A US military plan to build a crewless, automated robo-frigate which could trail hostile submarines across the oceans for months on end without supervision - the ACTUV project - is moving forward, with several contracts recently announced.

Distinctly limited in cocktail-party capability, but good for hunting submarines.

We reported on the ACTUV (Anti-submarine warfare Continuous Trail Unmanned Vessel) scheme back in February when it was announced. In essence the idea was to nullify the menace of cheap, very silent diesel-electric submarines - considered a serious problem by many in the major Western navies.

When such a submarine is located - for instance, it might be spotted leaving harbour and then submerging - an ACTUV vessel would in future be tasked to follow it. A next-generation air independent propulsion (AIP) sub of the sort now perhaps at last beginning to spread beyond Western-aligned nations could run submerged for thousands of miles, albeit slowly. Following it using ordinary manned frigates or submarines would tie up a lot of people and kit. The shadowing vessels would need to try and hold the quiet sub on sonar while staying outside the range of its weapons, a challenging task even with the latest low-frequency active sonars and one which would probably involve a lot of use of aircraft.

But an unmanned ACTUV, with no need to fret about being torpedoed, could sit right on top of the sub and track it easily. Being on the surface and thus able to run diesels and gas-turbines, it would have no trouble keeping up with the battery or AIP powered sub. And being unmanned would mean the ACTUV could be designed for the best possible performance and seakeeping, rather than for the convenience of its crew (see the pic). Probably the only part of the ACTUV that would normally be above the waves would be a combination funnel/engine intake and comms/sensors mast.

If the submarine captain, tiring of being shadowed, should torpedo his follower he would create what's known in the game as a "flaming datum" - his position would then be marked for all to see by the burning wreck of the robo-frigate and he would need to flee the scene of the crime. Sadly for him a diesel/AIP sub going at any speed submerged will run its batteries flat very fast - so leaving itself pinned to the map not far from the flaming datum, easy meat for responding ships or aircraft.

One major issue for the ACTUV would be the need for it to avoid crashing into other ships while trailing its unseen submerged quarry across thousands of miles of ocean, a task normally carried out by human watchkeeping officers who make course alterations in accordance with the International Regulations for Prevention of Collisions at Sea (aka the "rule of the road").

Instead the ACTUV will use an "artificial intelligence engine" originally developed for use in NASA's Mars rovers. Other Phase 1 study contracts have been handed out to the north American arm of controversial warboffinry selloff bonanza firm QinetiQ, and to sonar-analysis-cum-games-developer-and-audio-studio firm Sonalysts - perhaps most famous for producing submarine-warfare games such as 688 Hunter/Killer and Fleet Command, or possibly for their work with such artists as Aerosmith and Debbie Harry.

One should note of course that the ACTUV project is a brainchild of DARPA, the Defense Advanced Research Projects Agency, indicating in general that it has roughly the same chance of going mainstream with the US forces as does a legion of invincible warriors created by implanting the salvaged brains of dead soldiers into powerful mutated ninja gorillas. But that said, DARPA do score a hit every now and again - night vision, stealth, the internet - and they may do so again with ACTUV.

There is at least some chance that the US Navy's flagships of the future may command task groups composed at least in part of crewless, untiring robot ghost frigates - surely designated the Mary Celeste class if so. ®