UUVs Will Foster Fundamental Change in Naval Warfare

Swarms of Mini-Vehicles Could Disable Enemy Mines Using Chemicals or Heat

By JAMES H. PATTON JR.

During the Afghanistan and Iraq conflicts, the cameras of the press often were focused on the successes of various unmanned aerial vehicles (UAVs)--most notably the Predator and the Global Hawk--that performed a number of intelligence, surveillance, and reconnaissance missions. The Predator also has been successfully employed as an unmanned attack aircraft. Not surprisingly, many have asked why there is not an analogous family of Unmanned Underwater Vehicles (UUVs) to achieve similar successes for U.S. forces underwater.

In fact, UUVs have been around about the same length of time. In World War II, the Germans employed both UUVs (in the form of homing torpedoes) and UAVs (as radio-controlled "glide bombs"). Somewhat later in the war, the Allies employed variants of each. In recent years, however, UAVs have truly "stolen a march" on UUVs, and now point the way toward the broad utilization of various types and sizes of unmanned vehicles in the underwater realm.

Given the technology already at hand, for example, it would not be difficult to create swarms of small mini-vehicles that could attach themselves to enemy mines, penetrate their casings by chemical or thermal means, and destroy them without tipping off the enemy that its mine field is being neutralized. For other missions, the U.S. Navy's Advanced SEAL Delivery System, a mini-submarine now in development as a transporter, could be adapted to perform a variety of surveillance and reconnaissance tasks.

Fundamental Change to Warfare

Many UUVs are in development, and their future use will bring fundamental change to underwater warfare. But any assessment of the future of UUVs must include an explanation of the vernacular. The acronym UUV implies a degree of autonomy or, at the least, some enhanced level of embedded "intelligence." As is true in the domain of unmanned aircraft, different UUVs are equipped with different systems that give them different capabilities. These include a subset of tethered craft, called remotely operated vehicles (ROVs), that receive power or send and receive information via their tethers. They comprise a large percentage of the UUVs now in operation or being considered for future development or production. A second subset, called autonomous underwater vehicles (AUVs), comprises craft that are indeed completely free of any direct physical control by human operators, ships, or airplanes.

Differences between the two subsets, or classes, of UUVs are not always clear. For example, a UUV such as the Mk48 ADCAP (Advanced Capability) torpedo can begin its brief underwater career as an ROV, receiving orders and sending back status reports via a thin wire or fiber optic link. When that link is broken or deliberately cut while the torpedo is en route to a target, it converts to an AUV, operating on stored or self-generated information. In this article, specific UUVs will be described either as ROVs or as AUVs, depending on whether they employ a physical tether.

If provided with a tether somewhat heavier than a wire or fiber optic data link, ROVs are freed from the significant engineering difficulties associated with the storage of large amounts of energy. They are capable of conducting some significantly heavy work on or near the ocean bottom or of functioning there effectively for extended periods of time. The civilian offshore oil industry has been the clear leader in the ROV field for decades, and remains a fertile source of commercial-off-the-shelf hardware and concepts for other applications. Few have not seen, for instance, the video footage of the Titanic or the Bismarck that was retrieved by commercial ROVs operated by Dr. Robert Ballard.

New roles and missions for submarines, coupled with technological advances that can be employed by ROVs, are creating fresh opportunities for improved intelligence and surveillance. Submarines, particularly the nuclear-powered ballistic-missile submarines (SSBNs), have long used ROV-like objects to provide assured (but very low data rate) reception of communications while on patrol. These buoy-like devices are sent to the surface and towed by the SSBNs, which remain in the depths. Today, the Navy is placing increased emphasis on the need for submarines to be more integrated with surface forces and, thus, able to take on a wider variety of roles and missions. This creates a need for better connectivity. Today's submarines have to both transmit and receive at high data rates while operating at high speeds and greater depths. For that reason, the Navy is investigating variants of the submariners' "legacy" towed buoy. Meanwhile, electro-optical and radio-frequency sensors are enjoying dramatic reductions in size and cost as performance improves geometrically.

British Look at Tethered Buoy

It is reasonable to assume that any mast or antenna that penetrates the ocean surface for communications purposes would be able to perform an additional role--for example, provide the manned platform below with a substantial degree of situational awareness in support of its intelligence, reconnaissance, and surveillance mission. The British are interested in an ROV called the Retrievable Tethered Optical Fiber (RTOF) buoy, which provides periodic communications windows of several minutes when allowed to float freely until the available tether line is fully deployed, at which time it is retrieved.

The covert detection and localization of sea mines in restricted waters looms as a critical submarine mission, given the wide acceptance of an operational plan in which the Navy is the "enabler" for the entry of follow-on joint forces, and the submarine is the early enabler for the rest of the Navy. To meet this requirement, the Navy has greatly improved its hull-mounted mine-detection sonars. In addition, submarine-deployed AUVs are being fielded to conduct mine-hunting tasks. The BLQ-11 Long-Term Mine Reconnaissance System (LMRS) has been developed in essentially the shape and form of a 21-inch heavyweight torpedo. With ahead-looking volume-search and side-scan bottom-search sonars, it can swath out a path more than a hundred miles long, either storing its findings until returning to the submarine or relaying them back via a radio frequency link. It is entirely feasible that a submarine could have several LMRSs aboard, enabling it to plot a route through the Straits of Hormuz in a few days.

Many of the UUVs in development or in the fleet are utilized and deployed by submarines. However, an AUV being developed for the surface Navy is, in a sense, an unmanned submarine. A major element of the WLD-1 Remote Minehunting System (RMS) is the Remote Minehunting Vehicle (RMV), a large (23 feet long, 4 feet in diameter) diesel-powered UUV deployable from a destroyer. It can snorkel for distances of more than 100 miles, depending on its assigned transit and search speeds. Like the LMRS, it is equipped with an organic ahead-looking search sonar (of a more advanced type than the LMRS), and carries an organic winch-deployable body--which the RMV tows at an appropriate depth to provide the side-scan feature used for the detection of bottom mines.

The RMV is currently controlled by a line-of-sight radio-frequency link to the mother ship that is also used for data extraction. Ultimately, it will be provided a satellite up/downlink capability, enabling any manned platforms having to stand far off from what could be a heavily defended area of interest. Given some additional stored energy, perhaps with rechargeable batteries in lieu of the towed side-scan sonar and associated winch, the RMV could snorkel close to the area of interest, then shut down, shift to the batteries, and conduct its mine-hunting mission a la LMRS--at depth with its own hull-mounted side-scan sonar. At the end of its search, or as needed, the RMV would come to communications depth and resume snorkeling. Fitted with appropriate sensors, like the submarine communications ROVs discussed above, the RMV would have a degree of situational awareness allowing it to dive for safety if threatened during its transit and snorkeling phases.

'The Crown Jewel' in the U.S. Arsenal

A Defense Science Board review of the U.S. submarine force in 1998 declared the submarine to be the "Crown Jewel" of the Defense Department. But it noted that the "tyranny of the 21-inch torpedo tube" in attack submarines greatly limits the potential contributions and capabilities of the submarine platform. There is no area where this limited access to the ocean environment is more constraining than submarine-launched UUVs. However, the Ohio-class ballistic-missile submarines (SSBNs) have tubes, designed for the Trident missile, more than seven feet in diameter. During the Giant Shadow experiment conducted last winter in Caribbean waters by the Ohio-class SSBN USS Florida, one of the many demonstrations carried out was the vertical launch and subsequent employment of the large (28 feet, 5 inches in length; 38 inches in diameter) experimental AUV Seahorse, developed by the University of Pennsylvania's Applied Physics Lab. The Seahorse missions included the successful detection and plotting of a practice minefield and the ferrying of supplies and information between the Florida and special operations forces deployed ashore as a part of the experiment. Even larger AUVs could have mission profiles measured in weeks rather than days or even hours, and conduct antisubmarine warfare or intelligence, surveillance, and reconnaissance missions in places where, for physical or political reasons, its mother ship could not operate.

Some of these large AUVs might be derivatives of existing manned platforms that already operate in an autonomous fashion. It is conceivable that units such as the Advanced Swimmer Delivery System (ASDS), a mini-submarine designed to transport Special Operations Forces, could be fitted with sensor arrays and inboard electronics optimized for intelligence and reconnaissance collection, fusion, and analysis with processed information injected into the "global grid."

There also are missions aplenty for tiny UUVs, some of which are already being developed. Experts have discussed at length the need to covertly determine, using UUVs, the extent and precise location of mines in a desired transit route. It is likely that a safe passage can be charted given this knowledge, but there will be times in which some small percentage of these mines will just be "in the way."

A Covert Neutralization

Thus, there is an equally important need to neutralize these mines selectively and covertly, preferably without causing a high-order detonation that would tip off the effort in progress and instigate reseeding of the mine field. Some mines can be manually disabled by special operations forces ferried by a large manned AUV such as the Advanced SEAL Delivery System. Another option is the development of small AUVs, 2 to 3 feet in length, that could swim, perhaps in swarms, a few miles to the mines, sense their presence, and attach themselves to the mine casings. There, they would await a command destruct signal. Or they could chemically or thermally penetrate the casings and either destroy them or disrupt their operation. Carried and launched by larger AUVs, these mini-AUVs could be staged into an area of interest. They could be created by adapting small expendable devices that already exist. One example is the Expendable Mobile Antisubmarine Warfare Training Target, which runs pre-programmed routes for many hours as it simulates the signatures of submarines in antisubmarine warfare training.

Another adaptation might fulfill a near-term requirement by submarines for periodic two-way communications windows. The existing Submarine-Launched One-Way Transmission (SLOT) buoys could be adapted to expendable ROVs carrying several miles of inexpensive fiber optic fiber. About the size of a sonobuoy, the SLOT buoy is an untethered device, carrying a tape-recorded message that is launched from a signal ejector.

The conceptual employment of UUVs has changed abruptly in recent years, heavily stimulated by a two-year Defense Advanced Research Projects Agency Submarine Payload and Sensors Program that was precipitated by the Defense Science Board study. However, there is much more to come. The embryonic program to convert four Ohio-class ballistic-missile submarines to guided-missile submarines (SSGNs) will provide the fleet with a quantum increase in total payload storage space and unprecedented access to the ocean environment. The Seawolf-class attack submarine Jimmy Carter (SSN 23) now under construction and future variants of the Virginia-class SSNs also will have much greater access and payload-storage options. For example, given better access to the ocean environment, these submarines, carrying large and powerful ROVs, could conceptually conduct underwater reloading and resupply from covertly placed forward weapon and stores caches.

In short, naval UUVs, deployed and utilized by both submarines and surface ships, are here to stay. They will span a large range of sizes and will contribute to missions not yet conceived--and very probably in ways not yet envisioned.n