The Japanese 15th Army was formed on November 9, 1941, as a component of the Southern Expeditionary Army Group for the specific task of invading the British colony of Burma. To do this the army, then based in Indo-China, needed to transit through Thailand. On December 8, 1941, the 33rd and 55th Divisions of the army spearheaded by the Imperial Guard invaded Thailand overland from what is now Cambodia. The invasion was supported by landings on the coast to the south of Bangkok by the army's 143rd Infantry Regiment. Fighting lasted only a few hours before the Thai government ceded access.