Australia announced last week that it had finalised a Aus$50 billion ($35 billion) deal to buy 12 attack-class submarines from the Naval Group consortium, partly owned by the French state.

The contract had been under discussion for years -- a preliminary deal was signed in 2016 -- but the final signature capped a period of intense diplomatic activity propelled by French President Emmanuel Macron.

"France and Australia have entered a completely new phase. We've never been this close," Australia's ambassador to France, Brendan Berne, told AFP.

"It's more than a contract; it's a partnership based on trust. Through this project the French are entrusting us with key elements of sovereignty."

Although ties between Paris and Canberra were improving even before Macron's election in 2017, Berne said the 41-year-old leader "sees Australia through new eyes".

Macron made his first official visit to Australia in May last year, when he proposed strengthening the axis of democracies between India, Australia and France in what was billed as a major foreign policy speech.

Underpinning the relationship is a concern about the future of the Indo-Pacific region which stretches from the east coast of Africa to the west coast of the Americas, and includes the disputed territories of the East and South China Seas.

As Admiral Phil Davidson, commander of the US Indo-Pacific Command, said in January during a speech in India, "the future for prosperity -- not only for the United States, but all nations of the region -- is resident in the Indo-Pacific."

It hosts vital international trade routes and abundant natural resources, which many nations have an interest in claiming -- above all regional superpower China.

- Setting a precedent -

France has a major stake through its colonial-era Pacific territories -- French Polynesia, New Caledonia, Reunion, Mayotte, and Wallis and Futuna -- which are home to more than 1.6 million citizens.

Because of the scattered territories, France possesses the world's largest Exclusive Economic Zone (EZZ) of nearly nine million square kilometres (3.5 million square miles).

As Berne points out, France's biggest maritime border in the world is with Australia, and the capital of New Caledonia can be reached by just a two-hour flight from Brisbane.

Both nations have also been alarmed by increased Chinese assertiveness, particularly in the South China Sea, where Beijing is building up its military presence in a bid to claim the strategic seaway as its own, analysts say.

"For France, because it has the largest Exclusive Economic Zone in the world, respect for the law of the sea isn't an abstract concept," said Philippe Errera, an advisor at the French foreign ministry.

"If the law of the sea is not respected today in the China Sea, it will be threatened tomorrow in the Arctic, in the Mediterranean Sea and in the Indian Ocean," he said.

Apart from Australia and India, France has also been trying to beef up ties with Malaysia and Singapore, and plans to soon deploy its aircraft carrier, the Charles de Gaulle, to the Indian Ocean.

- High stakes -

For Australia, France's renewed interest in the region under Macron is welcome support at a time when US commitment to the region under President Donald Trump is increasingly questioned.

"China is the biggest challenge for Australian foreign policy," Michael Fullilove, executive director of the Lowy Institute, an Australian foreign policy think tank, said at a recent conference in Paris.

"How do we give a strong message to China -- we know China doesn't respect weakness -- without ruining a relation that is unavoidable, forever?" he asked.

Australia and France, he said, are "beneficiaries of a rules-based order" which together they can try to uphold.

Australia is also reassessing its relationships in Europe in light of Britain's decision to leave the European Union.

London's tortuous negotiations to leave the bloc have sapped its diplomatic energies, while Britain increasingly lacks the defence manufacturing capabilities that France has retained.

"The UK has lowered its international ambitions," said Fullilove, adding that "France is a global power with global power-projection capacity."

Maaike Okano-Heijmans, a senior research fellow at the Netherlands Institute of International Relations, noted that France and Britain are the only European nations with a significant military presence in Asia.

But she says there are worries that France under Macron might overstep.

"France is up for it, but I think some Europeans are worried to see the French go there alone, too fast, or too strongly, at the risk of compromising relations with China," she said.

But the French task force to the Indian Ocean will include ships from Australia, Britain, Denmark, Portugal and the United States, according to the chiefs of staff deputy spokesman Colonel Guillaume Thomas.

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