A new military agreement signed by Australia and the United States will allow for more US marines and aircraft in the Northern Territory and closer co-operation on missile defence.
The Force Posture Agreement sets out the legal framework for the presence of US marines based in Darwin, now numbering 1150 but set to rise to 2500.
More broadly, it will allow the US to expand military assets over the next 25 years in Australia beyond the troop rotation.
That includes greater co-operation on ballistic missile defence systems, but speculation that US troops could have greater access to a wider number of Australian military bases has been downplayed.
The signing was the centrepiece event at the Australia-US Ministerial Consultations in Sydney on Tuesday, which bring together the defence and foreign ministers of each nation for high-level talks.
There was applause as US Secretary of State John Kerry and Defence Secretary Chuck Hagel put pen to paper alongside their Australian counterparts Foreign Minister Julie Bishop and Defence Minister David Johnston.
The terms of the agreement were reached by Tony Abbott and Barack Obama during the prime minister's visit to Washington in June.
