On 14 August 1914, soon after the First World War began, Elliott was given the same rank in the Australian Imperial Force (AIF), and command of the 7th Infantry Battalion, one of four Victorian battalions in Colonel James Whiteside McCay's 2nd Infantry Brigade. Elliott's first action was to ask Major Walter McNicoll to be his second in command, a position McNicoll readily accepted. He then supervised the raising of his battalion. Three of his eight companies were drawn from the northern suburbs of Melbourne, but the other five came mainly from central Victoria. He took particular care over the selection of officers. The newly formed battalion marched from Victoria Barracks to the training camp at Broadmeadows, Victoria, on 19 August. Elliott believed that Australians would take readily to military discipline if the reasons for it were properly explained. McCay was disturbed at the numbers of men without prior militia training that were being enlisted, but some of the battalion's recruiting area had no militia units. Instead, Elliott relied on the quality of the militia's officers and non-commissioned officers to produce well-trained soldiers.