Under Lieutenant General Shōjirō Iida, the IJA 15th Army invaded southern Burmese province of Tenasserim. The 15th Army consisted initially of the highly regarded 33rd Infantry Division and the 55th Infantry Division, which 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, Rangoon by 7 March 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 forces, ultimately driving the Allies from Burma.
For 1944, Fifteenth Army became part of the Burma Area Army. Lieutenant General Iida was posted back to Japan and Lieutenant General Renya Mutaguchi took command of Fifteenth Army. 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 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. Lieutenant General Shihachi Katamura took command. As the monsoon season ended, the Army attempted to forestall an Allied offensive into Burma by withdrawing behind the Irrawaddy River. They were unable to prevent British and Indian troops 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 Army could only retreat southwards, badly disorganised.
The remnants of Fifteenth Army were later absorbed as a subsidiary unit within the Japanese 18th Area Army.
|1||Lieutenant General Shōjirō Iida||5 November 1941||18 March 1943|
|2||Lieutenant General Renya Mutaguchi||18 March 1943||30 August 1944|
|3||Lieutenant General Shihachi Katamura||30 August 1944||15 August 1945|
|1||Lieutenant General Haruki Isayama||14 November 1941||1 December 1942|
|2||Lieutenant General Eitaro Naka||1 December 1942||18 March 1943|
|3||General Hideyoshi Obata||18 March 1943||26 May 1943|
|4||Lieutenant General Todai Kunomura||26 May 1943||22 September 1944|
|5||Major General Gonpachi Yoshida||22 September 1944||September 1945|