Move over, aerial drones. The US military has a new, completely autonomous robot – and it operates on water.

The Anti-Submarine Warfare Continuous Trail Unmanned Vessel, or ACTUV, measures a staggering 132-feet long and 140 tons – over half as big as a blue whale. Its christening is scheduled for April in Portland, Ore.

Over the following 18 months, the vessel’s long-range capabilities will be observed by the Office of Naval Research and the Space and Naval Systems Warfare Command. Its first mission could come as soon as 2017.

According to Steve Walker, deputy director of the Defense Advanced Research Projects Agency (DARPA), the giant robot ship will be used for reconnaissance, resupply, and tunnel warfare.

“Imagine an unmanned surface vessel following all the laws of the sea on its own and operating with manned surface and unmanned underwater vehicles,” Mr. Walker said at a DARPA briefing on Feb. 10.

The ACTUV will use sonar to detect and follow diesel electric submarines and enemy vessels. It will get initial navigation assistance from Navy sonar buoys before its internal software takes over.

While complying with maritime laws and conventions for safe navigation, the unmanned system will help enable “missions spanning thousands of kilometers of range and months of endurance under a sparse remote supervisory control model,” according to its DARPA program information page. And as reported by Digital Trends, the drone can operate for about 60 to 90 days without a single crew member inside.

The submarine-hunting drone should drastically cut maritime expenses for the Navy, said Walker.

“We think the real cost savings will be in operating this vessel at sea compared to how we operate vessels today,” he told reporters. Missions will cost roughly $15,000 to $20,000 per day, compared to some $200,000 for comparable crewed naval vehicles. The ACTUV will also be able to carry larger payloads than most submarines.

At the DARPA briefing, the agency revealed that the underwater craft is part of a network of adaptable military systems designed to fight highly capable adversaries.

“We are an organization that has been designed from the beginning to take risk and manage risk in pursuit of off-scale impact,” DARPA Director Arati Prabhakar said. DARPA funding goes toward three primary goals: “rethinking complex military systems; mastering the information explosion; and developing the seeds of new technological surprise,” reported by the National Defense Magazine.

Autonomous drones are expected to play a critical role in achieving these goals, despite ethical concerns.

Konstantin Kakaes, a fellow at New America, a Washington-based think tank that has conducted extensive research into drones, told CNN that the ocean presented a rich environment for drones to function independently since communication with human operators is harder underwater and there are "no innocent bystanders to watch out for."

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But critics are concerned that further automating drones, the US and other military forces are developing robots that can kill without accountability, CNN reported.

In July, a group of concerned scientists, researchers and academics, including theoretical physicist Stephen Hawking and billionaire entrepreneur Elon Musk, argued against the development of autonomous weapons systems. They warned of an artificial intelligence arms race and called for a "ban on offensive autonomous weapons beyond meaningful human control."

Secretary of Defense Ash Carter said earlier this month that the US is currently developing "self-driving boats which can network together to do all kinds of missions, from fleet defense to close-in surveillance, without putting sailors at risk."

Meanwhile, Rear Adm. Robert P. Girrier, the Navy's director of Unmanned Warfare Systems, said at a January event that some of the technology is already here, allowing the US “to achieve supremacy at a lower cost."