Australia is buying 24 Seahawk combat helicopters at a cost of over $3 billion, Defence Minister Stephen Smith has announced.

The Sikorsky-Lockheed-Martin MH-60R 'Romeo' choppers will replace the existing Seahawk fleet and will come into service over the period 2014 to 2020.

Announcing the purchase, Mr Smith said the US-built Seahawk was chosen ahead of a rival bid from Australian Aerospace, which offered the European-designed NH90 NFH.

"It's a proven capability - it's currently being used by the US Navy. It is the updated version of the Seahawk that we currently use which it is replacing," Mr Smith told reporters at Parliament House.

"It is interoperable with our alliance partner the United States and because of its proven capability it's low risk and we very strongly believe it's value for money."

"This has been through a competitive process - the competitor was Australian Aerospace with the NATO Frigate helicopter, but we have decided to choose the 24 Romeo Seahawks."

Defence Materiel Minister Jason Clare said the Seahawks would be based at HMAS Albatross at Nowra in southern New South Wales.

"They will operate off the back of our Anzac frigates as well as our new air warfare destroyers, and their job is to hunt and kill submarines," he said.

He said they would also be used in anti-piracy and anti-terrorist roles.

"The US Navy has more than 100 of these helicopters. They've flown more than 90,000 hours worth of flying time and they've operated in the Middle East," he said.

Mr Smith said the new choppers would give the Navy the attack capability originally envisaged for the failed Seasprite helicopters.

Australia spent more than $1 billion to bring a fleet of Seasprite helicopters up to operational capability, but the project failed with none of the helicopters seeing service.

Mr Clare said Defence would also be buying another 101 Bushmaster armoured vehicles similar to those used by Australian forces in Afghanistan.

"It's a matter of record that they've saved dozens of Australian lives in Afghanistan, and the purchase of an extra 101 Bushmasters is very important to deal with the attrition of Bushmasters that have been attacked and, in some cases, blown up in theatre," he said.