A RAAF P-8A Poseidon (Image: AAP/CPL Craig Barrett, Royal Australian Air Force)

As Crikey reported earlier this week, when Australian ships and aircraft operate in the South China Sea, they’re not simply exercising freedom of navigation through the waters of China’s exclusive economic zone (EEZ). They are engaging in military espionage.

Here’s exactly what they are doing.

Our vessels drop hydrophones (microphones designed to operate underwater) mounted on a flotation device (a buoy). The buoy also carries a radio transmitter that transmits sounds detected by the hydrophone to an aircraft.

What gets detected?

  • Acoustic noise from a submarine’s turbines, propellers and other machinery
  • Water flow over the hull of a vessel once it goes above 10 knots
  • Propeller cavitation, which occurs when a high propeller speed creates bubbles in the water
  • Noises by the crew inside the submarine.

Each ship or submarine has an acoustic signature akin to a sonic fingerprint, which we use for identification purposes. We do this by comparing the signal collected by our sonobuoys with a previously recorded signature — remembering acoustic signals are affected by changes in water temperature, variations in depth and salinity and the nature of the seabed — and a vessel’s acoustic signature changes when its load changes, not to mention changes due to age, wear and tear, and modifications.

The library of signatures we’ve compiled enable vessel classification, identification, activities and capability. We do surveillance to record and update vessels’ acoustic signatures every six months or so.

Obviously these are all aimed at the People’s Liberation Army Navy. The US has also built a network of undersea and overhead sensors at choke points near China’s coastline, allowing it to monitor Chinese ballistic-missile submarines as they try to gain access to the open ocean.

The goal is to enable US hunter-killer submarines to trail them and sink them at the outbreak of hostilities, eliminating China’s nuclear deterrent (which is relatively small by US standards). One consequence is that China thus has an incentive to launch first if it believes an attack is imminent.

Remember, the US and Australia take the view that they’re allowed to do this within China’s exclusive economic zone — a view not shared by friendly countries like India, Indonesia and the Philippines. Malaysia, Vietnam, Brazil and Argentina don’t share it either. They take the view that warships have “no automatic right of innocent passage in their territorial seas”.

This intelligence-gathering is clearly integral to US and Australian planning for the possibility of conflict with China. The Chinese government — reflecting its view that if Western countries are going to conduct such activity within its EEZ, it will do the same — undertakes the same activities.

The problem lies with the lack of transparency and the reliance on the charade of “freedom of navigation” by the government. Our vessels and aircraft are there so that the US can more effectively destroy Chinese vessels as quickly as possible at the start of any conflict. This should be made clear to voters every time there’s an incident involving Chinese vessels or aircraft — along with the fact that regional allies take a different view from us.

Many voters may be entirely relaxed about that — but they’re not being told.

This is not to be conflated with China’s aggressive behaviour in the South China Sea, and its rejection of international rulings. It’s about whether our government — aided by security think tanks and much of the media — is prepared to mislead Australians about what our sailors and aircrew are doing far from home.