SDV Units in Great Demand as Speed, Range Improve

By JOHN P. KLOSE

The Navy's swimmer delivery vehicle (SDV) platoons are some of the highest-priority and least-available units of America's military forces. They were in high demand in several combatant commands, such as the European Command, even before the war on terrorism began. Prior to the 9/11 terrorist attacks, for example, the Central Command assigned its deployed SDV Task Unit to conduct reconnaissance and surveillance for maritime interdiction operations against Iraqi oil smuggling, to train foreign combat swimmers, and to perform critical short-notice, low-visibility missions.

Each platoon comprises 11 Navy SEALs, a diving medical technician, four maintenance technicians, and two swimmer delivery vehicles, or mini-submarines that are launched from fast attack submarines or other ships and can clandestinely transport a squad of SEALs on a wide variety of missions.

A Rich History

The SDV platoons are part of a rich and historic past shared by submarines and naval combat swimmers. Italian and British naval commandos riding submarine-launched underwater craft conducted some of the most daring maritime raids of World War II. The ability to attack ships and move clandestine forces through dark waters under the cover of night was proven to be a key military capability with a strategic value that far exceeded its cost.

Since World War II, U.S. naval special warfare has steadily developed its own mobility for undersea operations and is now a world leader in the field. The U.S. Navy's underwater demolition teams began operating from diesel submarines in World War II and Korea, but they moved from ships to shore either by inflatable boat or by swimming.

In the early 1950s, underwater demolition teams began working with foreign-built mini-subs. These free-flooding or wet mini-subs were often nothing more than torpedo-like devices that two or three combat swimmers sat astride.

A Greater Emphasis

During the Vietnam War, several Korean-era diesel submarines were recommissioned and configured to carry and deploy SDVs along with underwater demolition team and SEAL team members. These submarines had previously carried Regulus surface-to-surface missiles stored in large bow-mounted hangers, which were modified to transport and launch SDVs and to lock combat swimmers into and out of the submarine. These vessels were decommissioned after Vietnam, with the exception of the USS Grayback, which continued into the 1980s as the Navy's dedicated platform for combat swimmer operations.

In the 1970s and early 1980s, naval laboratories designed and built wet SDVs. Steady improvements in propulsion, battery technology, and navigation electronics resulted in the design of the Mk8 Mod 0 SDV, a craft that could deliver a squad of SEALs over moderate distances. By the late 1970s, a second SDV configuration, the Mk9, was developed to add an effective standoff ship-attack capability.

A significant factor in the development of today's SDV was that of the operators. For the SEALs, working with SDVs was, and remains, a very cold life. For most mission profiles, the boats were capable of completing the mission, but the men inside were pushed to the limits of human endurance. Also, funding constraints prevented the SDV from evolving into a full operational capability and, as in so many cases in the post-Vietnam era, adequate resources were not available for maintenance, component upgrade, or training. Naval special warfare had an operational capability, but it was one that required significant grooming before becoming mission ready.

An Exciting New Era

A turning point in undersea mobility came with the development of a concept to mate a portable SDV shelter with a fast attack submarine. Mounted on the hull of a submarine, the new shelter enabled a submerged attack submarine to transport, launch, and recover SEALs with their SDVs or combat rubber raiding craft. A "fly-away" concept, similar to that used for deep submergence rescue submarines, is employed to airlift this shelter, its associated personnel, and the SDV to almost any location in the world.

The deck shelter quickly evolved into today's dry deck shelter. Built by General Dynamics' Electric Boat Division, Groton, Conn., the first dry deck shelter was fitted to the USS Cavalla (SSN 684), which was configured to accept it in 1982. After successful sea trials, developmental tests, and operational demonstrations, the dry deck shelter was approved for service use and operationally deployed in 1983. The dry deck shelter fits on the hull of a submarine aft of the sail. It is linked to the middle hatch to provide SDV team members with the freedom to move between the dry deck shelter and the submarine while the submarine is underway. The dry deck shelter is 38 feet long, 9 feet wide and comprises three compartments, one of which houses an SDV or up to 20 SEALS. The other compartments contain a hyperbaric chamber where divers occasionally may be required to decompress, and a transfer trunk that sits above the submarine hatch and is used by divers to move between the submarine and the other two compartments.

One advantage of the dry deck shelter is that SEALS and others can remain warm and dry almost up to the moment of launch.

With the advent of the dry deck shelter, the USS Grayback was decommissioned in June 1984. Five additional Permit-class long-hull submarines, four former fleet ballistic-missile submarines, and five Los Angeles-class submarines were eventually modified to carry the dry deck shelter. During the same period, five additional dry deck shelters were delivered to the Navy.

New Capabilities Desired

The integration of the fast attack submarine, the dry deck shelter, and the SDV created a significant new capability for naval special warfare. The nuclear-powered submarine equipped with a dry deck shelter was a sustainable asset with global reach. SEALs and SDVs could be delivered almost anywhere.

This quantum improvement in capability led to further changes in the hardware and structure of SDV platoons.

First, underwater demolition teams were reorganized into SEAL and SDV teams in May 1983. The new SDV teams were tasked with developing standard operating procedures and tactics for the SDV. This led to a complete mission analysis of SDV operations that now included the fast attack submarine and the dry deck shelters, as well as other delivery capabilities. Specific mission targets and host platform considerations were analyzed to establish the baseline for SDV technical requirements.

The limited-range SDVs of that era required close-in, shallow-water delivery, which increased the risk of submarine detection and grounding. Thus, it was obvious that an SDV with "longer legs" was needed to lower overall mission risks and reach more maritime targets.

Second, advances in propulsion, electronics, sonar, and battery technology allowed engineers to greatly expand the capabilities of the SDV. Even relatively unsophisticated improvements in fiberglass fabrication, power control, design analysis software, and sound-muffling techniques contributed to this expansion.

Finally, life-cycle sustainment costs for the overall program were increasing at an unacceptable rate. This was largely the result of a program that was expected to maintain both the Mk8 Mod 0 and Mk9 SDVs. These two entirely different SDVs lacked common components. There were additional program costs caused by sole-source suppliers, flawed reliability designs, and stove-piped logistics support.

The "Gator" Class SDV

These factors provided the impetus for developing a completely new SDV. Formal acquisition efforts to design and build this craft began 1988. The resultant Mk8 Mod 1 SDV would replace both the Mk8 Mod 0 and Mk9 boats.

The Coastal Systems Station in Panama City, Fla., was charged with designing and building this new boat. SDV operators and station scientists, engineers, and technicians combined their unique expertise in underwater mobility and technology to produce a truly remarkable craft.

The first Mk8 Mod 1 SDV was completed in July of 1995 and passed its operational assessment with flying colors. This new craft was designed to reflect the same basic size and displacement of its predecessor, the Mk8 Mod 0 SDV, in order to fit within the existing dry deck shelter. Inside the aluminum skin, however, was an ingenious array of ballast and trim systems, navigation and communication systems, propulsion and power systems, compressed air systems, and more-spacious cargo and passenger compartments.

Not only did the new SDV travel twice as far and 50 percent faster than the previous version, it was quieter and significantly easier and less expensive to maintain. Overhauls were shortened from nine months to five weeks in duration and their frequency reduced from every two years to every four years. In addition, life-cycle-support experts at the Coastal Systems Station developed a system of logistics, configuration management, training, and documentation for the program that is recognized as one of the best life-cycle sustainment systems in the Navy.

The new Mk8 Mod 1 SDV was formally designated the Gator-class SDV in 1996 in honor of the late James "Gator" Parks, a Coastal Systems Station engineer and retired SEAL who dedicated his career to SDVs and the men who operate them. His leadership, ingenuity, and, sometimes, downright stubbornness led to the creation of the Mk8 Mod 0 and Mk9 SDVs as well as the new Mk8 Mod 1 boat.

The Operational Impact

Naval special warfare's SDV program has matured into perhaps the most formidable swimmer delivery capability in the world. The SDV's technical specifications, operational capability and flexibility, and cost-effective price tag make it one of the world's top performers. Even the famed British Special Boat Squadron (SBS), whose naval commandos were some of the first true underwater warriors, has procured the Mk8 Mod 1 boat through the Foreign Military Sales (FMS) program.

From the SEALs' perspective, the true value of the Mk8 Mod 1 SDV is its operational capability. SEALs now have a sophisticated and reliable vehicle capable of delivering them to target areas around the globe. Naval special warfare forces are fully prepared to conduct the full range of maritime special operations, to include beach-reconnaissance, intelligence-gathering, and direct-action missions.

The Mk8 Mod 1 SDV can be deployed from a variety of special operations and conventional surface vessels and aircraft. This greater flexibility increases the operational commander's ability to quickly employ an SDV without waiting for the arrival of modified fast attack submarines.

A Bright Future

The Navy's reduction of the submarine fleet during the 1990s resulted in the loss of some submarines capable of carrying the dry deck shelter. However, several Los Angeles-class submarines have been modified to carry the shelter. The Seawolf-class attack submarine Jimmy Carter and all Virginia-class submarines also will be able to transport the dry deck shelter. In addition, four Ohio-class ballistic-missile submarines are being converted to guided-missile submarines (SSGNs) with the capability to support expanded missions by special operations forces. The SSGNs will carry both the dry deck shelter and the new Advanced SEAL Delivery System now (ASDS) under development.

The ASDS is a dry, one-atmosphere submersible that can transport a SEAL squad to a target area from either a surface ship or submarine. It has a lockout chamber that allows SEALs to stay warm and dry until they leave the vessel. The ASDS will improve the Navy's underwater mobility by performing in situations in which either the water is too cold or the transit is too long for divers operating in a wet boat. The ASDS is conducting its operational evaluation in Hawaii this summer and should be approved for service use later in the year.

New submersibles, new host platforms, and new missions are combining to meet the challenges of Sea Power 21, the new naval strategy issued in October by Chief of Naval Operations Adm. Vern Clark. Both the submarine service and naval special warfare community are poised to deliver the innovative concepts, technologies, and teamwork required to project direct and decisive power around the globe. *

Cdr. John P. Klose is a submarine officer and project engineer at the Coastal Systems Station in Panama City, Fla. He served as weapons officer onboard USS Cavalla (SSN 684) during the installation and testing of the first dry deck shelter. He recently spent three years on active duty with Special Operations Command, Central (SOCCENT) in Tampa, Fla.