On 4 Mar 2023 the Australian government announced
a plan to acquire three US Virginia class nuclear-powered submarines from 2030, with modified UK Astute "AUKUS" class submarines built in Australia from 2040. If there are delays with the AUKUS class, Australia has the option to purchase another two Virginia class submarines from the USA. However, I suggest the Australian government have a third option ("Plan C"): accelerate the development of drones, to arm the submarines and operate alongside them. If the drones prove successful, Australia could stop acquisition at three Virginia class, not purchase any more crewed submarines, and not build any.
The largest of the drones would be ocean going robot submarines, capable of conducting surveillance, launching weapons, and perhaps even carrying small raiding parties. The robot submarines would be small enough to be transported by cargo aircraft, and could be maintained from, and carried on Australian made high speed transport ships.
The smaller drones would be the size of mini, lightweight, and full size torpedos. Some drones would operate as smart mines, then attack as torpedos. Others would provide aerial surveillance, and attack. These drones could be launched from submarines, ships, and aircraft.