An interesting set of problems. We can barely crew 4 subs (we have 6). Oh wait; one of them is in such a mess it will probably never go to sea again. And some want us to buy 12 subs; large ones that need big crews.
Yet there are subs out there that only take 27 crew and can defend and attack in the littorals to the North.
But I digress. The most important goal of the Collins-class replacement program is that it becomes a jobs program via an iron-lung government run (or run into the ground) project.
Any attempt to defend the country (as a goal) is secondary.