 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 , an Australian @-@ born officer with previous part @-@ time military service ; the 2nd , under Colonel James Whiteside McCay , an Irish @-@ born 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 . The initial response for recruits was so good that in September 1914 the decision was made to raise the 4th Infantry Brigade and 2nd and 3rd Light Horse Brigades . The 4th Infantry Brigade was commanded by Colonel John Monash , a prominent Melbourne civil engineer and businessman . The AIF continued to grow through the war , eventually numbering five infantry divisions , two mounted divisions and a mixture of other units . As the AIF operated within the British war effort , its units were generally organised along the same lines as comparable British Army formations . However , there were often small differences between the structures of British and Australian units , especially in regards to the AIF infantry divisions ' support units . 
