How Beijing is using 'fishing militia' to assert its claims in the South China Sea

In the early hours of September 8, two Philippine boats and their two coastguard escorts sailed towards the contested Second Thomas Shoal in the South China Sea.

It was their third mission in five weeks to deliver food, water and fuel to troops on the submerged reef in the Spratly archipelago.

To Beijing, those troops - who use a grounded World War II warship as a base - are illegally occupying the Chinese territory of Renai Jiao. The reef is controlled by Manila but also claimed by Beijing, Taipei and Hanoi.

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As the Philippine vessels neared the reef, Chinese ships stationed nearby tried to stop them, according to data from ship tracking site MarineTraffic.

One was a coastguard vessel but the other eight Chinese ships were apparently fishing boats.

Four of the steel-hulled civilian ships sailed with the Chinese coastguard vessel, taking turns to block the Philippine coastguard ships BRP Cabra and BRP Sindangan from getting close to the reef.

Four more civilian ships were standing by as three more Chinese coastguard vessels surrounded the Philippine boats.

The Chinese ships came within metres of the BRP Cabra's hull, video footage released by the Philippine coastguard showed. The Philippines said the Chinese vessels' "dangerous manoeuvres" had endangered the crew and that their presence in its exclusive economic zone (EEZ) was illegal, but the resupply mission was completed.

The incident is an example of how China is increasingly using civilian ships to assert its territorial claims to nearly all of the resource-rich South China Sea.

Its neighbours are concerned that Beijing is seeking to achieve its goals by blurring the lines between civilian and military forces, and by using force such as firing water cannon.

These so-called grey zone tactics are used by governments to compel others to act in a certain way while enabling them to deny responsibility for what are seemingly civilian activities.

Ray Powell, director of SeaLight, a Stanford University project focused on grey zone activities in the South China Sea, said there should be clear demarcation of troops and civilians in conflicts to avoid civilian casualties - a principle struck after the immense loss of civilian lives in World War II.

"Once you start blurring that, then it becomes very hard to decide who is a lawful target," Powell said. "That then leads us into places that are scary places."