The order is Austal's second for EPFs in this financial year, which the company said will lead to full vessel contracts later in the fiscal year.
Long lead-time materials for the additional vessel will include diesel engines, water jets and reduction gears.
The Australia-based company have been tasked with building 14 vessels of the class for the US Navy, after receiving its first contract for a 103-metre EPF in 2008.
In the past decade, 10 of those vessels have been delivered, with three currently under construction.
The EPF is an aluminium, shallow draft catamaran that has the capability of intra theater personnel and cargo lift, which offers high-speed sealift mobility.
The class is designed to transport 600 tonnes of military cargo up to 1,200 nautical miles at a speed of 35 knots, and is designed to operate in areas too shallow or narrow for larger ships in the US Navy fleet.