$40 billion submarine project , page-17

bacci.
"If we want subs buy Virginia class nuclear subs from the Yanks. They have spent billions perfecting them"

Exactly,
And with nuclear we have no worries about refuelling. They can travel all over the world for many years. Conventional is hopeless with Australia being such huge distances from potential action areas. The latest US aircraft carrier is permanently at sea and will need refuelling in 22 years.