"The optimistic assumptions that guided defence planning after the end of the Cold War are long gone," said Defence Minister Richard Marles, unveiling a gloomy assessment of regional security and the risk of war.

Warning "China has employed coercive tactics in pursuit of its strategic objectives," Marles said "Australia no longer has the luxury of a 10-year window of strategic warning time for conflict".

Instead of focusing on a balanced military that can do a range of tasks almost anywhere in the world, Marles said there would be a laser focus on protecting Australia's interests in its immediate region.

"We are a maritime trading island nation," Marles said, adding that Australia must be able to prevent foes from strangling trade or preventing access to vital shipping lanes.

"The invasion of Australia is an unlikely prospect in any scenario, precisely because so much damage can be done to our country by an adversary without ever having to step foot on Australian soil," he said.

At the centre of the strategy is developing a fleet of stealthy nuclear-powered submarines, tripling key missile capabilities and developing a large surface combatant fleet.

"Having the most capable Navy in our history will be at the heart of our projection and our strategy of denial," Marles said.