 Following the outbreak of World War II , due to the provisions of the Defence Act ( 1903 ) which precluded deploying the Militia outside of Australian territory , the government decided to raise an all volunteer force for overseas service , known as the Second Australian Imperial Force ( 2nd AIF ) . As such while the Militia would provide a cadre for this force , its main role was to provide training to conscripts as part of the compulsory training scheme which was re @-@ established in early 1940 . During this time the Militia were called up in cohorts for periods of continuous training and the 27th Battalion , along with the rest of the 3rd Brigade , undertook garrison duties in South Australia as well as running number of training camps designed to increase the nation 's defences in case of war in the Pacific . With Japan 's entry into the war following the attacks on Pearl Harbor and Malaya , the battalion was mobilised for wartime service on 9 December 1941 and transported to Darwin in northern Australia where it formed part of the garrison force to defend against possible Japanese attack . During this time it was based at Winnellie and took part in building defences in the north . 
