British North Borneo was the site of the last operation conducted by the 9th Australian Division during the Second World War. The ultimate objective of the operation, codenamed OBOE 6, was the liberation of British North Borneo, which had been occupied by the Japanese since 1942. Its immediate military purpose, however, was to secure Brunei Bay for use as a base by the British Pacific Fleet. On 10 June 1945 the 24th Brigade of the 9th Australian Division landed on Labuan Island at the mouth of the bay, while its sister brigade – the 20th – landed on the Borneo mainland at Brunei point. The landings were virtually unopposed. The 24th subsequently cleared Labuan and crossed into British North Borneo, while the 20th Brigade leapfrogged down the Brunei (a British-protected state) coast, utilising watercraft as its main form of transport. These movements resulted in a series of small-scale but relatively costly engagements. The Australian forces remained active until the end of the war on 15 August 1945. OBOE 6 killed 114 Australians and approximately 1,400 Japanese.
The 9th Division was heavily involved in reconstructing British North Borneo from July onwards and rebuilt and re-established a considerable amount of civil infrastructure. The division developed a warm relationship with the local people and its efforts were recognised by the incorporation of the division's colour patch in the coat of arms of the new Colony of British Borneo. These arms were used until British Borneo became the Malaysian state of Sabah in 1963.