South China Sea Bases
The Chinese government have undertaken a very impressive building effort in the Spratley and Paracel Islands in the South China Sea as they look to expand their maritime ambitions. This has caused a number of international disputes, most notably with the U.S. as the project has seen the creation of 3,200 acres of new land and little is known about its true purpose.
Anyone who gets to close to the islands are immediately confronted with Chinese forces demanding they leave the area, and they have surface-to-air missiles and ground-launched missile systems to back them up. It is known that the area houses radar facilities and used for missile launches, but what else goes on remains a mystery. Curiously though, in 2016 the Chinese government announced that they intended to build an underwater base 10,000 feet below the surface.