Two important anniversaries pertaining to the war of Viet Nam will be celebrated this week. 40 years ago, Australia entered the war and, 30 years ago, Saigon fell into the hands of the north-Vietnamese forces.
_ Later 1964 and early 1965, the debate about the interference in Viet Nam was at its height in Washington. Since the mid 50’s, the United States had military advisors in South Viet Nam, but not ground troops. The debate continued and Johnson’s advisors failed to understand that North Viet Nam could not be defeated with the type of war that the United States could wage. While the debate was going on in Washington, it was decided in Canberra to push the United States to get involved in the war, and Australia sent a battalion to fight in Viet Nam even before the Americans requested so. The Australian diplomacy also pushed the United States to increase the bombardments in North Viet Nam.
_ Australia’s objective was to strongly link ANZUS to be able to have support in case of a conflict with Indonesia. Contrary to what is stated today, the war was not unpopular. In the United States, the politicians who decided this war lost their prestige, whereas our leaders later held high offices. For the United States, that war determined the way to wage the next ones. For the Australians, the opportunities to obtain something from the United States were at stake.

Source
The Age (Australia)

The war we gatecrashed”, by Michael Sexton, The Age, April 28, 2005.