The first warship to traverse open waters without a single crew member recently joined the U.S. Navy's fleet after eight years of development and testing.

And now nearly every element of the vehicle, known as the Sea Hunter, has become classified.

"About all I can tell you is that it has transitioned from [the Defense Advanced Research Projects Agency] to the Navy, and that's a success in the world of science and technology," said Rear Adm. Nevin Carr. "And that's a good thing, because that means that there's a there there."

Carr talked to CNBC about the vessel's status shift during the Sea-Air-Space conference, the largest maritime expo in the United States. He is uniquely familiar with the Sea Hunter since he oversaw its testing as chief of the Office of Naval Research and current development as Leidos vice president and Navy strategic account executive.