AUKUS sub sale under scrutiny as Trump tariffs rattle Australia

"If you want to deter conflict, in peacetime you need to talk about using it in wartime and we haven’t seen a willingness yet on the part of the Australians, government or officials, to make that kind of threat," said former US Navy strategist Bryan Clark, director of the Center for Defense Concepts and Technology at the Hudson Institute, who is advising the Australian Defence Force on force design.

In a previously unreported recent multilateral war game simulating a response by US allies to a Chinese blockade of Taiwan, Australian Defence Force commanders did not use nuclear-powered submarines in the South China Sea to attack Chinese targets, instead focusing on protecting Australia's northern approaches with airpower, drones and missiles, said Clark, who ran the exercise.

The distance from China made an airpower and surface fleet approach less risky, and the submarines were instead placed in areas near Australia where enemy ships might transit, Clark said in an online briefing.

These concerns were echoed in a US Congressional Budget Office report in February and testimony on navy shipbuilding delays in March, in which officials said selling Virginia-class subs out of the fleet to Australia without replacements was risky because Canberra had not made it clear whether its military would join the US in a conflict over Taiwan.