The Battle of Ko Chang took place on 17 January 1941 during the Franco-Thai War in which a flotilla of French warships attacked a smaller force of Thai vessels, including a coastal defence ship. The battle resulted in a tactical victory by the French Navy over the Royal Thai Navy although the strategic result is disputed. The Japanese intervened diplomatically and mediated a ceasefire which was in Thailand's favor as all disputed territories in French Indochina were ceded by Vichy France to Thailand. In the end, two Thai ships were sunk and one was heavily damaged. Within a month of the engagement, the French and the Thais negotiated a peace which ended the war.

Vichy France, officially the French State, was the French rump state headed by Marshal Philippe Pétain during World War II. It was named after its seat of government, the city of Vichy. Officially independent, but with half of its territory occupied under the harsh terms of the 1940 armistice with Nazi Germany, it adopted a policy of collaboration. Though Paris was nominally its capital, the government established itself in the resort town of Vichy in the unoccupied "free zone", where it remained responsible for the civil administration of France as well as its colonies. The occupation of France by Nazi Germany at first affected only the northern and western portions of the country, but in November 1942 the Germans and Italians occupied the remainder of Metropolitan France, ending any pretence of independence by the Vichy government.