"That's why we need autonomy," Sommer said. "We've got to have more ears and cover the ground reliably."
For engineers building drones, whether on land, in the air or at sea, one of the biggest problems to overcome is the so-called "sense-and-avoid" issue, or building a system that can detect other vessels or airplanes and move away.
Right now, for example, federal aviation authorities won't let drone aircraft fly over U.S. airspace, with a few exceptions.
International maritime laws say that each ship, whether it's supertanker, fishing boat or pleasure craft, must be able to "maintain an adequate watch," according to Sommer, and be able to avoid a collision. How that watch will be maintained with a robot ship is yet to be determined.
Once it is up and running, the robot ship will be able to sail for up to 80 days and travel 6,200 kilometers (3,852 miles) without refueling, according to DARPA documents.