Illustration by John MacNeill: SPLIT STRIKE

Deployed from a sub's hull, Manta could dispatch tiny mine-seeking AUVs or engage in more explosive combat. Photo by Illustration by John MacNeill

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Sheathed in a chilling veil of
rain, under cover of darkness, a few Navy Seals descend from a ship into a small rubber boat. They motor to a nearby harbor, idle the engine, and gently lower three torpedo-shaped objects into the water. The mission? Locate that persistent nemesis of amphibious operations: undersea mines. But tonight, instead of the specially trained dolphins or human divers who would normally do this work, the Navy is relying on robots.



This scene has been enacted many times recently in San Diego, Seattle, Hawaii and the Mediterranean. It's a test scenario, a dress rehearsal for the real thing. Naval experts won't say whether their smart new unmanned subs, known as autonomous underwater vehicles (AUVs), will be sent into hostile harbors anytime soon -- that's classified -- but they do express deep satisfaction with how the machines are performing.



The U.S. Navy has built its dominance on the conviction that bigger is better, but the nature of warfare is changing. In the post-USS Cole era it's clear that the most ironclad expressions of might are vulnerable to a couple of guys in a rowboat. Early in the Persian Gulf War, the warships Tripoli and Princeton were blown open by mines -- devices costing a few thousand dollars causing millions in damages. Unable to land, the Marines had to be airlifted in. Mines and other easily acquired technologies such as cruise and ballistic missiles mean that today any nation, no matter how technologically humble, can effectively bar U.S. forces from its coastline. In military parlance the problem is known as "broad-area denial."



One way for the Navy to become more agile would be to employ unmanned submarines, which in the past decade have blossomed at university research labs and have been commercialized by small spin-off companies [see "Robots of the Deep Blue Yonder," Feb.]. But though the Navy funded some early AUV development, like most large bureaucracies it was slow to incorporate novelties into its long-range planning. In April 2000 a Navy committee warned that robot-sub technology was available in the global marketplace and that if the agency didn't wake up, it would fall behind. The committee's report outlined four desirable "signature capabilities" for the AUV fleet of the future -- reconnaissance, undersea search and survey, communications and navigation, and anti-submarine warfare -- and the Navy has since stepped up its AUV research and development.



Building these devices won't be easy. While a few AUVs -- like those the Navy Seals used in their mine-hunting test -- are already operational, their capabilities fall far short of what military planners ultimately envision. Better sensors, signal processing, energy sources and navigation methods will be necessary before AUVs can fulfill their potential role.



Operating unmanned submarines is far more challenging than flying unmanned aircraft like the Predator, which, controlled by a remote pilot, made successful sorties last year in Afghanistan. And the issue isn't just autonomy. "Everything's working against you underwater," says Robert Wernli, a longtime AUV proponent at the Ocean Systems Division of the Space and Naval Warfare Systems Center (SPAWAR) in San Diego. In the ocean, visibility is much lower than in air. Currents pull vehicles off their plotted course. Saltwater corrodes them. Radio signals and GPS don't penetrate deep water, which makes navigation and communication especially challenging.



But the military benefits AUVs promise almost certainly justify the effort. Nearly undetectable -- they operate fully submerged and have low acoustic and magnetic signatures -- they could be sent ahead to conduct surveillance or prepare for an invasion without tipping off enemy forces. They can be small enough to be launched from almost any ship, sub or aircraft -- some are even light enough to be FedExed -- and thus can conduct missions in water too shallow for conventional craft. They can be produced relatively inexpensively, so they wouldn't need to be recovered in dangerous or inconvenient circumstances. They would act as "force multipliers," taking care of programmable tasks and freeing up manned warships to take on more complex ones. And they could be sent on the riskiest missions, to help keep sailors and Marines out of harm's way.