Until World War II Australia did not station any units of its army or air force in the Territory of Papua, nor in the Mandated Territory of New Guinea after the ending of the Australian military administration there in 1921. Ships of the Australian navy made rather infrequent visits to the waters of the territories. A small number of Australian citizens belonged to the New Guinea Volunteer Rifles, which was formed in 1939 and disbanded in 1942. In 1940 a Papuan Infantry Battalion began recruiting. Its private soldiers were Papuans, its officers and some of its non-commissioned officers Australian. The Armed Native Constabulary (ANC) provided recruits, well drilled in the use of rifles, and with knowledge of local conditions and languages that was to be invaluable to the Australian and American armies during the war. Some of the ANC’s NCOs became NCOs in the new force. Later, three New Guinea Infantry Battalions were recruited. In 1943 the four battalions were grouped together under one headquarters as the Pacific Islands Regiment (PIR). Men of the battalions were often detached to act as scouts or reconnaissance patrols with Australian or American infantry units.
The PIR was disbanded in 1946, but raised again in 1951. The officers, and many of the NCOs, once again were Australians. The regiment was under the command of the Australian army, not the colonial Administration. Between 1951 and 1975 the Australian army trained PNGans as NCOs locally, and sent promising recruits to Australian army schools to train as infantry officers and staff officers. It went to considerable trouble to see that no one group of Melanesians dominated the PIR, either as private soldiers or officers, and to inculcate Australian military traditions. These included acceptance by the army of control by civilians: the government of the day. After Independence the PIR became the infantry element of the Papua New Guinea Defence Force but retained its name. Australians continued to act as advisors and instructors.