Tweed said that the PLA's fleet of diesel and nuclear-powered submarines is a reflection of President Xi Jinping's goal to ensure the security of China's sea lines of communication amid territorial disputes in both the East and South China seas which have provoked discomfort among China's neighbors. To prevent US reconnaissance planes from detecting its presence, the caves constructed beneath the surface of the South China Sea are crucial for China's submarine fleet.
Hainan has become a major base for the PLA Navy as tensions in the South China Sea escalate. While Sanya Bay has become more built up, Yalong Bay, in the west, is a new development site for the navy, according to Felix Chang, a senior fellow at the Foreign Policy Research Institute in Philadelphia. Chang said that there is a surface vessel base with two long piers capable of mooring an aircraft carrier to the north.
Chang also said that there is likely a base designed for nuclear-powered submarines. Another four piers seem to be able to moor eight submarines. The 16-meter wide underwater tunnels leading to the cave under a hill are located south of those piers. Among China's five nuclear-powered submarines, three are capable of launching JL-2 ballistic missiles and five more may begin their service with the PLA Navy soon, according to a Pentagon report.
Since the end of World War II and the establishment of the People's Republic of China, Hainan has been considered a major submarine base for the Chinese. With the presence of three Type 094 Jin-class attack submarines in Hainan, China has become more aggressive in the region. While an oil rig deployed by Beijing to disputed waters near the Paracel islands which Vietnam claims as part of its exclusive economic zone triggered anti-Chinese rallies in Vietnam this May. There has also been tension over China's land reclamation projects on the disputed Spratly islands.
A pair of PLA Navy's Type 094 Jin-class attack submarine.