For the Japanese Army, 1943 was a pivotal year for its operations in the South Pacific. The Japanese had initiated the Pacific War in December 1941 with highly successful offensive campaigns against the British, Americans, Dutch and Australians, but its offensive momentum was blunted at Midway in June 1942, and Japan's strategic offensive was finally halted on Guadalcanal and eastern New Guinea during the second half of that year. Through the first half of 1943, the Japanese Army sought a new strategy in order to cope with the new situation in the South Pacific. The end result was the adoption on 30 September 1943 of the so-called ‘Absolute National Defence Zone’ concept, which marked a transition to the strategic defensive. That strategy was, however, not adopted overnight. Between the twin defeats of Guadalcanal and Buna and the formal adoption of the strategic defensive, Japanese military leaders and staff officers had many mental struggles as they tried to cope with the situation as it continued to change, often to the detriment of Japan.

This chapter will provide an overview of Japan's road to the strategic defensive, from early 1943 to autumn of that year. The focus will primarily be on the Japanese Army, which in 1942 became ever more committed to the fighting in the South Pacific, a region to which it had not expected to make any great commitment of forces as late as the opening of the Pacific War. This chapter will also focus more on the strategic and operational decisions made by the Army Section, Imperial General Headquarters in Tokyo, as well as by the Eighth Area Army and Eighteenth Army in the South Pacific. The Imperial Navy's strategic and operational decisions in 1943 leading up to the adoption of the ‘Absolute National Defence Zone’ concept will also be reviewed, but primarily in the context of how the Navy's views differed from the Army's. Finally, some details of the fighting at the tactical level will be covered, but only to enlighten Japanese operational and strategic decisions.