HONG KONG • When a US Navy guided-missile destroyer sailed near one of Beijing's artificial islands in the disputed South China Sea this week, it was operating in a maritime domain bristling with Chinese ships.
While the United States Navy is expected to keep its technological edge in Asia for decades, China's potential trump card is sheer weight of numbers, with dozens of naval and coastguard vessels routinely deployed in the South China Sea.
Asian and US naval officers say encounters with Chinese vessels, once relatively rare, are now frequent, even at the outer edges of the controversial nine-dash line that Beijing uses to stake its claim to 90 per cent of the waterway.
Such encounters will only increase after US officials said the US Navy would conduct regular freedom-of- navigation operations akin to the patrol by the USS Lassen, which penetrated the 12-nautical mile territorial limit of Subi Reef in the Spratly archipelago on Tuesday.
"They are everywhere... and are always very keen to let you know they are there," said one US naval officer in Asia, requesting anonymity, referring to the Chinese navy and coastguard. "If you are in the South China Sea, you can expect to be shadowed."
Security experts said that in an actual conflict, the US technological advantage could be crucial, but China's numerical superiority had to be taken into account, particularly in any stand-off at sea.
Chinese warships followed the USS Lassen as it moved through the Spratlys. While the vessels kept their distance, China's patience could be tested by repeated challenges to the 12-nautical-mile limits that Beijing effectively claims around its seven man-made islands, experts said.
"China has homefield advantage," said retired Australian naval officer Sam Bateman, an adviser to the S. Rajaratnam School of International Studies in Singapore. "At any given time, they've got the numbers... and quantity, not quality, can be important in some situations", including confronting perceived intruders, he said.
Mr Bateman and several other regional security analysts believe that US warships could find themselves surrounded if China sought to prevent future freedom- of-navigation patrols.
Analysts and naval officers who have seen satellite images of the South China Sea over the past two years have described Chinese vessels keeping a semi-permanent presence at several disputed locations.
The list includes the Scarborough Shoal and Second Thomas Shoal off the Philippines, several isolated shoals in the Paracel islands to the north of the Spratlys and the South Luconia Shoals off the Sarawak coast of Malaysia.
The Chinese navy has also staged high-profile patrols off James Shoal close to Malaysia.
Mr Scott Bentley, a researcher at the Australian Defence Force Academy who has studied the South Luconia situation, said China had rotated coastguard vessels to maintain an almost constant presence there since January 2013.
"China is now for the first time in history not only clearly claiming the entirety of the nine-dash line, but is actively attempting to enforce its expansive claims within that area," he wrote recently.