Australia's strategic environment changed a week ago, even if much of our media did not notice. Last weekend, a Chinese taskforce of three warships steamed south through the Sunda Strait to conduct combat simulations and other exercises in the Indian Ocean, somewhere between Indonesia and Christmas Island.

The vessels, two destroyers and an advanced 20,000-ton amphibious ship capable of carrying some hundreds of marines (pictured), then skirted the southern edge of Java before heading north through the Lombok and Makassar Straits and into the Pacific.

This is the first substantial Chinese military exercise in the eastern part of the Indian Ocean and in Australia's maritime approaches. It seems also to be the first time a Chinese taskforce has transited the Sunda and Lombok straits as alternatives to the Malacca Strait.

With this decidedly Indo-Pacific foray, China is sending many signals, deliberately or not. One is about its ability and ambition to project force through and beyond the South China Sea. Another is its wish to be seen to be interested in protecting its commercial sea lanes into the Indian Ocean. A third is that the People's Liberation Army-Navy will go where it wants when it wants, without necessarily consulting or forewarning local powers.

A fourth is that the islands of East Asia are not a meaningful 'chain' to constrain China's military reach. In that sense, this exercise should be seen alongside a larger activity in the western Pacific last October.

To be clear, there was nothing illegal or fundamentally hostile about what the Chinese navy has just demonstrated. A greater Chinese security role in the Indian Ocean is inevitable and at one level a corollary of China's economic interests.

Even so, this recent episode is bound to raise questions in national security establishments across the region, including in India and Indonesia as well as in Australia. I will have more to say about that next week in a joint opinion article with prominent Indian strategist Raja Mohan (a Lowy Institute nonresident fellow and incidentally my co-chair in a major Australia-India dialogue that kept us busy this week).

Although the Chinese navy may have surprised us all with the precise timing and nature of its Indo-Pacific venture, nobody can accuse Beijing of a lack of transparency in its public reporting during the event.

Indeed, the coverage of the exercise in the Chinese media and on social media is a textbook case for intelligence analysts and policymakers in how so-called 'open sources' can provide early warning of change in the strategic environment – earlier, I suspect, than much of the secret stuff.

I first learned of the exercise six days ago, with help from a friend who makes a habit of monitoring Chinese-language press, the magic of Google translate, as well as a tweet from American China expert Taylor Fravel. Within another day or two, Chinese state television was proudly reporting, in English and in some technical detail, about the Indian Ocean drill. These and other Chinese reports were more than enough to piece together a clear sense of the route and activities of the three ships, as well as the historic nature of their voyage.

Yet days passed before much of this made it into the international English-language media, and I am yet to see serious news coverage in Australia (the Hindu's excellent China correspondent was a little quicker off the mark).

The precise strategic implications of the Chinese navy's newly-demonstrated ability to operate in Australia's northern approaches are open to debate. Neither China nor Australia wants a confrontational relationship. The idea that China might pose a direct military threat to Australia remains far from mainstream in our strategic debate. Australia has rightly sought to engage China as a security partner in recent years, for instance in disaster-relief exercises.

Even so, it is a safe bet that the voyage of the three Chinese warships Changbaishan, Wuhan and Haikou will prove far more consequential to Australia's strategic future than any number of those certain other vessels in the waters off Indonesia that have so dominated our media and political attention of late.

Photo courtesy of Sinodefence Forum.