SEAPOWER Magazine The Official Publication of the Navy League of the United States VOL. 49, NUMBER 2 February 2006

16 Gliders: Under the Sea…

Small and autonomous, new underwater vehicles will enable the Navy to forecast ocean conditions, help pinpoint quiet diesel subs

By OTTO KREISHER, Special Correspondent

In the search for greater capabilities to counter the growing threat of quiet diesel submarines in littoral waters, the Navy is exploiting technology developed in concert with the nation’s leading oceanographic research institutions with financial support from the Office of Naval Research (ONR).

This potential antisubmarine tool is a relatively low-cost, long-endurance sensor capable of providing valuable data on water conditions such as temperature, salinity, pressure and turbidity, over large stretches of ocean.

The devices, called gliders, are small, autonomous underwater vehicles that look like short torpedoes with wings and tails. The current models have no external propulsion and very few moving parts. As a result, they are able to operate on battery power for extended periods to survey thousands of miles of ocean and report the data they collect.

Navy officials recognize that knowledge of those ocean conditions can allow more accurate predictions of the effectiveness of sonar and other antisubmarine sensors. That information also could be helpful in countering sea mines and in forecasting the operating environment for SEALs or amphibious raiders, the experts said.

In the future, the gliders also could become part of mobile sensor networks able to detect and accurately locate submarines in shallow, noisy littoral waters.

The idea for these undersea explorers was conceived about 15 years ago at Woods Hole Oceanographic Institution, Woods Hole, Mass. The concept has been developed and tested by that institution, the Scripps Institution of Oceanography in San Diego, the University of Washington and Webb Research of Falmouth, Mass.

Recognizing the potential value of these sensors for the Navy, ONR has supported the effort from the start and is continuing to fund advanced research.

Navy personnel tested all three of the current models of gliders and used them in exercises, including RimPac 04, a warfare exercise conducted in July 2004 in Hawaiian waters by ships of seven nations, including Australia, South Korea, Chile and the United States.

Although usually launched from surface vessels, a glider was successfully launched Nov. 14, 2005, with the help of Navy divers, from a dry deck shelter on the attack submarine USS Buffalo near Hawaii. Lt. Cmdr. Patrick Cross, force oceanographer at Submarine Force Pacific, said another test is expected in the near future in which a submarine deploys and recovers a glider.

The gliders all work basically the same way, Cross said. They are made to be nearly neutrally buoyant and are propelled by making changes to their buoyancy by moving small amounts of fluid into or out of their hull.

Moving the fluid internally is enough to make a 6-foot-long glider negatively buoyant, which causes it to sink slowly. Its 4-foot wings then develop lift, pushing the vehicle forward. When a glider reaches its prescribed depth — currently about 3,300 feet maximum — it expels the fluid to become positively buoyant and climbs back to the surface.

The current models advance on a preset course quite slowly, about 12 nautical miles a day. During the glider’s up-and-down voyage, sensors onboard record information about ocean conditions that is transmitted by Iridium satellite links when the vehicle reaches the surface.

For the Navy, the information goes into the Modular Ocean Data Assimilation System, run by the Naval Oceanography Office, which is available to submariners and antisubmarine warfare (ASW) forces.

While on the surface, the glider also can check its position with the Global Positioning System and get instruction on where to go next. Because it uses very little electrical power, the glider can run for weeks or months, depending on the type of batteries it carries, Cross said.

The gliders provide a capability long sought by the scientific oceanographic community and the Navy: A cheap means to spend a lot of time collecting a lot of data about the oceans, Cross said.

“In oceanography, one of the things we suffer from is not enough data on what the ocean is actually doing. These things provide a great source of just persistent data,” he said. “That’s sort of the goal, to be able to predict the ocean the way we predict the atmosphere.”

A glider developed by Scripps, called Spray, became the first autonomous underwater vehicle to cross the Gulf Stream underwater.

Dr. Russ Davis, a Scripps oceanographer, said the gliders will be used together with widely spaced hydrographic sensors, called floats, in an international experiment to keep track of ocean conditions all over the globe. The gliders would span the gaps between the floats and help provide vital details on changes in currents, temperature and other ocean conditions. The advantage of the gliders, he said, is that “they can be out there for a long period of time at relatively low cost, making measurements that wouldn’t be made otherwise.”

For the Navy, Cross added, “if we understand the ocean well, we understand how acoustic energy propagates through the ocean,” which is vital for ASW operations.

Thomas Swean, program manager for ocean engineering and marine systems at ONR, said the evidence is clear that military operations depending on underwater sensors are much more efficient if the environment in which they will work is known. That kind of information is increasingly important with the growing focus on quieter diesel-electric subs in the near-shore waters.

“One of the things that we’re concerned about, because of the technological advancements over the last 20 years, [is that] potentially hostile forces have very quiet submarines,” Swean said.

“Where, at one time, the U.S. Navy could feel fairly confident that it knew where most of the strategic submarines were, through our sensor systems, we no longer have that confidence, especially with diesel submarines in littoral areas,” he said.

The gliders can help improve that situation and are much cheaper to operate for extended periods than other hydrographic sensors, Swean said.

He said the Navy also plans to use gliders as part of a distributed network of persistent sensors that could be deployed over large areas of littoral waters as “sentries” to detect the presence of submarines. The next step is to develop technology that would make them able to positively identify a sub and track it well enough to allow an attack if necessary.

“That is pretty much the challenge. But the glider technology is playing a huge role in developing and proving a concept to be able to do that,” Swean said.

Although gliders still are in research and development, the Naval Oceanographer’s office plans to buy some and has requested proposals from the contractors, a spokesman said.

Meanwhile, ONR is supporting Scripps and University of Washington in developing a more capable glider that will be tested this year, Swean said.

This glider, called Liberdade, is shaped like a flying wing with a 20-foot wingspan. It can carry a considerable sensor payload, including hydrophone arrays that could detect and locate acoustic sources in the ocean, he said. It also could have magnetic anomaly detectors, which also can find submarines.

Because of its size and shape, Liberdade is much faster than the current gliders, with a cruise speed of 3 to 5 knots and a “burst speed” of more than 10 knots, he said.