Robot jellyfish? Eel-like craft? Why US Navy wants undersea drones.

Because the US Navy relies on stealth to carry out some of its most important national security operations, many such missions take place underwater, where submariners eavesdrop on the communications of adversaries and quietly position themselves for missile strikes should the need arise.

Now, the Navy is turning its attention to developing unmanned undersea vehicles, as the defense budget crunch threatens to curtail the operation of the costly submarine fleet. 

Just as Unmanned Aerial Vehicles (UAVs, or drones) have become ubiquitous in America’s land wars of the past decade, UUVs could help to transform the way the US military operates in the world’s oceans, experts say. To that end, the Navy is funding some highly experimental projects that sound as if they are pulled straight from science fiction films.

At university labs across the US, the Pentagon's Office of Naval Research (ONR) is bankrolling, for example, the creation of robotic jellyfish that mimic the efficient natural movements of the ocean creature and that could ultimately be useful in underwater surveillance and search-and-rescue missions. Such robots could also theoretically be powered by hydrogen and, therefore, never run out of fuel. 

ONR also funds projects to mimic the nearly wake-free undulations of the eel and the propulsion of the tuna, because engineers still have not been able to create underwater craft that swim as well as a basic fish.

“We’ve got a lot of great potential out there, and it’s starting to become quite tangible,” Adm. Jonathan Greenert, chief of naval operations and a member of the Joint Chiefs of Staff, said of UUVs in remarks at the American Enterprise Institute think tank in Washington last month.

Most of the unmanned crafts the Navy is developing are less exotic than robo-fish, but they are also much less pricey to build and maintain than America’s current fleet of nuclear-powered attack submarines.

“Our manned submarines, which are the keys to the realm right now, are extremely expensive,” says Bob Work, undersecretary of the Navy from 2009 to March 2013 and now chief executive officer of the Center for a New American Security (CNAS). “We can’t buy as many of them as we’d like.”

The budget calls for the Navy to maintain a fleet of 48 nuclear-powered attack submarines – "and that's pre-sequestration," notes Mr. Work, citing the across-the-board federal spending cuts that went into effect in March and that will shave another $498 billion off the defense budget in the new fiscal year unless Congress intervenes. Given the current fiscal environment, “It’s very difficult to even maintain 48 boats,” he adds – a level that's less than half the size of the nation's 100-sub fleet during the cold war.

The fiscal reality means the Navy’s submarine fleet is likely to shrink to the low 40s and 30s into late 2020 and 2030 “because we didn’t build as many manned submarines in the 1990s as we wanted, and therefore the retirements of nuclear-powered attack [subs] will exceed the number being commissioned,” Work says.

At the same time, attack ships on the surface are becoming more vulnerable because advanced guided weapons – including anti-ship ballistic missiles, stealthy supersonic missiles, and wake-homing torpedoes – are proliferating. This vulnerability “makes you more keen to do things underwater, but you can’t buy as many manned subs, so UUVs will be a means by which the US will be able to maintain its undersea dominance even with a smaller number of manned submarines,” Work adds.

There are reasons UUVs haven’t caught on so far, however. One key roadblock to their development and widespread use has been communications. 

“It’s literally easier to communicate with the Mars rover than it is to communicate with a UUV at 100 nautical miles under water,” Work says.

Radio waves don’t travel well under water, so UUVs must surface and extend antennae to transmit data. As a result, “just communicating with a UUV is very difficult,” he adds. 

For this reason, too, time lags under water are measured “in days and weeks,” says Alan Beam, a 26-year veteran Navy nuclear submariner and the former program manager for Unmanned Underwater Vehicles at the Pentagon’s futuristic Defense Advanced Research Projects Agency (DARPA).

“If you want to talk to UUVs on a near-real-time basis, you have to establish a communications path,” adds Mr. Beam, who now runs the Autonomous Undersea Vehicle Applications Center, which advocates the development of UUVs in both the defense and commercial sectors.

While it’s possible to put sensors and weapons on UUVs, up to this point the underwater vehicles "didn’t have the endurance to be tactically useful,” he notes. 

Once the Navy can commission a UUV that can go out for 30 days at a time, “then you’re really starting to get something.”

To do that, the Navy needs bigger UUVs that can store fuel. It refers to these as “large diameter UUVs,” and the goal is ultimately to be able to send them out for at least two months.

These programs “are funded, and funded fairly heavily,” Beam adds.

Still, their current funding is a fraction of that for unmanned aerial vehicles. The Pentagon has budgeted a bit more than $1 billion for all unmanned maritime systems, about half of which will go to unmanned underwater vehicles. By comparison, the Pentagon plans to spend more than $45 billion on UAVs in the next year, according to figures from the Association for Unmanned Vehicle Systems International.

Even so, the trend line for UUVs “is very, very bright,” says Work of CNAS. In the future, he notes, large UUVs might work in the same way as all-purpose trucks, able to carry mines and torpedoes as well as to transport Special Operations Forces.

Smaller UUVs might also be implanted with sensors and weapons, sit off the coast of an enemy harbor, “and essentially be a mobile minefield with small torpedoes so when ships come out of the harbor they could disable them.”

For now, antimine UUVs are already “going like gangbusters,” being deployed extensively in places like the Persian Gulf to sweep for mines using programmed GPS coordinates, Work adds. 

UUVs can sweep areas with relative precision, but “what they are working on right now is the false-alarm rates, because the sonars they carry are very small.” 

In years to come, UUVs are not likely to replace manned nuclear-powered attack submarines. They are not fast enough to follow – or advanced enough to hunt and track – adversaries' submarines, for example. 

They will, however, probably be designed to “do the missions that are dull, dangerous, dirty, or deceptive that the [nuclear-powered attack submarines] can’t do,” Rear Adm. Richard Breckenridge, director of the Navy’s Undersea Warfare Division, told lawmakers at a September congressional hearing. “So what we’ll do is we’ll be able to free up those manned assets to go do our nation’s bidding.”