Here’s a study from CACDA about the AUKUS subs project. Here’s an excerpt concerning an Australian nuclear weapons program:

In 1967, then Prime Minister Holt and the Defense Council of Australia arranged a research program to assess the possibility of Australia to manufacture nuclear weapons independently and the arrangements with its allies. In January 1968, new Prime Minister Gorton explicitly refused to sign the NPT, and at the same time launched an ambitious nuclear weapons program that included spending on building nuclear reactors and uranium enrichment plants, producing weapons-grade plutonium and weapons-grade HEU for nuclear warheads, and strengthening its nuclear research talent pool. The then Australian Foreign Minister McMahon supported joining the NPT and pressured Prime Minister Gorton through the UK and the US. Australia finally approved the NPT in January 1973, and since then Australia’s status as a non-nuclear-weapon state was formally fixed in legal form.