At the start of the 1960s , Prime Minister Robert Menzies greatly expanded the Australian military so that it could carry out the Government 's policy of " Forward Defence " in South East Asia . In 1964 , Menzies announced a large increase in defence spending . The strength of the Australian Army would be increased by 50 % over three years from 22 @,@ 000 to 33 @,@ 000 ; providing a full three @-@ brigade division with nine battalions . The RAAF and RAN would also both be increased by 25 % . In 1964 , conscription or National Service was re @-@ introduced under the National Service Act , for selected 20 @-@ year @-@ olds based on date of birth , for a period of two years ' continuous full @-@ time service ( the previous scheme having been suspended in 1959 ) .