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. Under Lieutenant General
Shōjirō Iida, the IJA 15th Army invaded the southern Burmese province of
Tenasserim. The Fifteenth Army consisted initially of the highly regarded
33rd Infantry Division and the
55th Infantry Division. The latter attacked from northern Thailand, which had signed a treaty of friendship with Japan on December 21, 1941. The 15th Army quickly advanced through southern Burma, defeating the British and Indian
Burma Army in several engagements, and capturing the capital of
Rangoon by March 7, 1942. The Army was reinforced by troops released by the
Fall of Singapore and drove northwards into central Burma, defeating the British
Burma Corps and the
Chinese Expeditionary Force, ultimately driving the
Allies from Burma. During the
following year, the Army remained as a
garrison force in Burma, defeating an Allied offensive in
Arakan and inflicting heavy casualties on a long-range penetration raid under
Orde Wingate. In 1944, the Fifteenth Army became part of the
Burma Area Army. Lieutenant General Iida was posted back to Japan and Lieutenant General
Renya Mutaguchi took command. He forcefully advocated an offensive against British India. The offensive,
Operation U-Go, was launched in March. As a result of poor logistics and Mutaguchi's underestimation of the difficulties, the Fifteenth Army was almost destroyed in the
Battle of Imphal and the
Battle of Kohima. Mutaguchi, his chief of staff, and several other officers were removed in the aftermath, and Lieutenant General Shihachi Katamura was assigned to command. As the
monsoon season ended, the remnants of the Fifteenth Army attempted to forestall an Allied offensive into Burma by
withdrawing behind the
Irrawaddy River. They were unable to prevent British and Indian troops from securing bridgeheads across the river, and the army was weakened by losses and detachments to other parts of the front. Once
Mandalay was captured, the Fifteenth Army could only retreat southwards, badly disorganised and was further depleted in the
failed Japanese breakout of the
Pegu Yomas in July and August 1945. The remnants of the Fifteenth Army were later absorbed as a subsidiary unit of the
18th Area Army. The 15th Army was
demobilized at
Lampang Province in Thailand, on the
surrender of Japan in 1945. ==List of Commanders==