Part of SEATO (Southeast Asia Treaty Organization) & ANZUS (Australia New Zealand United States treaty).
The same as with the US, normal relations.
They followed the US's lead. What the US did, Australia did.
Relationships between Australia and Vietnam are generally along the same lines as the relationship between the US and Vietnam.
It mirrors US relations.
Mirrored US.
Yes, Australia fought in the Vietnam war on the side of the capitalists. They joined the war as a coalition with the US as a proxy war of the Cold War, and fought against the Vietcong and communists in an effort to prevent the Domino effect, an ideological security issue. Furthermore, Australia joined to retain the special Great and Powerful Friends relationship it has with the US in its usual sychophantic manner.
Australia was an ally of the US and sent troops to fight in both WWII and Vietnam.
Australia mirrored US actions.
US, Australia, Thailand, S. Korea, S. Vietnam, Philippines, New Zealand.
New Zealand, US, South Korea, South Vietnam, Philippines, Thailand.
They mirrored the US; protests, etc.
Like the US, the last time was the Vietnam War.