This might just be personal quirk of mine, but I really dislike it when people mention the idea of building additional "Hobarts" as this really is not possible given that some of the systems fitted to the current DDG's are out of production and no longer available. Australia certainly could have a new design with comparable capabilities built, but it would not be the same class of vessel. Some of the systems would be different, and likely the internal layout.
I do not wish to get into the whole pile of issues with the existing
Hobart-class DDG's being space and weight/displacement limited which AFAIK has already impacted what upgrades are planned. Having a new class with a similar role as well as size and displacement would likely run into the same issue, or a related one in that there could be problems fitting available kit of comparable capabilities to those in service aboard the current
Hobart-class, or future kit to be included in their planned upgrades.
There is also the very real issue of what kit would be needed for vessels of a comparable role, what of that kit is available and what kit can Australia already operate and support. IMO this is an area where there is the potential for major stumbling blocks to any new/additional build programmes. Given that the role of the DDG's is air warfare/area air defence and they are fitted with the Aegis CMS and SPY-1 radar arrays, it would be reasonable to believe that a new set of DDG's would also have Aegis CMS and a comparable radar array. If Aegis is a requirement (a reasonable belief for a RAN DDG IMO) this would be a major stumbling block, given the amount of time needed to get them. The US DSCA announced in June 2018
here that Spain had requested to buy five Aegis systems. Given the time frame, these could only have been intended for their F-110 frigate programme the
Bonifaz-class with construction of the lead ship starting in April 2022. I have not been able to determine how much earlier it was that Spain submitted the purchase request but I would not consider it unreasonable for the various US agencies to take a year to determine such a purchase was acceptable. I would also not consider it unreasonable for ship construction to need to have been underway (pardon the pun) for a year before enough of the vessel was completed for the CMS and radars to be fitted, with vessel launch another year or more away.
Working back the timeline for Navantia's ongoing build, it is likely that the design for the
Bonifaz-class had largely been set when Spain likely requested to buy Aegis from the US, and this would have likely been made some time in 2017. Current Spanish plans are for the lead ship to be launched in 2024 and commissioned the following year. So about seven years from DSCA announcement to commissioning and likely eight years after the gov't to gov't buy request for the CMS. Of course, even after the lead ship is commissioned there would need to be various ship trials to make sure the vessel functions as intended and request, before the new ship could be reasonably considered available for ops and deployment. One to two years for builders trials and ship acceptance seems to be fairly normal for large, complex warships like DDG's or FFG's, which would most likely put the first new Spanish frigate available operationally some time in or after 2027, or about a decade after long-lead kit for a specified design was requested.
Applying that same logic chain to more DDG's for the RAN, if a design was already selected now and some of the initial requests were made now, the lead ship would most likely not be available until some time in 2032/2033 and that is also making the assumption that build space in a shipyard somewhere was not an issue. If it is absolutely essential that additional units have to be in RAN service before that time, then Aegis-equipped vessels are pretty much excluded. There is also the potential for a similar sort of situation with the availability of Mk 41 VLS, with a DSCA announcement
here from 2020 including three shipsets of Mk 41 for the
Hunter-class FFG. IIRC it is likely that the lead FFG will be laid down this year, three years after the DSCA announcement covering the VLS for the first batch of frigates.
As much as I would like to see the RAN expanded in size and capabilities, I see little value in getting additional hulls in the water which are not fitted out with systems useful to and able to be maintained by the RAN/Australia. In terms of getting additional, functional vessels into RAN service within the next decade, I suspect the best that could be managed would be a hodge-podge of vessels fitted with whatever was available and being of rather limited utility given the problems that the RAN would likely encounter both maintaining essentially bespoke vessels and systems, but also in getting operators trained on specific systems used no where else in the RAN. One should remember that there is a reason why the RAN decided to adopt the 9LV CMS interface across the fleet, including aboard the AOR's, LHD's and OPV's as well as the FFH, DDG and planned for the FFG.
Just my opinion, but if Australia can manage to weather whatever happens between now and ~2030/2032 AND if there is a real plan and agreement to expand the size of the RAN both in terms of personnel and warships, then there are other approaches which I feel would be more likely to be achieved.
One option would be to start working, now, on plans to have a third class of escort vessel commissioned into the RAN starting just after the
ANZAC-class frigates begin getting decommissioned. What I have in mind would be more like a 2nd tier GP frigate fitted with systems comparable to or perhaps even pulled directly from upgraded
ANZAC-class frigates as they are decommissioned. Given a choice, I would have such a hypothetical class somewhat larger than the current FFH's, probably around the planned size for the USN's
Constellation-class frigates or the RN's Type 31 frigates to leave space and weight for future capabilities and upgrades.
Another option which IMO is also worth consideration is the idea of bring the
Hobart-class DDG replacement forward. Right now the assumption seems to be that the replacement DDG will start construction after the last Hunter-class frigate is completed, with construction being done in Osborne. However, if the Civmec facilities at Henderson are expanded or upgraded sufficiently to enable construction of major warships, it might be possible for Australia to carry out two simultaneous build programmes, one for the Hunter-class FFG's and the other for GP frigates or new/replacement DDG's.
If either idea was started now, selection of a preferred design might be possible by the end of this decade. Following this, orders could start getting placed for some of the long-lead items as well as selection of kit to be pulled from FFH's as they retire, First steel of the lead vessel might be possible by the start of next decade with the first of a new class vessel entering RAN service in the early to mid-2030's.
These ideas would not deliver new capabilities this decade, but I honestly just do not see a viable way for the RAN to get useful capabilities in that time frame. What would be required to be useful is either not realistically available in the timeframe, or unfamiliar to the RAN which would then need time to become familiar enough to make use of what is available. In some cases, I suspect the answer is that kit is neither available or familiar to the RAN and could not be gotten soon enough for RAN personnel to make effective use by the time people believe a major crisis will occur.