The United States is to boost its military activities in Australia under an agreement that will allow America to enhance its presence in the Asia Pacific region.
It will involve joint training and other military exercises, and comes off the back of the US military's review of its global presence.
The deal, announced by US President Barack Obama and Australian Prime Minister Julia Gillard in Canberra on Wednesday night, means that Australia will, by 2016, play host to a US Marine task force of 2500 troops. It will start with 250 soldiers next year.
The agreement will not involve a permanent US military base but US troops for the first time will be given formal approval to train alone.
While Washington appears to be sending a signal to China and its expanding military with its deployment in Australia, the White House also wants to extend its capability to deploy to disaster response missions in South-East Asia.
President Obama says the deal will benefit the whole region.
"We are two Pacific nations, and with my visit to the region, I am making it clear that the United States is stepping up its commitment to the entire Asia Pacific," Mr Obama says. "In this work we're deeply grateful to our alliance with Australia and the leadership role that it plays, as it has been for six decades.
"Our alliance is going to be indispensable to our shared future and the security we need and the prosperity we seek not only in this region but around the world."
President Obama says more US military aircraft will come through Australia and there are plans for more ships and submarines - including nuclear-powered vessels - to move through HMAS Stirling naval base in Western Australia.
Ms Gillard says the agreement will allow America to enhance its presence in the Asia-Pacific region.
She says it will strengthen the alliance between the two countries. "We are a region that is growing economically but stability is important for economic growth too, and our alliance has been a bedrock of stability in our region."
Ms Gillard says the US airforce will also be given more access to Australian bombing ranges and training facilities, in remote areas of the Northern Territory.
Mr Obama smiled and waved as he descended the steps of Air Force One after it landed at the Fairbairn defence establishment in the national capital, Canberra, at the beginning of his two-day visit.
He was greeted by Governor-General Quentin Bryce, Ms Gillard, Australia's ambassador to the US Kim Beazley and US ambassador Jeffrey Bleich.