introduced in mid-1942, when all men aged 18–35 and single men aged 35–45 were required to join the Citizen Military Forces (CMF). Volunteers with the Australian Imperial Force (AIF) scorned CMF conscripts as "chocolate soldiers", or "chockos", because they were believed to melt under the conditions of battle, or it might be an allusion to George Bernard Shaw's Arms and the Man in which Bluntschli filled his backpack with chocolate bars, rather than ammunition. However, several CMF Militia units fought under difficult conditions, suffered extremely high casualties in 1942 and slowed the Japanese advance on the Kokoda Track in New Guinea, then an Australian territory. The Papuan campaign of 1942 led to a significant reform in the composition of the Australian Army. During the campaign, the restriction banning CMF personnel from serving outside Australian territory hampered military planning and caused tensions between the AIF and CMF. In late 1942 and early 1943, Prime Minister John Curtin overcame opposition within the Australian Labor Party to extending the geographic boundaries in which conscripts could serve to include most of the South West Pacific, and the necessary legislation was passed in January 1943. The 11th Brigade was the only CMF formation to serve outside Australian territory, however, when it formed part of Merauke Force in the Dutch East Indies in 1943 and 1944. Korean War In 1951, during the Korean War, national service was introduced under the National Service Act 1951. All Australian males aged 18 had to register for 176 days training (99 days full-time) and two years in the CMF. Later, the obligation was 140 days of training (77 days full-time) and three years of service in the CMF. The regular military forces were kept as voluntary. In 1957, the system was changed to emphasise skill rather than numbers. The system was ended in 1959. Vietnam War In 1964, compulsory national service for 20-year-old males was introduced under the National Service Act 1964. The selection of conscripts was made by a sortition or lottery draw based on date of birth, and conscripts were obligated to give two years of continuous full-time service, followed by a further three years on the active reserve list. The full-time service requirement was reduced to 18 months in October 1971. The Defence Act was amended May 1964 to provide that national servicemen could be obliged to serve overseas, a provision that had been applied only once