Japanese Army in World War II

Japan’s successful conquest of the South Pacific and Southwest Asia from December 8, 1941 through to June 1942 saw few setbacks. The commencement of the Pacific War (Taiheiyo Senso), coupled with the China Incident (Shina Jihen) on-going since 1931, was what Japan called the Greater Southeast Asia War (Dai Toa Senso Senkum)—more commonly known as World War II. The Southern Operations that began the Pacific War comprised a complex series of widely scattered operations aimed at neutralizing American, Commonwealth, and Dutch forces, seizing regions rich in economic resources, and securing an outer defense line for the “Greater Southeast Asia Co-prosperity Sphere” (Dai Toa Kyoei-Ken).

The American bastion of the Philippines, the Netherlands East Indies (NEI), and Commonwealth possessions of the Gilbert, Bismarck, and Solomon islands were occupied, and troops were landed on Eastern New Guinea. Commonwealth forces were driven from Malaya, Thailand and most of Burma, and Hong Kong and Singapore were taken by the Japanese. All of the objectives were secured with light to moderate losses well within the projected timeframe, with the notable exception of the Philippines. Rather than securing the vast archipelago within the allotted 50 days, it required five months. In addition, the occupation resulted in heavy losses and required reinforcements to be sent in.

The Southern Operation, or Z Operation, was conducted by the Southern Army under the command of Gen Count Terauchi Hisaichi (also listed as Juichi) headquartered in Saigon, French Indochina. Under his command were four armies, 11 divisions, and six brigade equivalents plus substantial support, service, and air units. Additional units were deployed during the course of the Southern Operation.

At the beginning of the war the Imperial Japanese Army (Dai Nippon Teikoku Rikugun, or simply Kogun, herafter abbreviated to IJA) consisted of 51 divisions and 59 brigade equivalents. Surprisingly only nine new divisions had been organized in 1940 and one in 1941, with most intended for China rather than in preparation for facing the Allied counteroffensive. Numerous brigade equivalents, service, and air units had been raised though, as were independent mixed brigades (IMBs) and garrison units to secure occupied territories. Only seven infantry divisions were activated in the spring of 1942.

With the Philippines, Malaya, NEI, Bismarcks, and the Solomons secured, the Imperial Japanese Navy (IJN) planned further conquests, having longer-ranged goals than the IJA. Rabaul on New Britain would be a base from which to continue the conquest. The IJA thought of Rabaul only as an out-guard for the naval base at Truk in the Carolines. The IJN, in cooperation with the IJA, desired to seize Port Moresby on the south coast of Papua in May; Midway and the western Aleutian Islands in June, hoping for a decisive engagement with the US Pacific Fleet; New Caledonia in July; and Fiji and Samoa in August. The goal was to break the Southern Lifeline between America and Australia. Future plans were even more ambitious, with proposals to invade Hawaii, northern Australia, and Ceylon.