Mini-subs. Every Coastal town should have one.
Considering we have the German & Nipponese 'mini-subs' as a successful precedence from WW2.
Why Australia can't build upon that - I don't know?
By having a school of Mini-Subs around the Continent, the enemy would not be able to make a successful 'landfall' to mount an engagement with 'Tanks'.
The only help they could do 'in advance' would be a mobile coastal gun shooting short range out at sea, besides long range traditional Artillery.
And if the USA can make 'Carriers' for Jet Fighters for the Sky.
Why can't Australia make 'Carriers' for Mini-Subs, beneath the waves?
Maybe the Australian Government thinks the 'Sharks' will protect Australia?