As a U.S. Navy aircraft carrier, loaded with 60 aircraft and more than 6,000 sailors, heads toward port, it's protected by a group of 10 or more small boats.
The boats move around the ship, scanning for suspicious and potentially hostile vessels coming too close. If they spot a potential adversary, they race toward the intruder, working together to swarm around it and block it from getting any closer.
If necessary, they can destroy an attacking vessel.
What makes this scenario unique is that these small boats are unmanned. No one's driving them or on the look out. No one's manning the machine gun.
The Office of Naval Research has created an autonomous boat system and recently tested up to 13 unmanned boats working together, according to Rear Admiral Matthew L. Klunder, chief of naval research. "It's not just the fact that we've developed this technology, but we've exercised it," he said.
The Navy expects to officially deploy the autonomous system -- dubbed CARACaS or Control Architecture for Robotic Agent Command and Sensing -- in about a year.
"We all recognize we live in a pretty volatile world," said Klunder. "There are sailors in harm's way trying to avoid conflicts and stabilize a region. We want to make sure that those sailors, those soldiers, are never in a fair fight. We want them to have the most innovative technologies available."
The technology, which uses artificial intelligence, machine perception and distributed data fusion, was successfully demonstrated over two weeks in August on the James River in Virginia.
"This is a huge advance for robotics and, specifically, for object recognition and artificial intelligence implementations," said Patrick Moorhead, an analyst with Moor Insights & Strategy. "These are the smartest robots I have seen. The combination of speed, object recognition and artificial intelligence is very, very impressive."
The fact that a computer system can distinguish a potentially suspicious boat from any other vessel is a huge advance.
"It is very difficult to determine a threat versus friendly because there could be nuances in the way the boat moves, the way it turns, its speed, the way it reacts to the swarming boats, the people on deck, what they're carrying and the way they are acting," added Moorhead.
In October 2000, the USS Cole, refueling in a Yemeni port, was damaged, 17 American sailors were killed and 39 were injured when it was bombed in a suicide attack made in a small craft that simply drew up beside the ship.
The Navy hope the new autonomous system will prevent such an attack from happening again.
"If we'd had this capability there on that day, we would have saved that ship," said Klunder. "We don't want to ever see that again. We want to save sailors' lives. We want to save sailors and ports and ships."
A Mars-based autonomous system
Work on the CARACaS system, which could one day be adapted for underwater, ground and aerial vehicles, began in 2004 as an applied research program, with scientists looking initially to create an autonomous system to operate a single boat.
"At that time it was a huge technical challenge," Robert Brizzolara, program manager for the Office of Naval Research, said. "I wasn't thinking at the time about group or team operations. It wasn't really until 2007 or 2008 that I actually started doing tech development for group or team operations."
To get going, Brizzolara and his team began by using autonomous control technology that NASA developed for the Mars rovers Opportunity and Spirit, both launched in 2003. NASA's Jet Propulsion Laboratory, along with Johns Hopkins University and the Naval Surface Warfare Center, joined the Office of Naval Research team.
The autonomy software for the rovers needed a lot of adaptation -- notably because the rovers move slowly over a distant and dangerous ground terrain while the boats need to move at high speeds over water to intercept, block or swarm around suspicious craft.
"Thinking about the difference between a boat and the Mars rovers -- the speed and the environments they operate in -- it was a significant amount of work to adapt the Mars rover system to one that can operate a boat," said Brizzolara. "They're such different vehicles. The control system for the boat needs to respond much, much more quickly."
The CARACaS system was developed around two main points of emphasis, he explained.
First, the control system needs to use cameras, radar and sensors to perceive other vessels, the shoreline and anything else that needs to be avoided or monitored.
Second, the boats need to plan their movements and their reactions to suspicious vessels or objects in the water.
If five boats are working together, for instance, all five will share the information they're picking up from their own radar and sensors with each other. That means each boat has information from all the others about they're "seeing," as well as each one's position, speed and actions.
The information is shared over a network radio link at this point, though Brizzolara said the Navy has more secure information networks and will put one in place before the system is put into official use.
"The boat system needs to plan its own route," Brizzolara explained, noting that he cannot divulge exactly what speeds the unmanned boats reach. "We have developed a much faster route planner for the boat that works in close to real time to process those routes at speeds appropriate to what boats of that size should be doing."
He added that the Navy has built various military tactics into the autonomous software, using AI to enable the boats to, on the fly, designate a target, block it, encircle it and engage it if need be. The boats also could trail each other or a ship; go into escort mode; or line up in a blocking behavior.
"The key is its flexibility to execute any number of behaviors, not just swarming," said Brizzolara. "We would like, from a science and technology point of view, for CARACaS to be as widely applicable as possible. The fact that it can be programmed to undertake a number of different behaviors means it could take on a wider range of missions."
Dan Olds, an analyst with The Gabriel Consulting Group, said the power of the CARACaS system lies in its complex combination of technologies able to work together.
"These are definitely more sophisticated than the vast majority of robots we've seen to date," he said. "The programmed behavior with all the actors moving in concert is a big advance, particularly when considering all of the variables they will have to contend with, like ocean waves, winds and rain."
Using an array of sensors and radar, the system is able to process all of the inputs, like imaging, conditions, mission and the actions of others. "That," said Olds, "is a big deal. When taken together, this is a big step for robotics."
The autonomy system can be installed in any small Naval vessel. The boats themselves do not need to be specially built.
"We've designed team behaviors into the system," said Brizzolara. "It's a system developed to replicate functions that a boat driver would normally do.'
Moorhead noted that before CARACaS, a lot of military robotics had limited ability to work cooperatively with each other and limited object recognition.
"It's difficult to get multiple robots to work together because they need to be aware of the entire system of robots, instead of just their surroundings," he said. "This raises the challenge exponentially."
Robotic deterrence and firepower
The boats are equipped with non-lethal weapons such as sound cannons and bright lights designed to confuse or disorient enemies. If needed, the boats can fire upon and destroy an enemy boat.
The autonomous system cannot do that, though. If lethal force is required, a human will have to make that decision and enable the boats to fire on a target, Klunder emphasized.
"We have every intention of using these unmanned systems to engage a threat and destroy it if necessary," he said. "But there is always a human in the loop on the designation of a target and the destruction of a target. The power of what I'm holding here is the autonomous feature. They sense, avoid, go get and engage with a target. They work together."
For now, Brizzolara said his group is working to meet the Navy's goal of having these autonomous systems working in a year.
Their biggest challenges, he noted, are improving the system's perceptive abilities and the boats' ability to work together.
"There are still refinements that we need to do in terms of the major components of the system," said Brizzolara. "We need more reliable sensing so we see everything that's out there and more reliable route planning for multiple boats working together. If one boat needs to take itself out of the team to go investigate something else, the team needs to compensate for that one removed boat."
One of the biggest problems researchers face is making sure the boats are operating from the same information and that they are working together to decide what to focus on and how to move as a swarm.
"We've taken that first step, but there is still work we need to do," said Brizzolara. "We need to continue to develop the algorithms for the route planning and then we need to do simulation testing and then [go] out and test it on the water."
The Navy is looking to use the system around large naval vessels, merchant vessels, ports, harbors and oil rigs.
"We've taken a patrol craft usually manned with three or four sailors each and made it unmanned," said Klunder. "All those sailors normally on those crafts can be back on the ship and out of harms way."