The following are my first guess-timates of how an Australian nuke sub (which I dub the "Numbat class *)
Thanks Anonymous for your September 24, 2021 comment with some details I provided to you, offline, a few days ago ;-)
The US Contribution - Virginias (maybe)
Yes out to 2043 the US is committed to building around 2 Virginia SSNs per year. The US is also commencing 1 of 12 Columbia class SSBNs per year (as of last year, 2020) all for the USN. On the whole the US wants to build SSNs and SSBNs for the USN as quickly as possible to keep up with Chinese and Russian builds.
If Aus guaranteed that its Numbat (Virginia) SSNs would closely interoperate with the USN then the US may practice some flexibility (for a price) in perhaps doing the Numbat builds in the US and much less likely in Australia. All Numbats might be built in the US for long established US commercial and government security reasons.
The US has been already providing its nuclear submarine Combat (Tactical Control) System (known as the AN/BYG-1) to the Collins class. "The AN/BYG-1 is installed on the U.S. Navy’s Los Angeles, Seawolf, Virginia, SSGN, SSBN and the upcoming Columbia SSBN class, as well as on the Royal Australian Navy’s Collins-class submarines." The US will almost certainly provide that system for Aus Numbats. A combat system consists of sensors, computer hardware and software (for data fusion and targeting) and weapons (likely to remain the US Mark 48 torpedoes, US Harpoon ASMs and (new for the Numbats) US Tomahawk ASM/Land Attack missiles.
Australia and the US have also been cooperating on several longer range and/or hypersonic missile projects (future nuclear capable possible).
The Tomahawks can be fired horizontally through US and UK torpedo tubes. In the Virginia Block IIIs and IVs there are also 2 vertical launch Virginia Payload Tubes (VPTs) with 6 x Tomahawks in each (for a total of 12 vertically fired Tomahawks or a number of newer missiles).
The US may be unwilling to offer its latest, highest tech, submarines to Australia. These would be:
- the much larger more expensive Virginia Block Vs (with likely provision for 28 to 36 vertically and horizontally fired Tomahawk ASM/Land Attack missiles)
and
- the US SSN(X). Likely much more expensive than Block Vs and of course higher tech. If the USN Submarine Service has its way SSN(Xs) are like to be a development of the ASW specialized Seawolfs.
The US would also need to provide permission for Australia to use US designed reactors (which use 90+% weapons' grade HEU) which are, in modified form, also used in UK nuclear subs.
On Monday UK Astute Mark 2s (more likely).
* Budding SSN-zoologists please note. The Australian Numbat is a gentle creature, rarely seen, but if you are a termite watch out, for a Numbat has sharp claws, weathered gums, but a long tongue for sustenance and pleasure. I would have liked to say it Eats, Roots and Leaves, but as this is a PG website I cannot comment on submariner shore leave habits.