The United States Navy is carrying out the biggest overhaul of its top-secret undersea surveillance network since the end of the Cold War in an effort to contain the threat of China’s submarines. Beijing has similar plans of its own.

The U.S. Navy is carrying out the biggest overhaul of its top-secret undersea surveillance network since the 1950s as China’s naval power surges and new technologies are fast reshaping maritime warfare. Beijing has similar plans of its own.