Australia can't avoid the long voyages, because Australia is surrounded by large water areas, that require a lot of travel time to traverse. It is boring to transit all of that distance, and that was exactly what the dispirited sailors reported when asked. At the moment, there is no solution in sight. So while Australia can buy modern submarines, they have not yet found a way to obtain crews to operate the boats.
I don't mean to sound too dense, but isn't the obvious solution to stop making their sub crews make the boring transit? I mean, if that's really the source of the retention problem, stop doing it.
Why can't the Australians load a submarine into a floating dry dock, tow the sub to the general region of the training area, and then fly the crews in to actually carry out interesting training on station? Study the issue of when boredom creeps in and then make sure that this part of the at-sea training doesn't exceed what submariners can handle and want to reenlist. This obviously isn't a wartime practice, but once war breaks out, retention becomes a non-issue.
Couldn't the Australians rotate crews through peacetime training like this, and also use on-shore simulations to bolster the skill of transit (and other more interesting aspects of training)? With 12 new subs the goal, you might have 2 on actual patrol with a couple more on training duty towed to wherever the training is to take place, supported by tenders and perhaps small floating bases (based on container ships?) for supporting personnel and facilities. Crews could rotate into these training boats and the remaning 8 would provide rotation boats for the patrol and training stations, with some not undergoing extensive maintenance able to surge in emergencies. With perhaps 24 crews for 12 boats, ideally, the actual patrol assignments that require long transit times would be spread out and lessen the effects of boredom on retention.
I'm not sure if I'm being obvious or oblivious on this matter, but isn't it better than having only 1 out of 6 subs ready for action because of lack of crews and maintenance?
With 12 new subs planned for defending Australia, something has to change if the Australians want availability better than 1 or 2 out of 12, and it isn't going to be crew toleration for boring transit duty that changes.