 The Japanese naturally wished to cut this link.The Southern Expeditionary Army Group under overall command of Hisaichi Terauchi was responsible for all military operations in the South-East Asia.The Japanese Fifteenth Army, commanded by Lieutenant General Shojiro Iida, was initially assigned the mission of occupying northern Thailand, which had signed a treaty of friendship with Japan on 21 December 1941, and attacking the southern Burmese province of Tenasserim across the Tenasserim Hills.