamotte-Picquet, the avisos Dumont d'Urville and Amiral Charner, and the older avisos Tahure and Marne. There was no air cover, except for eight Loire 130 seaplanes based at Ream, which provided reconnaissance. Additional scouting was done by three coastal survey craft, and intelligence gleaned from local fishermen.

Bérenger's squadron began training manoeuvres in Cam Ranh Bay shortly after assembling. On 13 January 1941, Admiral Decoux formally requested that Bérenger lead the squadron against the Thai Navy to support a land offensive planned for 16 January. The land action was meant to force back the Thai ground forces that had been advancing along the coast. Because of the disparate speeds of the French ships, Bérenger sent the slower sloops on ahead, while he remained in Saigon to complete the final elements of the plan.

Several options were being prepared, the Admiralty in France having given its approval to use naval forces to support the army. The final planning meeting on 13 January saw an immediate delay in the execution for 24 hours. Once the plans were completed, Bérenger sailed in Lamotte-Picquet. The delay in starting the operation allowed him to refuel at Cape St. Jacques before his rendezvous with the slower ships at 16:00 on 15 January, 20 mi (17 nmi; 32 km) North of Poulo Condore.

Admiral Decoux's order were simple: "Attack the Siamese coastal cities from Rayong to the Cambodian frontier to force Siamese government to withdraw its forces from the Cambodian frontier". On the evening of 15 January, following a last conference on board the flagship, the squadron weighed anchor at 21:15 and closed the Thai coast at 14 kn (16 mph; 26 km/h), the top speed of the sloops. The French ships remained undetected as they entered the Gulf of Siam, but their quarry was not as fortunate. The Loire 130s from Ream had completed a sweep of the coast from Trat to Sattahip. They had located one coast defence ship and one torpedo boat at Koh Chang, and one gunboat, four torpedo boats, and two submarines at Sattahip.

Their report was forwarded to Marine Headquarters in Saigon, who re-transmitted it to Lamotte-Picquet. Bérenger considered his options and decided on a dawn attack against the Thai ships at Koh Chang. He ignored Sattahip because the sloops would not be able to reach it until later in the day, when the element of surprise would already have been lost. Also, the strength of Sattahip's harbour defences was unknown. The Thai Naval force at Koh Chang was weaker and thus offered a better chance of victory.

Bérenger decided to approach Koh Chang at dawn from the southwest. Because the anchorage at was surrounded by islands and islets, many over 200 metres (660 ft) high, the squadron would separate and use the cover of the islands to concentrate fire on portions of the Thai squadron, while also covering all the avenues of escape. The easternmost channel was the most likely route by which a breakout would be made. It was the most suitable route and where the reconnaissance had placed the largest Thai ships. Lamotte-Picquet would head to the eastern side of the anchorage to block the route, while the sloops blocked the center and pounded the Thai ships there. The smaller French ships would concentrate to the west.


Amiral Charner

The French squadron closed on the anchorage at 05:30 on 17 January. At 05:45, they split into the three groups as planned, the Lamotte-Picquet heading for the eastern part of the anchorage, Dumont d'Urville and Amiral Charner continuing to the central position, and the Tahure and Marne heading for the western side. Conditions were perfect. The weather was fine, the seas calm and almost flat. Sunrise was at 06:30, and the scene was lit only by the first rays of light on the horizon and by the dim moonlight.

A final aerial reconnaissance of the target area had been arranged, using one of the Ream-based Loire 130s. Lamotte-Picquet carried two such aircraft, but these could not be launched due to catapult problems. At 06:05, the Loire 130 overflew the anchorage and reported two torpedo boats. This came as a nasty surprise to the French. Previous reports led them to believe that only one was present, but during the night HTMS Chonburi had arrived to relieve Chantaburi, which was to return to Sattahip later that day for repairs.

Once their presence had been passed to Lamotte-Picquet, the aircraft attempted a bombing attack, but were driven off by a heavy barrage of anti-aircraft fire. The effect of this mission was double edged. The French were now aware of what they faced, but the element of surprise had been wasted and thirty minutes remained until sunrise. Caught napping, the Thais desperately began to raise steam and prepared to slip their anchors. However, both torpedo boats were soon sunk by heavy gunfire from Lamotte-Picquet.

At 06:38, lookouts on Lamotte-Picquet spotted the coastal defence ship HTMS Thonburi heading northwest, at a range of 10,000 metres (11,000 yd). A running battle began, with the fire of both ships frequently blocked by the towering islets. The fire from the Thai ship was heavy, but inaccurate. By 07:15, fires could be seen on Thonburi, which then found herself engaged not only by the cruiser but also the sloops. At the beginning of the engagement, a lucky shot from Lamotte-Picquet killed the captain of Thonburi, Commander Luang Phrom Viraphan, and disrupted her operations. Believing they had a better chance of hurting the smaller French ships, the Thais shifted their fire onto Admiral Charner, which soon found 8-inch (203 mm) salvoes falling around her.

Thonburi shifted fire back to Lamotte-Picquet after a salvo from the French cruiser put her after turret out of action. She soon reached the safety of shallow water, which the French ships could not enter for fear of grounding, but it was too late for the hapless Thais, as Thonburi was burning fiercely and listing heavily to starboard. Her remaining turret was jammed and could not fire unless the manoeuvres of the ship put it in an appropriate position. At 07:50, Lamotte-Picquet fired a final salvo of torpedoes at 15,000 metres (16,000 yd), but lost sight of Thonburi behind an island from which she was not seen to emerge.

At 08:40, Bérenger ordered the squadron to head for home, but this coincided with the start of the expected Thai air attacks. Thai planes dropped several bombs close to Lamotte-Picquet and scored one direct hit; however, the bomb failed to explode. Lamotte-Picquet‍ '​s anti-aircraft guns put up a vigorous barrage and further attacks were not pressed home. The final raid departed at 09:40, after which the victorious French squadron returned to Saigon.


A plaque commemorating the battle

The French left behind them a scene of total devastation. Thonburi was heavily damaged and grounded on a sand bar in the mouth of the Chanthaburi river, with about 20 dead. She was later raised and repaired by the Japanese, survived the war and was used as a training ship until she was retired. The Thai transport HTMS Chang arrived at Ko Chang shortly after the French departed and took Thonburi in tow.

The torpedo boat Chonburi was sunk with a loss of two men, as was HTMS Songhkla with fourteen dead. The survivors were rescued by the torpedo boat HTMS Rayong, the minelayer HTMS Nhong Sarhai, and the fishery protection vessel Thiew Uthok. These three ships, which had been sheltering to the north of Ko Chang, wisely chose not to break cover and were not spotted by the French. On the other hand, the French sailors were elated, believing they had inflicted a defeat as decisive in its way as the Japanese at Tsushima, and had not suffered losses of significance.

Their success is all the more notable when the difficulties of navigating and fighting in such confined waters are considered, and given the courage and tenacity which the Thai sailors exhibited during the action, a fact the French were gracious to acknowledge. In the end, it was all for nought. Five days later the Japanese government offered to arbitrate a peaceful settlement, which soon confirmed the Thai annexations of the territory they had lost to France earlier in the 20th century. Even this interim of peace did not last long, as the Japanese Army invaded Thailand in December of that year as part of its attempt to capture British Malaya. At the conclusion of World War II, Thailand was forced to return all of its short-lived gains to French Indo-China.

Thonburi was later raised by the Royal Thai Navy. She was repaired in Japan and was used as a training ship until she was finally decommissioned. Her guns and deck are preserved as a memorial at the Royal Thai Naval Academy at Samut Prakan.

During the post-action investigations, the Thai navy claimed, based on statements by

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