An experimental, self-piloting ship, which has been built to travel over the open seas for months at a time hunting submarines without a single crew member aboard, has begun tests.
The 132ft-long (40m-long) unarmed prototype, dubbed Sea Hunter, is a product of the US Defense Advanced Research Projects Agency (DARPA), which develops new technologies for the military.
DARPA says the vessel is the first of a new class designed to hunt for enemy submarines, travelling thousands of miles before needing to stop.
It was launched earlier this year at its construction site in Portland, Oregon, and conducted speed tests in which it reached a top speed of 27 knots (31 mph/50 kph).
This week's testing will focus on ensuring that it can safely adhere to international norms for operating at sea, using radar and cameras to detect other vessels and avoid collisions with them.
Open-water testing is planned to begin in summer 2016 off the California coast, with the Sea Hunter designed to cruise on the ocean’s surface for two or three months stretches without a crew or anyone controlling it remotely.
The Pentagon, meanwhile, has hailed the development as a major advance in robotic warfare.
It hopes that the vessel's unprecedented levels of endurance and autonomy could make it an extremely efficient submarine hunter, able to operate at a much-reduced cost to the Navy's manned vessels.
The ship’s expected £14 million ($20m) price tag and its £10,000 to £14,000 ($15,000 to $20,000) daily operating cost make it relatively cheap for the US military. Rear Admiral Robert Girrier, the Navy’s director of unmanned warfare systems, has said:
"You now have an asset at a fraction of the cost of a manned platform.”
Deputy US Defense Secretary Robert Work, meanwhile, is quoted as saying by Reuters:
"This is an inflection point. This is the first time we’ve ever had a totally robotic, trans-oceanic-capable ship."
He added that he hoped these kinds of ship could be operating in areas like the western Pacific and the Gulf within five years, and also talked about the possibility of fitting weapons onto the Sea Hunter.
It comes after calls were made last year by leading scientists and human rights groups for a global ban on developing artificially intelligent robots
Some fear that armed, autonomous robotic systems could identify people as threats and kill them - but Work said any decision to use lethal force would always be made by humans:
"There’s no reason to be afraid of a ship like this," he added.
The move to develop the Sea Hunter is part of a Pentagon strategy to incorporate unmanned drones into the military's air, land and sea resources, with increasing autonomy.
It also comes during a time of Chinese and Russian naval investment, with the expansion of China's submarine fleet reportedly raising concerns over the vulnerability of the aircraft carrier battle groups and submarines that remain crucial to US military superiority in the western Pacific.
Peter Singer, an expert on robotic warfare at the New America Foundation think-tank, said:
"We’re not working on anti-submarine (technology) just because we think it’s cool. We’re working on it because we’re deeply concerned about the advancements that China and Russia are making in this space."
Work says he hopes the ship will be able to continue testing with the US Navy’s 7th Fleet, based in Japan, once it is proven safe.
In future, ships like the Sea Hunter could operate on a range of missions, possibly even including counter-mine warfare operations, all with limited human supervision.