The U.S. Navy is working hard to improve the cybersecurity of its computer networks and weapon and communications systems, while bracing for potential attacks on power grids and fuel supplies, Navy Secretary Ray Mabus said Wednesday.

Mabus said cyberwarfare was a clear threat, given Russia's use of cyberattacks before its physical invasions of Crimea and Georgia.

"We've got to pay a whole lot of attention to this," Mabus said at an event sponsored by Defense One media group. "Cyber is in everything now. It's not just weapons systems. It's in every system because we are so networked."