According to a prominent American defense journal, China is building an underground nuclear submarine base on southern Hainan Island. From AFP:
Jane’s Intelligence Review, a respected defence periodical, said satellite images of the base from imagery provider DigitalGlobe were the first confirmation of its existence.
Although Beijing is displaying no overt aggression, the base could mean an increase in its strategic capability in the South China Sea and considerably further afield, Jane’s analysis said.
…The Daily Telegraph, which reported the satellite images, called the base a “vast, James Bond-style edifice capable of concealing up to 20 nuclear-powered submarines, which will enable China to project its power across the region.”