“How do you keep track of increasingly stealthy Russian, Chinese, and Iranian submarines? If you’re the U.S. military, you build a robotic ghost ship to follow them around the high seas. In 2010, the Defense Advanced Research Projects Agency, or DARPA, announced that they were building a 132-foot autonomous boat to track quiet, diesel-powered submarines. The program was dubbed Anti-submarine Warfare Continuous Trail Unmanned Vessel, or ACTUV.”
Source: US Military to Deploy Robotic Ghost Ships This Fall – Nextgov.com