The Australian Government is considering a Collins class submarine replacement. Twelve larger, longer range vessels are proposed, which can carry special forces and deliver strategic weapons on land. This is overly ambitious, given that currently only one of the six Collins class submarines is operational. The greater complexity of the proposed replacement the project has minimal of success and it is unlikely that any of the twelve submarines would become operational, if they were built.
An alternative approach would be to prioritise what is required and build simpler, smaller vessels. The primary mission of the submarines is surveillance, secondary is to attack shipping. Accommodation of special forces can be done by providing dual purpose space which can be used for storage or people on a particular mission. Strategic attack of land targets using missiles is not a priority.
Assuming the current Collins class submarines could be made reliable, their capacity to carry special forces and their range could be increased by reducing the weapons systems and loads. Halving the number of torpedo tubes and halving the maximum load of weapons would free up about 50m3 of space, for more supplies or special forces. Using precision guided weapons, less should be needed for any mission.
However, problems would remain with the Collins class. A better alternative would be to build a proven design, with the minimum of modifications. As an example, the German Type 214 submarine is built in several countries. It has a crew of half the Collins class. The 214 design could have half its torpedo tubes and half the weapons storage removed to add more room for stores. The submarine could be lengthened by 6m to add more room. The speed would be reduced, but that is acceptable given the primary mission of the submarine is surveillance.
In addition Australian designed and built Joint High Speed Vessels could resupply the submarines in friendly ports or at sea. The US Defence Department has confirmed it will order two more of these vessels. A fleet of twelve type 214 submarines and six JHSVs to support them would cost less and use a smaller crew than twelve improved Collins class vessels, be faster to bring into service and more likely to actually work.