Actually Swerve the DDHs are intended primarily to sanitize the waters around Japan, in conjunction with the submarine and MPA capabilities, to provide the USN carrier battle groups with a safe area from where to conduct offensive operations. They also have secondary HADR and, particularly in the case of the Izumos, amphibious capabilities.
Japan builds great subs and without a doubt their current and planned designs are closer to Australian needs than anything else out there, but, unless the Australian government has contracted a case of the stupids, they are most definitely not a MOTS solution for the RAN. What ever design is chosen, it will require extensive work just to ensure it is actually able to operate efficiently in the RANs areas operations and can be affordably maintained through their service lives. The shear idiocy of reports that the boats can be built in Japan (or anywhere else for that matter) and outfitted in Australia, or that the combat systems can be integrated locally shows a total lack of understanding of how submarines are actually built. All equipment and systems are tested, installed on the rafts, that become the submarines decks, that are then slid into the fabricated hull sections which are then welded together, sealing the hull. Combat systems and other major items can be updated or even replaced after the hull is consolidated but this is incredibly difficult, not to mention expensive and time consuming. Such work requires the hull to be cut open, or the systems themselves to be broken down into components small enough to fit through the largest hull opening in an intricately planned process of teams working in and around each other in severely restricted spaces. I call BS on the suggestion that outfit or combat system integration will be done locally on overseas built hulls, the suggestion is either made in ignorance or is a deliberate attempt to mislead the public over the true intent to send all work offshore and dispense with local capability altogether.
Also ASC did a superb job fabricating and maintaining the hulls of the Collins class, the problem was with the quality of some of the installed systems and some design features. This includes some MOTS items that were perfectly satisfactory in other boats in service with other navies but struggled in the RANs area of operations. Over their service lives, many of these systems have been replaced by new improved designs developed by ASC and DSTO in conjunction variously with USN, DARPA, RN, EB and specialist suppliers. Basically ASC have had to graduate from building to print to designer to address the multitude of unanticipated issues encountered during the project.
The Oberons were a conventional fleet submarine designed for global operations, as were the US Tangs and Barbels, but none since, other than the Collins. This is why it is so difficult to find submarines suitable for the RAN, they need to be extensively redesigned to become fleet submarines. This is why any design, even one as good as the Soryu, will need to be modified to the point that it is most definitely is no longer MOTS solution. Anyone who sees the Japanese option, even with a full Japanese design and build, as a risk free MOTS solution is kidding themselves. The take home from the AWD should have been that the supposedly cheaper, easier MOTS option usually isn't and the main effect of outsourcing design authority is when things inevitably go wrong there is limited, if any, local capability to recover the situation.
