The USS Colorado, a 10-year-old Virginia-class submarine, will make its new home at Western Australia's HMAS Stirling as part of its official rotation from late 2027, Defence Minister Richard Marles revealed in a joint statement with his US and British counterparts on Tuesday.
The submarine arrived early at the WA base on Tuesday, to allow Australian crews to gain skills maintaining the nuclear vessel.
It is the latest vessel to be used as part of the US Submarine Maintenance Period, which aims to ramp up efforts for AUKUS before the vessels start official work.
Six submarines have visited HMAS Stirling as part of the program, with the Colorado the third to undergo maintenance in the past 12 months.
But Colorado's arrival in Australia will be controversial because of outrage sparked in June over revelations the US would deliver lesser equipment than first promised.
Original AUKUS plans had Canberra receiving two used vessels and a brand new Virginia-class submarine before building one of its own in Adelaide.
The fact Washington would now send second-hand vessels was described as "trash" by Tasmanian independent senator and army veteran Jacqui Lambie.
But ministers and top military brass at the time insisted used subs were the best option.
Prime Minister Anthony Albanese at the time assured the public AUKUS was going "full-steam ahead" despite tweaks to the mega-money deal, which US Secretary of War Pete Hegseth reiterated on Tuesday along with Mr Marles and UK Secretary of State Wes Streeting.
Colorado is a "fast-attack" submarine, reaching more than 46km/h, compared to Australia Collins-class subs' underwater top speed of 37km/h.
While second-hand, the Virginia class is Washington's most advanced line of attack submersibles.
The higher-speed, longer-range vessels are needed to help Australia defend its sea trade, Mr Marles has said.
"The selection of USS Colorado ... is a decisive step in strengthening collective deterrence in the Pacific," the joint statement read.
Mr Marles will come face-to-face with Mr Hegseth on Wednesday and Thursday at the ASEAN Defence Ministers' Meeting in the Philippines.
"ASEAN sits at the core of Australia's vision for a peaceful, stable and prosperous region, where all countries are free to exercise their sovereignty," Mr Marles said.
"I welcome the opportunity to deepen defence relationships with some of Australia's key partners in the region."
Australia's nuclear subs will be conventionally armed, but the US has maintained a policy of ambiguity about whether assets rotating through the country are carrying nuclear weapons.
Being nuclear-powered means its range is effectively limited only by its crew's need for food and water.
Tuesday's statement says the AUKUS rotation arrangement will abide with all relevant non-proliferation treaties.
Greens leader David Shoebridge said the presence of US nuclear submarines in WA would put Perth at risk from attack.
"This is not making us safe. This is making us a target in whatever erratic decision this or a future US president will make about war," he told reporters in Canberra.
"This is proof positive we need to end AUKUS."
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