Fighting in the northern sector continued during this time also , and although preparations in the south for the final advance towards Buin continued into August , combat operations on the island ceased as the war came to an end before these were completed . As a result , the final Australian operations on Bougainville took place on the Ratsua front in the northern sector , where the Australians had been conducting a holding action since the failed landing at Porton Plantation had forced them to abandon plans for an advance into the Bonis Peninsula . By mid @-@ August , however , following the dropping of two atomic bombs on Hiroshima and Nagasaki and Japan 's subsequent unconditional surrender , a cease fire was ordered on the island and although it were minor clashes following this , it spelt an end to major combat operations .