At the outbreak of the First World War Germany administered several territories in the south and central Pacific and operated a small fleet, including the armoured cruisers Scharnhorst and Gneisenau, out of Tsingtao in China. In order to prevent harbours in these territories being used by the fleet, Australia and New Zealand were requested by Britain, on 6 August 1914, to dispatch forces to occupy them.

A force of New Zealand troops, escorted by HMA Ships Australia and Melbourne, HM Ships Psyche, Philomel, Pyramus, and the French cruiser Montcalm landed on the Samoan island of Apia on 30 August 1914. German Samoa was surrendered without a fight. Australia was subsequently dispatched to destroy the German radio station on Nauru. On arriving there on 9 September, the radio station was found to have already been disabled by its staff and Nauru was also surrendered without opposition.

The major Australian effort was directed at German New Guinea, in particular New Britain. On 11 September 1914, a force consisting of HMA Ships Australia, Sydney, Encounter, Warrego, Yarra, Parramatta, submarines AE1 and AE2, a store-ship, three colliers, and the Berrima with the Australian Naval and Military Expeditionary Force embarked, arrived off Rabaul. On the same day, naval troops were landed by Sydney, and by Warrego and Yarra, at Herbertshohe and Kabakaul, respectively, to search for German radio stations. The second force was involved in a series of short contacts with German forces on its march inland to Bitapaka and finally occupied the radio station there around 7 pm.

Rabaul was occupied, unopposed, by troops from Berrima on 12 September. The German administration fled inland to Toma, but faced with an advance by Australian troops from Herbertshohe, supported by gunfire from Encounter, they surrendered German New Guinea on 17 September. In coming months Australian vessels and troops were dispatched to search and occupy Germany's other territories including the New Guinea mainland, New Ireland, the Admiralty Islands, the Western Islands, Bougainville, and the German Solomons.