You don’t have to walk through the doors of the Submarine Force Museum to begin your experience. Outside you are met with several large artifacts that allow the visitor to quickly jump right into Submarine and Naval history. For instance, outside of its doors, hung towards the sky are the hull rings of the Holland and Ohio class submarines. These give the visitor a taste of how far submarine development has come from 1900 to now. A recent addition is the NR-1 whose bright orange paint can’t be missed. But alongside these large representations of submarine history is a smaller vehicle. It can be passed right over due to its size but plays a key role in military missions, many of which are still kept top secret today. The Swimmer Delivery Vehicle or SDV is used on clandestine operations by a group that is shrouded in mystery just as much as the Silent Service.

SDV in front of Submarine Force Museum.
Picture Credit: Erica Ciallela

Looking inside the SDV from above. at the Submarine Force Museum.
Photo Credit: Erica Ciallela

The U.S Navy Seals are a volunteer unit, just like the Submarine Force. Part of the U.S. Navy’s Naval Special Warfare Command, the number of Seals is small when compared with other forces. Officially established in 1962 by President John F. Kennedy, Seals stands for Sea, Air and Land, the fronts that any seal member must be prepared for on any given mission. Today’s SEALS find their heritage dates back to five groups that played large roles in World War II and the Korean War. These groups were the Army Scouts and Navy Raiders; Naval Combat Demolition Units, Office of Strategic Services Operational Swimmers, Navy Underwater Demolition Teams, and the Motor Torpedo Boat Squadrons. These groups were used in missions that included reconnaissance, explosive destruction of underwater obstacles, and marking mines for minesweepers. During their time, they made advancements in closed-circuit diving, underwater demolitions, and mini-submarine operations. While established by Kennedy, the modern SEALSs come from a long evolutionary line of forces that shaped the group to its current state. Today’s SEAL teams spend much of their time getting as close to the enemy as possible without being detected. This calls for special equipment that not just any team can have. Enter the SDV. Today’s submarines are large enough to cover entire football fields. And while they are extremely quiet and are great at remaining hidden, there are just some jobs that require a much smaller vehicle. The SDV allows Navy SEALs to exit a submarine and get up close to an enemy.
According to the Navy SEAL Museum, the purpose and need for SDV’s was explained in a 1952 report titled “Underwater Swimmers.” It stated that “Whenever it is necessary to operate near an enemy-held shore in as complete secrecy as possible, the approach to the object must be made under water. The first part of the approach can be made in a fleet-type submarine, but these 1500-ton vessels cannot operate submerged in water shallower than 60 feet, and depths less than 150 feet are considered hazardous. The final submerged approach must be made by swimming or in a small submersible. On many coasts throughout the world, depths less than 60 feet extend out several miles from shore. In these areas even, men equipped with SCUBA would not have enough breathing gas to swim the distance and return. Moreover, they would be seriously fatigued when they reached their objective after their swim of several hours. To supplement their swimming, they must have a small, powered submersible.” The SDV is a manned submersible that allows Navy SEALS to execute their missions. The submersibles are free-flooding which means that the unit is filled with water during the whole mission. Team members breathe compressed air from an internal life-support system or from Scuba equipment. The predecessor to the SDV was developed by the British during World War II. This original design, while used in training and exercise, never saw combat. It could only carry one crew member and its military potential was minimal. However, a similar concept would be used to help create the design for today’s SDV’s. Out of the approximately 2600 active-duty SEALs, only around 230 are qualified to operate or serve on SDV missions. Besides being filled with water, the vessels have no windows. Navigation is done through sonar. Having to work in tight conditions and extremely cold temperatures, only a few SEALs are qualified to handle these circumstances.
Officially commissioned in 1983, the first modern SDV was the MK 7. There were six different models of this type, each one changing and adapting as new upgrades were found. This first design could carry a pilot and three additional crew members. The instruments and battery compartments were kept in water-tight compartments that were pressure-proofed to deal with variable depths. The early models were operated with an electric motor, powered by a rechargeable silver-zinc battery. The first model began experimental service in 1967 and had its first mission in 1972.

A Mk VIII Mod 1 minisub operated by members of a SEAL Delivery Vehicle Team maneuvers into a dry dock shelter fitted to USS KAMEHAMEHA (SSN-642), a U.S. Navy submarine.
U.S. Navy photo by Chief Photographer’s Mate Andrew McKaskle
http://www.americanspecialops.com/navy-seals/seal-delivery-vehicle-teams/

Following the MK7, the MK8 and MK 9 made electrical improvements but since the beginning, the design has mainly stayed the same. Today’s SDV’s run on lithium-ion batteries and utilize state-of-the-art navigation systems. Newer models carry a crew of six. The SDV is a clear example of how each unit within the military depends on each other to accomplish its missions. We may joke about being surface or submariner or Army or Navy, but each branch plays a vital role and are intertwined, just like the SDV and the submarine.

SEAL divers from SEAL Delivery Vehicle Team Two (SDVT-2) getting ready to launch a Mk VIII Mod 1 SDV minisub from the back of Los Angeles-class attack submarine USS Philadelphia (SSN 690).
image sourced from public domain | U.S. Navy photo by Chief Photographer’s Mate Andrew McKaskle
http://www.americanspecialops.com/photos/navy-seals/seals-sdv.php