Scomo just turned Australia in a superpower :) EPIC!, page-84

Being initially armed with conventional weapons doesn't mean that nuclear weapons cannot be carried if the threat should require it. So if a belligerent nation should threaten the Australian mainland with a ballistic missile strike, it could be assured that the potential does exist for a mobile and almost undetectable platform to launch a devastating retaliatory strike. And Australia can do so without having to invest in a land based ballistic missile shield and vulnerable land based deterrent ballistic missile technology. So it might be better for any such belligerent nation to to decide against empire building and consider more peaceful ways to get along with the world than wasting money on a military buildup to threaten it's neighbours.