'China has constructed an underground and underwater submarine facility on Hainan Island as part of a major buildup of naval forces in the South China Sea. Satellite imagery from publicly available Google Earth shows the underwater submarine tunnel entrance located several miles south of the major Chinese naval facility at Yulin, on Hainan Island, which is strategically located close to the shipping lane from the Strait of Malacca.'

Source: http://www.east-asia-intel.com/eai/

Full post on Ogle Earth

Note: Another submarine tunnel was posted on in February on Ogle Earth.

Hi,
i've added some new informations about this naval base.
Here's the link :

http://bbs.keyhole.com/ubb/showflat.php?Cat=0&Number=1165443&page=0&vc=1#Post1165443