I understand what Peter Briggs is saying but beg to suggest that it is fantasy dressed up as strategy. Australia has one of the longest coastlines of any country on the planet. We also have a miniscule population compared to any likely adversary. We are also many thousands of kilometres from much of the world.
That means a herculean task that any tiny fleet of our nuclear submarines is required to address. The suggestion that whatever we can afford, and that in itself is an unresolved question, would have any deterrence of any consequence to a major power borders on the absurd.
Even if we could afford a fleet of 6 to 8 nuclear subs what we know about their availability would suggest that at most 2 would be available at any time to cover the millions of square miles of ocean surrounding us. What their usefulness would be against an opponent with many multiples of our financial and shipbuilding capacities, who could saturate the oceans surrounding our two submarines, can only be imagined.
Instead let us defer to Sun Tzu and Machiavelli in developing our diplomatic skills rather than wasting vast sums of our national wealth!!