Units responsible to Mutaguchi were involved in the Marco Polo Bridge Incident of 7 July 1937, which helped launch the Second Sino-Japanese War.

This division was active in the invasion of Malaya in the early stages of the war, and Mutaguchi himself was wounded during the Battle of Singapore in February 1942.

After the fall of Singapore, the 18th Division was transferred to the Philippines to reinforce units pushing the remaining American forces down the Bataan Peninsula.

Mutaguchi was then made commander of the Fifteenth Army from March 1943, and strongly pushed forward his own plan to advance into Assam, leading to the Battle of Imphal.

[4] British historian Frank McLynn characterized Mutaguchi as "eccentric," "reckless," and a "fanatic," citing his decision to provide his soldiers with only twenty days of food for the nearly four month-long Battle of Imphal.

[5] This led to catastrophic loss of life for the Imperial Japanese Army prior to the battle, losing 55,000 out of his 90,000 men to starvation.