The 331-foot WestPac Express, used by the U.S. Marines' Third Marine Expeditionary Force, is for rapid deployment of troops and equipment in the Western Pacific.
The extension is for a period of six months -- to February of next year. The cost for extending the charter was not disclosed. The charter includes in-service support, ship management services and integrated logistics support.
The catamaran can carry as many as 900 Marines and as much as 550 tons of vehicles and equipment and can reach a speed of as much as 36 knots.
Austal is the prime contractor to the U.S. Navy for a $3.5 billion contract to build 10 Independence-variant Littoral Combat Ships and a separate $1.6 billion contract to build 10 Joint High Speed Vessels.
Austal said the extension of the charter for the catamaran comes 12 years after Austal first contracted the high-speed catamaran with the Navy.