The US Navy has just received the world's largest unmanned vessel from Darpa, called the Sea Hunter Anti-Submarine Warfare Continuous Trail Unmanned Vessel (ACTUV). The vessel has been positioned as not just a submarine hunter, but also as a spy ship owing to its stealth capabilities.

The Pentagon first started work on the ACTUV in 2012, according to a report by Popular Mechanics, as part of its drive to increase unmanned systems in the land, sea, and air. The Sea Hunter will also serve as a platform to test autonomous surface ships in future.

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The Sea Hunter will also be a useful tool in experimenting how and in what ways an unmanned ship, travelling thousands of miles, for months on end without any people on board would fare. The vessel is also capable of tracking diesel electric submarines, notes the report.

The ship is 132ft long and weighs 140 tonnes and can reach a top speed of 27 knots, notes the report. The pilothouse, or the area where a normal ship would have the control station has been removed and the single hull vessel has two outrigger floats added to help it maintain stability out in the ocean.

The Sea Hunter reportedly was put to sea in 2016 and spent all of 2017 undergoing various gruelling tests, reports Popular Mechanics. Darpa came to realise that the Sea Hunter was good for launching the TALON-elevated sensor mast, which is a military parasail that can provide temporary communications. Talon can also deliver highly-valuable intelligence, surveillance, and reconnaissance (ISR) sensor packages, according to the report. It weighs 150 pounds and is dragged behind the Sea Hunter at an altitude of 1,500ft above sea level.

One way in which a drone ship can be used to track submarines is by laying low and waiting for submarines to surface. The report points out that most of the world's subs are conventionally powered, so the Sea Hunter can track them from a safe distance for weeks on end, something that a helicopter or spy plane cannot do. Also, a manned vessel could possibly become the hunted when tracking a sub. When the sub eventually makes it to the surface, a torpedo from the Sea Hunter could then neutralise it.

Sea Hunter
DARPA has successfully completed its Anti-Submarine Warfare (ASW) Continuous Trail Unmanned Vessel (ACTUV) program and has officially transferred the technology demonstration vessel, christened Sea Hunter, to the Office of Naval Research (ONR) DARPA

Darpa also realised that an unmanned ship, apart from the fighting and spying, has endless uses to the Navy. In fact, the Sea Hunter, during testing was reportedly referred to as the Payload Truck. Any kind of mission it undertakes from Somalia to the North Korean Coast, all can be accomplished in stealth and without putting a single soldier or sailor in harm's way.

Resupply missions, for example, could be carried out in dangerous waters, fuel, missiles, and even injured soldiers can be transported in and out of war zones.

Drone ships are also a major cost saver for the Navy. A single crew on shore can handle an entire fleet of ships. Large portions of ambling through open oceans can be done on the Sea Hunter's version of auto pilot.