The Australian Army was the largest service in the Australian military during World War I. The First Australian Imperial Force (AIF) was the Army's main expeditionary force and was formed from 15 August 1914 with an initial strength of 20,000 men, following Britain's declaration of war on Germany. Meanwhile, the separate, hastily raised 2,000-man Australian Naval and Military Expeditionary Force (AN&MEF), landed near Rabaul in German New Guinea on 11 September 1914 and obtained the surrender of the German garrison after ten days; it later provided occupation forces for the duration of the war. In addition, small military forces based on the pre-war Permanent Forces and part-time Citizen Forces were maintained in Australia to defend the country from attack.