The U.S. Navy has ordered two more join high speed vessels (JHSV) or catamaran worth $321.7 million from Australian shipbuilder Austal. With the two new orders, the total catamaran orders awarded to Austal has reached $1.45 billion.

Austal Chief Executive Andrew Bellamy said the new orders are substantial and would provide predictable revenue and workload for the firm.

In ordering its eighth and ninth catamarans, the U.S. Navy exercised its contract options with Austal.

The joint high speed vessels are 100 metres long with aluminium hull. It could accommodate up to 300 people and vehicles at a speed of over 40 knots to a range of 1,500 kilometres.

The two new orders would be manufactured at the Austal shipyard in Mobile, Alabama. The U.S. Navy initialed awarded the contract for construction to Austal in November 2008, which included options for nine more vessels between 2009 and 2013. Austal stands to earn up to $1.6 billion under the 10-ship programme.

The first vessel, named U.S.N.S. Spearhead, is scheduled for builder sea trials in March, while the second ship, Choctaw County, is under construction. The modules for the third vessel are underway.

Mr Bellamy said that the additional orders indicate the U.S. Navy's confidence in Austal and its products.

"That provides us with significant marketing leverage with which to grow our international defence business in ships, systems and support," he said in a statement.

"This enables us to plan our production approach to deliver high quality, affordable ships in the most efficient way possible and to make and implement medium and long-term strategies," Mr Bellamy added.

Although Australia lacks a catamaran in service, the country pioneered the use of joint high speed vessels when it used a leased catamaran between 1999 and 2001 to transport Australian troops from Darwin to East Timor during the peak of military operations. The vessel was built by Incat, a shipbuilding firm based in Tasmania.

The creation of the JHSV program is the result of the U.S. Navy and U.S. Marine Corps holding their own trials after they used leased catamarans from Austal and Incat.