 After the detachment, the main body of the division was converted to the triangular division format in 1943, while the detachment became the 31st division.Late in 1943, Mutaguchi was promoted and replaced as commander of the division by Lieutenant-General Shinichi Tanaka.Transferred to the IJA 33rd Army, and operations in northern Burma, the 18th Division fought against the American-led Chinese divisions advancing on Mogaung and Myitkyina, and against the British Chindits operating behind their lines.