At the outbreak of the Second World War, the 8th Battalion undertook a period of continuous training in 1939 and then again in 1940 as part of the general plan to increase the readiness of Australia's home defences. At this time it was assigned to the 6th Brigade along with the 7th and 38th Battalions. Following Japan's entry into the war in December 1941 the battalion was moved to Darwin where it was transferred to the 23rd Brigade, which had been previously made up of units of the Second Australian Imperial Force but which had largely been destroyed in Malaya and subsequently reformed as a Militia formation consisting of the 7th, 8th and 27th Battalions. The 8th remained in Darwin on defensive duties until September 1943 when its personnel were given a months leave in Melbourne before moving to the Atherton Tablelands in Queensland for training prior to deployment overseas. In May 1944, they moved to Lae, where they remained until October 1944 when the 23rd Brigade relieved the American forces garrisoning the Outer Islands. During this time the 8th Battalion were stationed on Emirau Island, where a number of its personnel crewed United States Navy PT boats and took part in raiding operations around New Britain and New Ireland.