Over 30,000 Australians served on Bougainville, making it one of our largest campaigns, and yet it remains one of the least understood.
The US Marines landed on Bougainville at the beginning of November 1943 as part of an overall strategy that had been developed to isolate Rabaul. The strategy of "island hopping" was thus evolved, in which strongly defended Japanese positions were bypassed and isolated by establishing Allied airfields and bases to provide the cruicial air and sea support that was needed to cut off the enemy at major bases such as Rabaul.
In late 1944, the Australians replaced American troops on Bougainville and after initially advancing into the interior of the island, the 3rd Australian Division moved south along the coast from Empress Augusta Bay and then south east along the Buin Road. Here they encountered bitter fighting at Slater's Knoll, which lasted from 19 March until 5 April. Meanwhile the 11th Infantry Brigade continued to advance towards the north of Bougainville until the end of January when the Japanese launched a heavy counter-attack near the Genga River. It took hard fighting, with artillery support, to break the Japanese.
The Australians then pushed on and by the end of April had secured the Soraken Peninsula, hemming the Japanese into a small area on the northern tip of the island.
By 1945, Australia's 2nd AIF was diverted into “mopping-up” operations in the Mandated Territories of New Guinea and Bougainville. Karl James' Hard Slog, redresses this imbalance. The nine-month campaign under the control of Lieutenant-General Stanley Savige designed to destroy the Japanese occupation of the island involved 30,000 Australian personnel.
Many of these were 'Militia' units, although many (but not all) for example the 31st/51st Battalion, were re-designated as 2nd AIF units for oveseas service.
The conditions under which the infantry battalions fought were gruelling; "patrolling along stinking, humid jungle tracks and putrid swamps in an intimate, personal war of section patrols and occasional company-size attack".1 In April of 1945, the Japanese mounted a counter-attack, which came close to overrunning the Australians, who had dug in at Slater's Knoll. The arrival of Australian tanks not only broke the Japanese attack but also enabled the Australian advance on Buin, with the aid of artillery and air support.2
Combat operations on Bougainville ended with the surrender of Japanese forces on 21 August 1945. Japan signed the instrument of Surrender on board the USS Missouri in Tokyo Bay on 2 September 1945. From an Australian perspective the campaign resulted in 516 Australians killed and another 1,572 wounded. The toll exacted on the Japanese was far more severe; 8,789 Japanese were killed while the Americans estimated they had killed another 9,890, with many thousands more dying from disease and malnutrition.3 About 23,500 surrendered at the end of the war from an estimated garrison of 40,000 when the Australian II Corps took over operations in November 1944.
The merits of Australia's involvement like much of the fighting in New Guinea and Borneo late in the war, has been the subject of crtical scrutiny. Many felt Australia had been sidelined by its US Ally. However it was perceived by Canberra that it was important to re-assert Australian influence in its protected and mandated territories as a prelude to the defeat of Japan and re-engagement in the island territories with which Australia had been engaged pre-war.
Australian casualties sustained in fighting at Bougainville, which continued until the end of the war, amounted to 2,088, with 516 killed and 1,572 wounded.
 James, Karl. The Hard Slog: Australians in the Bougainville Campaign 1944-1945, Melbourne: Cambridge University Press, 2012, 2.
 James, Karl. The Hard Slog, 3.
 Cambell, Emma (2012). "Bougainville's Hard Slog," Australian War Memorial, viewed 04/04/2016, https://oldsite.awm.gov.au/blog/2012/05/28/bougainvilles-hard-slog/ (oldsite.awm.gov.au).