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Something is afoot in the western Pacific. Chinese oceanographic research vessels are appearing in ever larger numbers between the Philippines and Hawaii. These are the waters outside a line of islands from Okinawa all the way to Brunei commonly known as the first island chain.

A second island chain runs from the Japanese island of Honshu in the north, to Palau in the south. Both these chains consist mainly of US allies. Beijing feels they're hemming in China's access to the open seas.

While China's growing navy has made a lot of headlines venturing out of the first island chain, ships like this one have received much less attention. It belongs to China's fleet of maritime research vessels. Two dozen civilian ships that map the sea floor, measure water temperature and salinity, and record how sound travels in the depths of the ocean.

This data is needed for exploring mineral resources on the seabed, but also for naval operations. The US military has more than a dozen bases in the western Pacific. We've examined the paths of China's civilian survey ships over the last year based on positioning signals provided by MarineTraffic.com.

Twelve of these vessels have been criss-crossing the waters between the Philippines, Palau, Guam, and Japan with some forays further east. While Beijing has surveyed the South China Sea and the East China Sea previously, it is now on an unprecedented quest exploring the waters that could become the battleground for war with America, should that ever happen.

Some of the activity is related to mineral exploration. China has contracts with the International Seabed Authority for such exploration in an area east of Guam, and two southeast of Hawaii. The itineraries of the Xiang Yang Hong 3, Xiang Yang Hong 10, and Hai Cei are partly explained by this.

But the Chinese survey boats are making a lot of trips that can only be explained by military motivations. The Dongfang Hong 2 spent many days ploughing through waters east of Japan. Close to multiple US bases with naval, air force, and marine units. The Hai Da Hao conducted detailed surveys in two different areas of the Philippine Sea in waters US submarines are certain to use when sailing west from their base at Apra Harbour in Guam.

The Chinese government stresses the scientific role of these ships, but senior officials have said that the country must pursue more maritime resources and rights. And official statements have listed military objectives among the fleet's tasks.