turned into the small–scale Franco-Thai War between Vichy France and Thailand. Thai forces dominated the war on the ground and in the air, but the Thai Navy suffered a crushing naval defeat at the battle of Ko Chang. The Japanese then stepped in to mediate the conflict. The final settlement thus returned most of the disputed areas in Laos and Cambodia to Thailand. World War II Phibun's prestige was so increased that he was able to bask in a feeling of being truly the nation's leader. To celebrate the occasion, he promoted himself to field marshal, skipping the ranks of lieutenant general and general. This caused a rapid deterioration of relations with Britain and the United States. In April 1941 the United States cut off petroleum supplies to Thailand. Thailand's brief period of glory came to an end on 8 December 1941 when Japan invaded the country along its southeastern coastline and from Cambodia. After initially resisting, the Phibun regime gave in and allowed the Japanese to pass through the country to attack Burma and invade Malaya. Convinced by the Allied defeats of early 1942 that Japan was winning the war, Phibun decided to form a military alliance with Imperial Japan. In return, Japan allowed Thailand to invade and annex the Shan States and Kayah State in northern Burma, and resume sovereignty over the sultanates of northern Malaya which had been surrendered in the Anglo-Siamese Treaty of 1909 with Britain. In January 1942 Phibun declared war on Britain and the United States, though the Thai Ambassador to the United States, Seni Pramoj, refused to deliver it to the state department. Seni denounced the Phibun regime as illegal and formed a Seri Thai Movement in Washington. Pridi, now serving in the role of an almost powerless regent, led the resistance movement inside Thailand, while former Queen Ramphaiphanni was the nominal head in Great Britain. Secret training camps were set up in remote areas, the majority by the populist politician Tiang Sirikhanth in the northeast region of the country. There were a dozen camps alone in Sakhon Nakhon Province. Clandestine airfields also appeared in the northeast, where Royal Air Force and United States Army Air Forces planes brought in supplies, as well as Special Operations Executive, Office of Strategic Services, and Seri Thai agents, at the same time evacuating escaped prisoners of war. By early 1945, Thai air force officers were performing