The AIF's first experience of warfare on the Western Front was also the most costly single encounter in Australian military history. In July 1916, at Fromelles, in a diversionary attack during the Battle of the Somme, the AIF suffered 5,533 killed or wounded in 24 hours. Sixteen months later, the five Australian divisions became the Australian Corps, first under the command of General Birdwood, and later the Australian General Sir John Monash. Two bitterly fought and divisive conscription referendums were held in Australia in 1916 and 1917. Both failed, and Australia's army remained a volunteer force. Monash's approach to the planning of military action was meticulous, and unusual for military thinkers of the time. His first operation at the relatively small Battle of Hamel demonstrated the validity of his approach and later actions before the Hindenburg Line in 1918 confirmed it.