Australia's first nuclear-powered submarines could be in the water before 2040 under a historic partnership with the United States and United Kingdom.
A $90 billion deal with French company Naval Group has been torpedoed, with Australia switching to at least eight more-expensive boats using nuclear propulsion.
Prime Minister Scott Morrison hailed the new AUKUS pact as a "forever partnership" which would be the most important alliance since the 70-year-old ANZUS treaty.
Defence spending will be increased to fund the submarines and boost Australia's long-range strike capability including Hawk and Tomahawk cruise missiles.
The nuclear submarines with unlimited range will not require reactors in Australia, with sealed modules for the vessels to be sent from the UK or US.
They do not require refuelling, with the nuclear system lasting the life of the submarines which are faster, have greater stealth and more carrying capacity than conventional boats.
An 18-month consultation period will determine workforce and training requirements, production timelines and safeguards on nuclear non-proliferation agreements.
Construction is expected to start before the end of this decade.
Australia will become the first nation without nuclear weapons to acquire the submarines.
Mr Morrison said no civil nuclear capability would be needed in Australia.
"This is not about acquiring nuclear weapons," he told reporters in Canberra on Thursday.
"Australia has no interest in that. No plans for it, no policy for it, no contemplation of it. It's not on our agenda."
Mr Morrison confirmed Australia spent $2.4 billion on the scrapped French submarine deal for 12 Attack-class submarines.
"Of course they're disappointed," he said.
He stressed the decision did not reflect on the Attack class, Naval Group or the French government.
"If we were unable to access this technology to have a fleet of nuclear-powered submarines, then the Attack-class submarine is the best conventional submarine," he said.
South Australia has secured the maintenance and upgrade - known as full-cycle docking - of Australia's fleet of Collins-class submarines beyond 2026.
UK Prime Minister Boris Johnson said the AUKUS pact aimed to preserve peace and stability in the Indo-Pacific region.
"We're opening a new chapter in our friendship," he said.
"The first task of this partnership will be to help Australia acquire a fleet of nuclear-powered submarines."
US President Joe Biden said it was a historic step to deepen co-operation between the three nations.
"We all recognise the imperative of ensuring peace and stability in the Indo-Pacific over the long-term," he said.
China's Washington embassy spokesman Liu Pengyu said countries should not build exclusionary blocs targeting or harming the interests of third parties.
"In particular, they should shake off their Cold War mentality and ideological prejudice," he said.
Mr Morrison is due to travel to Washington next week for a meeting of the Quad alliance of the US, India, Japan and Australia.
It will be his first US visit since Mr Biden became president.
Defence Minister Peter Dutton and Foreign Affairs Minister Marise Payne are already in Washington for the 31st annual Australia-US Ministerial Consultations, or AUSMIN.
with Reuters
