HOT WATER : ''SOUTH CHINA SEA SONAR''

IT is hard to sail across the South China Sea without bumping into a warship. On September 30, last year, an American destroyer passed within 50 metres of a Chinese naval vessel which was conducting ''unsafe and unprofessional'' manoeuvres, according to the Americans.

Earlier in the month Japan sent a submarine to conduct drills in the sea for the first time.

In August a British warship was confronted there by Chinese ships and jets,. And later ships from Australia, Singapore, Malaysia, New Zealand and Britain took part in more than two weeks of joint naval drills in same crowded waters.

The maritime hubbub is an attempt to push back against China's claim to the entire South China Sea, which other littoral states dispute and which a UN tribunal has rubbished.

China wants military vessels and aircraft to notify it before passing through the sea, something America's and others would view as an infringement of international  norms even if China's claim had been withheld.

To make matters even more fraught, China has reclaimed land around a  series of reefs and rocks in the sea to build bases teeming with guns, missiles and radar.

Should these constructions be deemed rocks or islands under international law, and rightful Chinese territory, then certain restrictions would apply to military vessels passing within 12 nautical miles.

But America and the UN tribunal, among others, consider several of them ''low tide elevations''     -shoals, in effect - that do not enjoy the same rights.

America and its allies keep sending warships to sail around the sea in ways that demonstrate that they do not accept China's position.

Since 2015 America has conducted 12 of these ''freedom to navigation operations'' .

These flout China's claims in several different ways. By sailing within 12 nautical miles of  genuine islands, for example, America's navy demonstrates that it does need to and will not seek permission to exercise its right of ''innocent passage''.

By conducting military maneuvres within 12 nautical miles of other fortified specks, it shows that  it considers them mere elevations around which no restrictions are warranted.

And by entering the sea at all, it rejects China's stance that it has any say in military activity in open waters within the area it claims.

Australian, Japanese, British and French vessels have all sailed across the sea together, in various pairings. The hitch is is that there are a lot more warships ploughing around, and so a lot more scope for dangerous heated encounters.

The World Students Society thanks The Economist, and will continue to research and watch this growing Hot Spot.