Despite the many brave and at times desperate actions fought along the Numa Numa trail and on the Bonis Peninsula, both Savige and General Hyakutake knew that the decisive battles on Bougainville would be fought in the south as the Australians pushed towards Buin and Kahili. This was where the Japanese were concentrated and where most of their gardens, vital for their food supplies, were located. Hyakutake would not surrender these lightly. Weeks turned into months as the Australians, harassed by enemy artillery, constantly wet and regularly skirmishing with the Japanese, slowly advanced from Torokina through swamps and jungle tracks. The unrelenting strain of jungle warfare sapped men's nerves and drained their courage. Combat fatigue became a serious problem in two Australian battalions. Commanders too felt the strain as tensions between senior officers boiled over and led to the sacking of a brigade commander.

THE JAPANESE IN THE SOUTHERN SECTOR

As on Buka, Japanese forces had been in Buin since the first days of their invasion, landing in the Buin area on 7 April 1942. The following month a small naval garrison was established around Buin, which later became a large forward shipping base. Airfields were constructed at Kahili, Kieta, Buka and several other areas. These airfields were used for staging aircraft from Rabaul for sorties over the southern Solomons. When it became clear to the commanders in Rabaul in early 1943 that they would lose Guadalcanal, most of Hyakutake's Seventeenth Army was evacuated from Guadalcanal to Shortland and Fauro Islands with the army's headquarters being established around Buin. These forces on Bougainville were reinforced from Rabaul. Enough weapons and equipment were sent to Bougainville for the Seventeenth Army to wage a two-year campaign, although there were only enough food reserves for four months.