In late 1944 , as part of plans to free US troops up for the Philippines campaign , the Australian II Corps — consisting of mainly Militia troops under the command of Lieutenant General Stanley Savige — took over responsibility for Allied operations on Bougainville from the American XIV Corps . Australian forces began arriving on the island between November and December 1944 , initially establishing themselves around the US base at Torokina . Due to inaccurate intelligence , Savige mistakenly believed that the Japanese forces on the island numbered just 17 @,@ 500 men , and he consequently decided that the Australians would pursue an aggressive campaign to clear the Japanese from Bougainville in order to free their troops for subsequent operations elsewhere , rather than maintaining the defensive posture the US forces had adopted . However , Allied estimates of Japanese strength were later found to be grossly inaccurate and after the war it was found that the number of Japanese on the island at this time was closer to 40 @,@ 000 .