Vietnam is actually a very good example of how true friends and allies should disagree with eachother. The official policy of the U.K. towards the Vietnam War was opposed. The British government (officially at least) did not support the U.S. in that war. However, the U.K. did not in anyway hinder America, or try to rally support against them. In fact, as Yimmy alluded to, behind the scenes the British government did provide some, albeit limited, support... such as the S.A.S. assisting with the training of South Vietnamese troops. This doesn’t make the British government two-faced... what it does is provide an example of how you can object to what an ally is doing, but not seek to discredit or attempt to foil said ally.
A certain European country (that shall remain nameless) would do well to learn from this.
To reiterate what Yimmy said, Australia sending troops to Vietnam doesn't make it a better ally than the U.K., they just so happened to agree with the war whereas Britain did not.
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