In the aftermath of the Japanese invasion of Thailand on 7–8 December 1941, the regime of Plaek Phibunsongkhram (Phibun) declared war on the United Kingdom and the United States on 25 January 1942. Seni Pramoj, the Thai ambassador in Washington, refused to deliver the declaration to the United States government. Accordingly, the United States refrained from declaring war on Thailand. Seni, a conservative aristocrat whose anti-Japanese credentials were well established, organized the Free Thai Movement with American assistance, recruiting Thai students in the United States to work with the United States Office of Strategic Services (OSS). The OSS trained Thai personnel for underground activities, and units were readied to infiltrate Thailand. By the end of the war, more than 50,000 Thai had been trained and armed to resist the Japanese by Free Thai members who had been parachuted into the country.