According to Greek mythology.

• Author: Insinna, Valerie

According to Greek mythology, the deadly, serpent-like Hydra was nearly undefeatable. Cutting off its head would cause it to grow two back in its place, rendering the creature exponentially more dangerous.

Military agencies and defense contractors have created design concepts and fledgling programs that embody Hydra's survivability and versatility--a huge fleet of small platforms that can be used to surprise and overwhelm an enemy that thought it had the advantage. Although the amothershipn concept isn't new, experts say it may grow increasingly relevant in future years.

The Defense Advanced Research Projects Agency was inspired by the Greek myth to create the Hydra program. Its version of the many-headed serpent is a collection of unmanned payloads and platforms that lie dormant on the ocean floor for weeks and months before being deployed.

The Navy currently relies too much on large, advanced ships and submarines that carry out many different missions, DARPA information said. Even though these vessels are highly survivable and capable, they can only be in one place at a time. Rather than stretching themselves thin, unmanned platforms can help the service project power at less cost than building new ships.

"The climate of budget austerity runs up against an uncertain security environment that includes natural disasters, piracy, ungoverned states and the proliferation of sophisticated defense technologies," Scott Littlefield, DARPA's program manager, said in a news release. 'An unmanned technology infrastructure staged below the ocean's surface could relieve some of that resource strain and expand military capabilities in this increasingly challenging space."

DARPA wants to develop a modular enclosure--a kind of mothership that will transport, house and launch payloads while traveling throughout littoral waters, a 2013 broad agency announcement stated. The enclosure will be able to conduct all operations without surfacing, meaning that it must have sufficient energy, propulsion and command-and-control capabilities to complete an entire mission.

That mothership drone would deploy even more unmanned vehicles underwater, in the air or on the surface of the ocean. Hydra's underwater payloads could tackle missions including mine countermeasures and intelligence, surveillance and reconnaissance. However, most of their focus "will be on safely transporting existing undersea vehicles, providing the required energy for long endurance, efficiently...