It is the first time US Army personnel will join the annual Marine Rotational Force deployment in Darwin.

The 2022 force will be comprised of about 2200 servicemen and women based in the Top End during the upcoming dry season.

It is the 11th deployment to Australia and will include 250 US Army personnel, the Australian Defence Force says.

Soldiers trained to use the Patriot Surface-to-Air missile system, High Mobility Artillery Rocket System and unmanned aircraft will be part of the contingent.

The force is part of the ongoing US posture initiative to promote stability in the Indo-Pacific region.

It sits alongside the Enhanced Air Co-operation program between the Royal Australian Air Force and United States Air Force.

About 1000 Marines have already landed in Darwin.

They will train with the ADF to ensure they are able to respond to crises in the region.

That could include humanitarian assistance, disaster relief, evacuation missions, reinforcing US embassies or military operations.

Darwin's location just south of more than a dozen Asian countries and some of the world's busiest shipping lanes makes it a strategic stepping-off point.

The training will include live-fire military exercises to improve interoperability between Australian and the US forces and other regional allies.

Commander of the ADF's northern force Colonel Marcus Constable said the US alliance was Australia's most important defence relationship and central to the nations's security plan.

"The (Marine rotational force) is a key way we increase regional co-operation with partners in the Indo-Pacific," he said.

"Together we conduct a comprehensive range of training activities including humanitarian assistance, security operations and high-end live fire exercises."

USMC commander in Darwin Colonel Christopher Steele said the Marines from southern California were excited to contribute to regional security.

The Marines are expected to complete the rotation in October.

Australian Associated Press