Economic and sovereignty interests are commonly cited as the reasons for China’s assertiveness in the South China Sea. To those reasons, however, could be added one more, the security of China’s sea-based nuclear deterrent. Since the founding of the People’s Republic, China has worried about external threats—and justifiably so. During the Cold War, it faced down both the world’s superpowers, first the United States and then the Soviet Union. Both were armed with nuclear weapons at a time when China was still developing its own. But even after it successfully produced nuclear-armed ballistic missiles, China could not rest easy. It still had to ensure their survivability to create a credible nuclear deterrent.