I’ve long argued that its of little use Australia has SSNs as a China deterrent.
This is if our SSNs are merely armed with torpedoes, Harpoon and/or Tomahawk subsonic SLCMs and mines. These would only add up to a total “throw weight” of 25 tonnes of high explosive, maximum. Land attacking China merely with high explosive, subsonic, SLCMs would result in many/most being shot down, fail to deter China, but just make China more angry.
Australian SSNs need sufficient vertical tube versatility to be armed with hypersonic missiles of various sizes, or even ballistic missiles.
So it is by good fortune that the US SSN(X) debate is publicly leaning (on Nov 10, 2022) towards larger 9,000 tonne Seawolf sized SSNs/SSGNs. The Seawolf Mark I’s beam/diameter is 12m permitting a longer/taller missile than the Virginia’s diameter of 10m.
Hypersonic Missiles on Block V Virginias & SSN(X)/Seawolf Mark IIs
There appear to be plans to deploy Hypersonic Missiles on Block V Virginia SSNs and presumably on not yet diameter designated SSN(X)/Seawolf Mark IIs (but likely of 12m-13m diameter).
Looking at USNI News (Nov 3, 2022) it seems the USN sees it possible that 3 x Common Hypersonic Glide Bodies (C-HGB) and their boosters could fit in each of 4 Virginia Payload Tubes (VPTs) of 2.2m diameter, behind the sail, by 2029. That is 12 x C-HGBs per Virginia, Block V (the first being USS Oklahoma (SSN-802)).
Meanwhile, the 2 VPTs in front of the Block V's sail may not have the versatility/position to be lengthened - so may be still restricted to subsonic Tomahawk SLCMs.
SSN(X)/Seawolf Mark IIs Capable of Taking 4 Trident IIs?
The 2.2m diameter of VPTs originated from the 2.2m diameter of the originally Trident II silos on the 4 Ohio-class that became SSGNs. Those silos were then converted to each take 7 x Tomahawk missiles. The 7 Tomahawk accommodating diameter was then carried over as VPTs to Virginias.
It is highly likely the VPT will be carried over to the SSN(X)/Seawolf Mark II.
So Trident II SLBMs, at 2.11m diameter, can horizontally fit into a 2.2m Virginia Payload Tube (VPT), but not vertically (yet).
But vertically? Where I'm going with this is if a Seawolf Mark I’s hull diameter of 12m is only increased by 1m for an SSN(X)/Seawolf Mark II that would make a diameter of 13m.
13m just happens to be the diameter of an Ohio SSBN and planned 13m diameter of a future Columbia SSBN. These, of course, can/will vertically fit a Trident II’s 13.58m height owing to their slight hump.
This would give SSN(X)/Seawolf Mark IIs of 13m diameter and with 4 VPTs the capability to accommodate 4 x Trident IIs.
This might be a future capability much valued by Australia - if its 8 future SSNs happened to be US SSN(X)/Seawolf Mark IIs. Fear of China has made possible the unprecedented AUKUS SSN offer. Increasing fear of China (say, in 2030) may swing the Australian public in favour of an Australian nuclear deterrent.
If Australia chooses the UK, perhaps UK SSN(R)s might have the same SSN(X) dimensions enabling a Trident II capability.
This thought should not be confused with the nuclear armed Tomahawk TLAM-N debate. Tomahawks, against a nuclear armed enemy, carry with them the "is it carying a conventional or nuclear warhead" ambiguity-misunderstanding. There is no such ambiguity-misunderstanding with SLBMs as they are always assumed to be a nuclear tipped deterrent.