The U.S. Navy is investing billions of dollars to revamp its Cold War-era submarine detection system in the Pacific Ocean as China bolsters its own navy and becomes more belligerent.

The U.S. Integrated Undersea Surveillance System was first built in the 1950s as a top secret program aimed at countering Russia’s naval capabilities in the Cold War. Now, however, the fleet of surveillance ships and maze of undersea sensor cables are being modernized, three people with direct knowledge of the effort told Reuters.

The modernization effort aims to make the surveillance cables smaller while covering a larger area. The U.S. is also selling the same technology to Australia.