Date visited 7/11 Oct 2019
The Battle of Koh Chang took place on 17 January 1941, when a Vichy French squadron, led by the light cruiser Lamotte-Picquet defeated a Siamese squadron, including the coast defence ship Thonburi. I came across two memorials to the battle in Thailand - a new one at the southern end of the island of Koh Chang (which unfortunately was closed when I went there), and one on the mainland between the Koh Chang ferry, and Trat airport.
References:
Guilini, J 1990. A Resume of the Battle of Koh-Chang, 17 January 1941. Warship International, 27 (2), 135-140.