Battle of Ko Chang 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 battleship . 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 . Thai Navy . The Royal Thai Navy had been modernized with the recent acquisition of vessels from Japan and Italy . The major units of the fleet included two Japanese - built armoured coast defence vessels , which displaced 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 bomber s , which saw extensive service against the French . These aircraft in themselves 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 strengths of the Thai forces the French Governor General of Indochina and Commander - in - Chief Naval Forces , Admiral Jean Decoux , decided that the naval mission should go ahead . A small squadron , the Groupe Occasionnel , was formed on 9 December 1940 at Cam Ranh Bay , near Saigon , under the command of " Capitaine de Vaisseau " Régis Bérenger . The squadron consisted of the light cruiser , the avisos " Dumont d ' Urville " PG 77 and " Amiral Charner " PG 81 | 2 , and the older avisos " Tahure " and " Marne " . There was no air cover to speak of , apart from eight Loire 130 seaplanes based at Ream which provided reconnaissance . Additional scouting was provided by three coastal survey craft , and intelligence gleaned from the local fishermen . Bérenger ' s squadron began training manoeuvres in Cam Ranh Bay shortly after coming together . Early in the new year , on 13 January 1941 , Admiral Decoux formally requested Bérenger to send the squadron against the Thais to act in support of a land offensive planned for 16 January . This operation was intended to throw back Thai forces which 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 currently being prepared , the Admiralty in France having recently given its formal blessing to the use of naval forces in support of the army . The final planning meeting of the 13th saw an immediate delay in the execution of the operation for 24 hours . With the plans finalised , Bérenger sailed in " Lamotte - Picquet " , the delay in the start of the operation allowing him to refuel at Cape St . Jacques before the rendezvous with the slower ships at 16 : 00 on the 15th , North of Poulo Condore . The orders from Admiral Decoux 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 the 15th , following a final conference on board the flagship , the squadron weighed anchor at 21 : 15 and closed the Thai coast at , the best 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 two torpedo boats at Ko Chang , and one gunboat , four torpedo boats and two submarines at Sattahip . Their report was sent to Marine Headquarters in Saigon , who re - transmitted the report to the " Lamotte - Picquet " . Bérenger considered his options and decided on a dawn attack on the Thai ships at Ko Chang . He ignored Sattahip because the sloops could not reach there until later in the day , by which time the element of surprise would have been lost . Also , the contribution the harbour defences at Sattahip could make was unknown . Moreover , the force at Ko Chang was the weaker of the two and offered the best chance of victory . Bérenger ' s plan of attack was as follows . The squadron would approach at dawn from the South West . Because the anchorage at Ko Chang was surrounded by islands and islets , many of which were over 200 metres ( 656 feet ) high , the squadron would break up and use the cover of the islands to concentrate fire on portions of the Thai squadron whilst covering all the avenues of escape . The easternmost channel was regarded as the most likely route by which a breakout would be made — this was the most suitable route and was also the area in which the recce report had placed the largest Thai ships . " Lamotte - Picquet " would head to the eastern side of the anchorage to block this route whilst the colonial sloops blocked the centre and pounded the Thai ships there . The smaller French ships would concentrate to the West . Battle . The French squadron closed on the anchorage at 05 : 30 on 17 January . At 05 : 45 , they split into the three groups as planned , " Lamotte - Picquet " heading for the eastern part of the anchorage , " Dumont d ' Urville " and " Amiral Charner " continuing to the central position and " Tahure " and " Marne " heading for the western side . Conditions were perfect — the weather was fine , the seas calm and almost flat . Sunrise was due 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 ships . This came as a nasty surprise to the French — previous reports led them to believe that only one of the torpedo boat was present , but during the night , HTMS " Chonburi " had arrived to relieve " Chantaburi " , which was to return to Sattahip later that day for repairing . Once their presence had been passed to " Lamotte - Picquet " the aircraft attempted an attack of its own using bombs , but was forced off by a heavy barrage of antiaircraft fire . The effect of this mission was double edged — the French were now aware that they faced both the Thai units , but the element of surprise had been wasted and there was still thirty minutes to go until sunrise . Caught napping by the oncoming French the Thais desperately began to raise steam and prepared to slip their anchors , but the torpedo boats were sunk by gunfire from " Lamotte - Picquet " . At 06 : 38 , the lookouts in " Lamotte - Picquet " spotted the coastal defence ship HTMS " Thonburi " , heading northwest , at a range of 10 , 000 meters ( 10 , 936 yards ) . A running battle ensued , 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 by the sloops . In 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 . Soon she reached the safety of shallow water which the French ships could not enter for fear of grounding , but it all came too late for the hapless Thais as " Thonburi " was burning fiercely and listing heavily to starboard . Her remaining turret was manned and hand and could not fire unless the maneuvers of the ship put it in appropriate position . At 07 : 50 , " Lamotte - Picquet " fired a final salvo of torpedoes at 15 , 000 meters ( 16 , 404 yards ) 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 hit , although the bomb failed to explode . " Lamotte - Picquet " s anti - aircraft gun s 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 . Aftermath . 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 and HTMS " Songhkla " also sank with a loss of fourteen dead . The only 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 thus were not observed by the French . The French were elated , for they had inflicted a defeat as decisive in its way as the Japanese at Tsushima . The French 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 which the French were gracious to accept . In the end , though , it was all for nought — five days later the Japanese government offered to arbitrate in the search for a peaceful settlement , and soon confirmed the Thai annexations . Even this state of affairs did not last for long , as Thailand was invaded later that year during the attacks on Malaya , and was forced to return her short - lived gains to France at the end of World War II . " Thonburi " was later raised by the Royal Thai Navy . She was repaired in Japan and was used as a training ship until she was decommissioned . Her gun and deck are placed as a memorial in the Royal Thai Naval Academy , Samut Prakan . During the post - action investigations , the Thai navy claimed , based on claims by Thai sailors and the fisherman around Ko Chang , heavy damage was seen to have been caused to " Lamotte - Picquet " and her fleet . The report claims the crew of " Lamotte - Picquet " spent all of the following night repairing the damage , although it is not revealed how the French ships were observed , given their departure form the site of battle . Such claims are , at best , unsubstantiated and are not reflected in any French documentation , nor the ships logs .