Hidden Content
Unmanned warships could link up and cross oceans together.

Unmanned ships are smaller than manned ships, but that smallness results in ships less capable of crossing vast distances.
“Sea Train” would see many unmanned ships physically link to one another to overcome wave resistance, allowing these ships to make the longer trips.
While the U.S. Navy is busy buying a new generation of unmanned warships to serve along manned vessels, those smaller “ghost ships” may need to team up to make crossing oceans easier.
Future unmanned warships could journey across oceans physically connected to one another to make the trip more efficiently. DARPA’s new “Sea Train” concept is investigating the idea of ships that tether, like the individual cars in a train, in order to overcome wave resistance.

The Navy is plunging into the brave new world of unmanned surface vessels, or USVs. The service plans to buy a wide range of USVs, from medium-sized vessels (39 to 154 feet long) all the way up to large vessels (200 to 300 feet long). While small and difficult to detect, medium-sized vessels, or MUSVs, are also less capable of making a voyage of thousands of miles to hotspots such as the South China Sea and the Baltic Sea. The ships’ size restricts the amount of fuel each can carry, and wave resistance causes fuel-burning drag.

While MUSVs could always be physically carried into those areas—think ships like the M/V Blue Marlin, which can lift an entire U.S. Navy destroyer—larger carrier ships would need to be leased for service, or even built for the Navy ahead of time. And the whole point of building MUSVs is to reduce the amount of people and effort it takes to field a functional warship.

The Sea Train concept, C4ISRnet reports, involves MUSVs rendezvousing at sea, tethering to each other, and making a long distance trip together. The first ship in the formation encounters wave resistance—the rest of the ships, not so much. The many smaller unmanned ships together form one large virtual ship capable of self-deploying thousands of miles without the need for refueling.
In the event of a crisis, the Navy could sortie a half dozen MUSVs from Guam in the Pacific or Rota in the Atlantic. The ships would link up, sea train to the area of operations, and then disperse, each ship going its own way. Once the crisis is over, the surviving ships could sea train back to their home port.

DARPA’s effort to develop Sea Train will consist of two 18-month developmental and testing periods, followed by a reduced scale model that will provide a proof of concept. If successful, Sea Train could be deployed on unmanned U.S. Navy ships within a decade.

DARPA video of Sea Hunter, a prototype MUSV that recently made the trip from California to Hawaii, completely unmanned.