Following the outbreak of war Australian forces moved quickly to reduce the threat to shipping posed by the proximity of Germany 's Pacific colonies . The Australian Naval and Military Expeditionary Force ( AN & MEF ) , a 2000 @-@ man volunteer force — separate from the AIF — and consisting of an infantry battalion plus 500 naval reservists and ex @-@ sailors , was rapidly formed under the command of William Holmes . The objectives of the force were the wireless stations on Nauru , and those at Yap in the Caroline Islands , and at Rabaul in German New Guinea . The force reached Rabaul on 11 September 1914 and occupied it the next day , encountering only brief resistance from the German and native defenders during fighting at Bita Paka and Toma . German New Guinea surrendered on 17 September 1914 . Australian losses were light , including six killed during the fighting , but were compounded by the mysterious loss offshore of the submarine AE1 with all 35 men aboard .