Australia has stepped up military surveillance flights over the South China Sea in a signal to Beijing that it means to continue operating in the regional flashpoint area despite heightened tensions provoked by territorial disputes.
In a move that is likely to grate with the Chinese government, an RAAF P-3 Orion aircraft carried out patrols in the air space in recent weeks, prompting a demand from Chinese naval forces in the waters below to explain itself.
Defence confirmed the recent flight, though only after the plane's presence happened to be noticed by a BBC journalist in the area, who recorded an Australian crewman telling the Chinese navy that the plane was "exercising international freedom of navigation rights". 
While such surveillance flights have been conducted for years in the South China Sea under Operation Gateway, their tempo has been increased in the past 12 to 18 months, it is understood. This amounts to a calculated signal to Beijing that Australia does not accept the sea territory claims generated by China's building of artificial islands in the area, which is subject to claims by Malaysia, the Philippines, Vietnam and others.
The government played down the patrol, saying it was a routine part of Operation Gateway.
But experts said it sent a clear message - that Australia would not yield space to China's growing ambition to unilaterally control the strategically important waters.
Crucially it comes amid heightened tensions after a US destroyer sailed close to one of China's artificial islands in late   October in a so-called "freedom of navigation" exercise.
James Goldrick, a retired naval officer who is now advising the government on its upcoming Defence White Paper, said the RAAF's flight could be interpreted as a challenge by China.
"The signal is that we'll continue with our routine operations," he said. "Inherently it is an element of challenge and what it's saying is we're doing our normal things that we've always done within the requirements of international law."
Benjamin Schreer, a strategic expert with Macquarie University, agreed Australia was making a point. "Apparently the pilot seems to feel the urge to convince the Chinese navy ... that we have every right to be in that airspace ... This really takes place in a changing strategic and political context."
Peter Jennings, executive director of the Australian Strategic Policy Institute, said that "nothing is routine in the South China Sea right now because of the heightened state of tension in the region".
But he said it was "ridiculous" that the flight was revealed by a journalist. The government should publicly state what it was doing to send the strongest possible signal to Beijing, he said.
The experts agreed such flights did not pose any major risk to RAAF planes.
BBC journalist Rupert Wingfield-Hayes was on another plane close to the disputed Mischief Reef near the Philippines when he recorded the voice of an Australian airman who'd been called to account by the Chinese navy. He published a story describing the encounter on Tuesday.
"China navy, China navy," the airman is heard saying. "We are an Australian aircraft exercising international freedom of navigation rights, in international airspace in accordance with the international civil aviation convention, and the United Nations Convention on the Law of the Sea - over."
The Chinese did not respond further.
Sam Bateman, a former navy officer now with the University of Wollongong, said that this was a standard call. "That's the sort of radio call they'd make if they were going near a foreign warship. It's purely a safety measure that the ship knows whose aircraft this is, what it's doing sort of thing."