March 19, 2025: In the 1990s, the U.S. Navy began developing robotic Anti-Submarine Warfare or ASW vehicles, in addition to very small ones the size of a torpedo. That led to the 2014 development of small robotic surface ships. One of these naval drones was the Anti-Submarine Warfare Continuous Trail Unmanned Vessel or ACTUV. This was a 41-meter, 145-ton ship designed to operate autonomously for up to 90 days, patrolling the high seas. ACTUV used a towed sonar array and other sensors to hunt for submarines. The top speed is 48 kilometers, but it cruises at about half that while working. No crew is on board, so up to 40 tons of fuel can be carried. The ship is slender but has two out-riggers for stability. ACTUV was designed to operate up to Sea State 5, which means six-meter waves and 38-kilometer-an-hour winds, and survive Sea State 7 and its nine-meter waves and 59-kilometer-an-hour winds. ACTUV will always have humans monitoring it and able to take control of the vessel and move it out of the way of major storms that go up to Sea State 12. Initially, a small compartment on the deck housed a human operator who could intervene immediately if an unforeseen emergency occurred. There was also a manned ship accompanying ACTUV for the initial tests before ACTUV was turned loose on its own. The first ACTUV was called Sea Hunter and, in 2016, underwent two years of sea trials. These were a success, and in 2020, the Navy approved the construction of ten ACTUVs, now renamed Medium Displacement Unmanned Surface Vehicles or MDUSVs.

ACTUVs were built to operate in the Pacific, where the Chinese fleet is, or the North Atlantic, where the rebuilt Russian fleet is. Mass-produced ACTUVs cost less than $25 million each and less than $20,000 a day to operate. That is less than a tenth of what a manned ASW vessel costs to build and operate.

Because ACTUV-type vessels operate on the surface without crews, there is the risk of someone getting on board and damaging the vessel or stealing technology or the entire vessel. This is a known problem with existing naval drones, which have been used to patrol harbors and coastal waters for years. Security measures have been developed that apparently work, and because of that, no one wants to provide any details.

ACTUV is a step up from earlier anti-submarine drones built to operate from LCS Littoral Combat Ships. Officially called the Fleet class Anti-Submarine Warfare Unmanned Surface Vehicle or ASWUSV, the 12.6-meter long boats weigh 8.5 tons and can carry 2.5 tons of sensors and other equipment. This drone can move up to 63 kilometers an hour and stay at sea for up to 24 hours. Most of the time, it would move slowly, using its sonar to search for subs. The ASWUSV has GPS and a computerized navigation system that allows it to run search patterns automatically. Thus, the sailors controlling the boat remotely can move it to an area where a helicopter or aircraft-dropped sonobuoys have picked up a contact and pursue it more intensively with the more powerful sensors it has on board. Such pattern searching worked out with algorithms derived from experience with what subs can do, has been a successful tactic since World War II. So far, ASWUSV has spent over 2,000 hours at sea operating autonomously.