During the second half of World War I, the First Australian Imperial Force experienced a shortage of men as the number of men volunteering to fight overseas declined and the casualty rate increased. At the time, military service within the Commonwealth of Australia and its territories was compulsory for Australian men, but that requirement did not extend to conflict outside of Australia. In 1916, Prime Minister Billy Hughes called a plebiscite to determine public support for extending conscription to include military service outside the Commonwealth for the duration of the war. The referendum, held on 28 October 1916, narrowly rejected the proposal. A second plebiscite, held a year later on 20 December 1917, also failed (by a slightly larger margin) to gain a majority.