One of the biggest problems the US Navy faces today is the threat of quiet, short-range diesel-electric submarines. When running on batteries alone, these subs are extremely difficult for the Navy's ships, subs, and patrol craft to detect with passive sonar. In war games with US allies—and in recent propaganda-generating "drills" by Iran's navy—US ships have consistently ended up in the periscope crosshairs of diesel submarines that have gone undetected or that the Navy has simply lost track of. The best way to keep tabs on diesel submarines is to literally stay on top of them, tracking them with subs or ships from the moment they set out to sea until they return home.

This is the sort of thing the US Navy used to do with Soviet submarines operating off the coast of the US. The problem is that doing it for diesel submarines in distant parts of the world would tie up ships and sailors, pulling them away from other missions—and the US Navy doesn't have the same sort of resources for antisubmarine warfare that it had during the Cold War to bring to bear (in terms of the sheer number of antisubmarine warfare ships in the fleet) on the diesel-electric subs of potential adversaries. This is especially true for those operating in waters far from the US, in places like the Persian and Arabian Gulfs, and the western Pacific. That's a problem that a Defense Advanced Research Projects Agency project now nearing fruition seeks to solve with drone ships.

During a roundtable with media last week, Darpa Deputy Director Steve Walker announced that the agency and its contractor Leidos would launch the first full prototype of an autonomous ship designed to hunt submarines and trail them for weeks at a time. Eventually, autonomous vessels could be deployed to track the latest generation of quiet diesel-electric submarines over distances of thousands of miles, providing targeting information to US Navy submarines, ships, and patrol planes—or simply harassing the subs with relentless active tracking to deter them from carrying out their mission.

The technology could also be used for unmanned ships used to search for underwater mines and carry out resupply missions or act as a communications relay. And these ships all would operate at a fraction of the cost of conventional manned ships—costing $15,000 to $20,000 per day to operate instead of the $700,000 per day it costs to deploy a destroyer for the same job.

The prototype, named Sea Hunter, was built under DARPA's Anti-Submarine Warfare Continuous Trail Unmanned Vessel (ACTUV) program, a project jointly funded by the Navy's Office of Naval Research and Space and Naval Warfare Systems Command. Measuring 132 feet long and displacing about 140 tons—roughly the size of a large fishing boat and a third the length of the Navy's LCS ships—the Sea Hunter will be christened in Portland, Oregon this April and begin testing in the Columbia River before undertaking long-range testing in the Pacific over the next 18 months.

Leidos (the national security and healthcare research company that split off from SAIC) conducted testing of the ACTUV program's navigational and collision avoidance software last year, installing it on a 40-foot work boat that autonomously sailed 35 miles of the Intracoastal Waterway from Gulfport, Mississippi to Pascagoula without human intervention. It used commercial off-the-shelf radar, GPS, and a preloaded navigational chart to successfully stay in channel and avoid other boats, buoys, and underwater navigational hazards.

Early in the ACTUV program, DARPA performed a bit of crowdsourcing to help develop ACTUV's sub-hunting tactics by harnessing gamers. The ACTUV Tactics Simulator, based on Sonalysts Combat Simulations' Dangerous Waters antisubmarine warfare game, was used to collect data on players' success and failure to assess approaches to submarine tracking for use in the ACTUV tactical software. DARPA and the Navy may soon get to see the fruits of gamers' efforts. If they like what they see, the program could be turned over to the Navy to become a "program of record" within the next few years.