Regarding matters raised by Bill Seney in his comments of 15 March 2025, I respond:
The Port of Darwin is a poor choice for even temporary porting (say one month) of a Collins submarine, let alone large SSNs. This is due to its tidal changes (very shallow water a couple of times a day) and consequent inability of a small Collins to leave port for part of the day and/or reliance on creeping through very narrow channels.So large US submarine tenders (like the 23,000 tonne Emory S. Land class) are not suited to Darwin's inner harbour. Rather the outer harbour is deep enough for such a tender and for SSNs.
Emory-class tenders are used at US Middle East naval bases (often merely called "wharfs"), the Diego Garcia base, occasionally at HMAS Stirling, but mostly at the US Apra-Guam naval base.
Things may be different for much smaller depot ships used by other countries, like the UK, which are scaled down for small-moderate defence budgets.
Twofold Bay?
If Australia had its own small depot ship an appropriate East Coast deepwater port it could use is underpopulated, uncrowded, Twofold Bay, just south of Eden, NSW. There is already a tiny RAN facility there, which Collins submarines and other RAN warships occasionally use.
Twofold Bay is midway between Melbourne and Sydney and doesn't suffer from the incumbent high shipping use or population overcrowding of the other three east coast sites considered for an east coast SSN base. There may be ample room to eventually build a 300,000 population city in that area, called the Far South Coast of NSW.
Australia's broader submarine tender/depot discussion frequently extends to depot ships in Australia's Christmas or Cocos Island territories. To that I say submarine depot ships and ported subs are valuable assets that must be defended by near co-located friendly warships and fighter aircraft mostly against Chinese attack.
French SSNs for Australia?
Re part building French SSNs in Adelaide - Australia would have much to do regaining French trust and offering big money to France. AUKUS Pillar One would need to be stone dead FIRST beforehand. US intelligence would know straightaway if we were chatting to the French.
Australia cannot really afford AUKUS let alone courting a simultaneous French SSN deal.
Also its bad timing. France has got its hands full being the alternate nuclear defender of NATO ever since US "diplomacy" became a Russian plaything.
It takes decades to develop an efficient, discrete submarine "reactor package". Even the UK didn't attempt it - instead buying a US S5W reactor for the UK's first nuclear sub and heavily relying on US reactor tech ever since.
100kt warheads for SLBMs are the world standard minimum. Perhaps that would also apply to future Australian submarine launched hypersonic missiles. So yes "boosted fission" or even better 2 stage thermonuclear is the go.
Buying from Israel might cut corners. But don't tell anyone I thought it up! H-Bomb negotiations are a tad sensitive...