The United States is sending 1,150 Marines to Australia in April, bolstering the roughly 200-member force already in Darwin.
The reinforcements are part of a planned deployment of up to 2,500 US Marines in Australia by 2016-2017, as Washington pursues a strategic "rebalance" to the Asia-Pacific.
Most of the Marines will come from the 1st Battalion, 5th Marine Regiment at Camp Pendleton in California and are "expected to arrive in Australia in early April", the Marine Corps said in a statement.
The force will include four CH-53E Sea Stallion helicopters and about 100 personnel to operate and maintain the aircraft, it said.
"These deployments are a tangible demonstration of the United States' sustained commitment to the US-Australia alliance and to the Asia-Pacific region," said spokesman Colonel Brad Bartelt.
"They enhance security co-operation, disaster response capabilities, interoperability and enable us to train with our partners to develop and maintain our readiness," he said.
President Barack Obama announced the rotational deployment of Marines to Darwin in 2011, a move that has caused irritation in Beijing.
US officials have stressed no permanent American base is being set up in Australia and that the Marines will rotate into Darwin for roughly six-month stints.
In November 2012, Australian and US officials unveiled plans for the American military to station a powerful radar and space telescope in Australia.
Concerned over China's growing military might and assertive stance over territorial claims in the Pacific, Washington has sought to step up its military engagement across the region and bolster defence ties in Southeast Asia.
