The Australian military plans a fleet of eight P-8As to replace its ageing AP-3C Orion fleet.
Implementation of the advance acquisition contract will give Boeing time to place lead-time orders for components in support of Australia's first four P-8As.
"Together with high altitude unmanned aerial vehicles, these aircraft will replace the Royal Australian Air Force AP-3C Orions that have served Australia so well for over four decades," said Minister for Defense David Johnston. "These state-of-the-art aircraft will dramatically boost Australia's ability to monitor its maritime approaches."
He said the P-8A could also conduct search and rescue, anti-submarine and maritime strike missions using torpedoes and harpoon missiles.
The P-8A is a multi-mission maritime patrol aircraft with an airframe based on Boeing's 737-800ERX commercial jet. It was introduced into service last year. It has a range of 1,200 nautical miles and a cruise speed of 440 knots.
The first Poseidon is scheduled for delivery to Australia in 2017, with all remaining aircraft delivered by the following year.