 The AIF began forming shortly after the outbreak of war and was the brain child of Bridges and White . Upon formation , the AIF consisted of only one infantry division , the 1st Division , and the 1st Light Horse Brigade . The 1st Division was made up of the 1st Infantry Brigade under Colonel Henry MacLaurin ; the 2nd , under Colonel James Whiteside McCay , an Australian politician and former Minister for Defence ; and the 3rd , under Colonel Ewen Sinclair @-@ Maclagan , a British regular officer seconded to the Australian Army before the war . The 1st Light Horse Brigade was commanded by Colonel Harry Chauvel , an Australian regular , while the divisional artillery was commanded by Colonel Talbot Hobbs . 
