In October 1941, the 146th Infantry Regiment and 2nd Battalion of the 56th Field Artillery Regiment were re-organized as the "56th Independent Mixed Regiment". It departed from Palau on 16 December 1941 and landed in Davao City on 17 December 1941 and sailed again on 7 January 1942 to Tarakan. Afterwards, it was slated for the Borneo invasion. On 21 January 1942 it sailed from Tarakan to Balikpapan and on 19 February 1942, the Sakaguchi detachment was sent to eastern Java, arriving on 1 March 1942, to cooperate with the 48th Division. The Sakaguchi detachment is credited with the capture of Cilacap Regency port after a 400 km long march. The detachment was merged back into the 56th Division in April 1942. With the Pacific War becoming imminent, the 56th Division was fully mobilized in November 1941. Although initially the 56th division was slated as reinforcements for the Japanese invasion of Malaya, the rapid cessation of British resistance have resulted in division been attached to 25th Army and sent to Burma in March 1942, landing in Rangoon and participating in the Battle of Toungoo. The 56th Division linked with the 55th Division in Toungoo on 28 March 1942. Its reconnaissance elements forced the Chinese to evacuate the city opening the way to the east. Later the 56th Division flanked the allied line to the east, by advancing through the mountains to the Salween River in the Karenni States. The Division defeated the Chinese 6th Corps in the Karen Hills area battles of Mawchi on 13 April 1942, Bawlake, Bato, Taunggyi and Loikaw on 20 April 1940, and forced their retreat eastward to Yunnan. Advancing north through the Shan States the 56th Division defeated elements of the Chinese 65th Corps to take the city of Lashio on the Burma Road. The fall of Lashio to the 56th Division on 29 April 1942 cut off much of the local Chinese Army from China and compelled the Allies to evacuate Burma. The Division advanced into Yunnan in pursuit of the Chinese but were halted at the Battle of Salween River by the Chinese 36th and 88th Divisions on 31 May 1942. From May 1942, the 56th Division performed mostly garrison duties on the Yunnan border. The 113th Infantry Regiment was mostly in Yunnan except for the 3rd Battalion in Longling County. The 148th Infantry Regiment was stationed in Tengchong. The heavy fighting resumed in January 1944 with the Battle of Lashio, as part of Battle of Northern Burma and Western Yunnan campaign in 1944. During the campaign, the division's 114th Infantry Regiment, borrowed from the 18th Division, was credited with shattering Merrill's Marauders in the Siege of Myitkyina in May–August 1944 and in delaying the 15:1 superior Chinese forces and inflicting heavy Chinese casualties during the Battle of Mount Song. Faced with numerically and better equipped enemy in an attrition battle, the 56th Division suffered heavy losses. The remnants of the division were removed from the front line in October 1944, and on the day of the surrender of Japan, 15 August 1945, on the border between South Burma and Thailand.
