SDV units in great demand as speed, range improve

Sea Power, Jul 2003 by Klose, John P

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.