Australia was formally allied with the United States by both the SEATO pact of 1954 and the ANZUS treaty of 1951. Both were designed to contain the spread of communism in SE Asia and the Pacific. In 1962 the government of South Vietnam, though not a signatory to either treaty, requested military assistance to combat a communist threat from both internal and external forces. The USA, which had been providing lower level assistance since the mid 50s, had 11,000 military "advisors" in Vietnam by the end of 1962. The Australians deployed 30 advisors that year as part of their treaty obligations with the USA. The Menzies government in 1965 decided to increase their commitment to the war and eventually Australia committed 7,600 troops at it's high point. 60 thousand Australians served in the war, including significant air and ground troops. The "domino theory" of spreading communism was widely held in the Australian government during the early years of their involvement. Like the USA the Australians had a military draft and like the USA the war became increasingly unpopular at home. Michael Caulfields, "The Vietnam Years: From the Jungle to the Australian Suburbs" is a readable source.