All nuclear-powered submarines Australia will receive under the AUKUS military pact will be second-hand, Defence Minister Richard Marles has revealed.Australia had been expecting to receive two used submarines and one new one but now plans for all three to be in-service vessels from the United States Navy.Speaking at a high-level gathering of military and defence leaders in Singapore on Sunday, Marles said the new approach would be "cost-effective" and "streamline" the delivery of the Virginia-class submarines.It comes after US defence secretary Pete Hegseth told SBS News that the country is "grateful" for Australian support while warning that other allies need to step up their military spending as he outlined the US' vision for Indo-Pacific security.In a joint statement with his US and UK counterparts, Marles said the "seabed is a battlefield" as he announced a shift in focus from pillar one of the AUKUS deal to pillar two One of the biggest announcements to come from the conference is the news that Australia will only receive old US submarines instead of a newly manufactured one in the first round of AUKUS deliveries