Australia runs their own submarines the Collins class. Difference is the new subs will be nuclear powered.
This is a strategic problem, not a tactical one.First, what is the American strategy?
War, the better strategy is to make Australia a military base for the US. The US can put nuclear silos in Australia and build more air bases, naval ports. It is a waste for Australia to spend hundreds of billions of dollars on 12 submarines.
Cold war, the United States should first withdraw gradually from the Chinese market and rebuild its manufacturing industry at home. Australia should join the US-led global industrial chain and perhaps build a large steel industry to supply metals to the US. This would require more infrastructure and buying submarines would still be a waste.
Competition and cooperation, military conflict is unlikely. China still needs 4 billion tons of steel for its iron cycle. Australia has about five years to cushion itself against a sharp fall in demand for iron ore. It's crazy to spend money on submarines at a time when Australia needs to invest upfront for its future economic transformation.
So buying submarines was a completely inexplicable move.
My guess are three possibilities.
The first is that the US is trying to create a sense of threat to China in order to increase its leverage in the sino-US negotiations.
The second is that the US will release the news of providing submarines to Taiwan next, again to increase the leverage.
Third, the US military-industrial complex needs money.