The Anti-Submarine Warfare Continuous Trail Unmanned Vessel or ACTUV is a high-tech unmanned robotic vessel, designed by DARPA, that is designed to make it possible to sniff out hostile submarines without a human crew.
Also known as the Seahunter, this 42 meter-long vessel is capable of working for months at a time. This makes it possible for the unmanned vessel to be used safely -- and in tune with international maritime laws -- at only a tenth of the cost of typical submarine-detecting vessels. The ACTUV is capable of operating for between 30 and 90 days at a time without any human crew, and can depart from and arrive back at ports autonomously.
This unmanned vessel is a great example of how operational efficiency of a maritime war vessel can be increased whilst also decreasing risk to human operators.