The SEAL Delivery Vehicle (SDV) MK VIII was developed in 1975 by United States UDT (Underwater Demolition Team) / SEAL (SEa, Air and Land) teams as a reusable, submersible underwater vehicle. US Navy SEALs are essentially the grandsons of the World War 2 underwater demolition teams charged with blowing up underwater beach obstructions and performing vital shore terrain scouting before assaults by the regular land forces. UDT teams of those days had problems of limited compressed air time and swimming stamina when launched from their PT boats or submarines, having to make their way to the beach and find their way back out to sea. This method of operation reduced mission times and limited the operations of this critical component to American battlefield supremacy. As such, the SDV was ultimately developed.
As a submersible underwater vehicle, the SDV can carry SEALs and their equipment, increasing mission time while the swimmers personal energy level is maintained for the operation ahead. The SEAL Team pilot, co-pilot and passengers are situated in fully-flooded compartments and use their own individual Self-Contained Underwater Breathing Apparatus (SCUBA) during the mission. Operational scenarios for these SEALs can include underwater reconnaissance and surveillance, beach and surf observation and combat swimmer attacks.
Any Attack Submarine can be adapted to carry the ubiquitous SDV. The Dry Dock Shelter (DDS) is attached to the deck of the submarine (behind the sail) and is fitted so the submarine's weapon or sensor operations are not limited or affected in any way. The DDS is portable and can be air-lifted to its preset location and installed in 12 hours.
The SDV itself is propelled by an electric propulsion system powered by rechargeable silver-zinc batteries. Trouble with the batteries was experienced on long missions so the battery size was increased to compensate. The round nose shaped SDV maintains buoyancy and pitch attitude by the pilot using ballast and trim controls in the cockpit. For controlling the vertical and horizontal angles of the vehicle, the pilot has a joystick control that operates the forward bow planes and the aft rudder and elevator. The mini instrument panel supports Doppler navigation sonar that indicates speed, heading, depth and distance traveled. The electronic instruments are sealed within watertight compartments and have been designed for easy removal/replacement.
Seal graduates who are assigned to SDV School in Coronado, California, spend some three months in training and, upon completion, are then assigned to SEAL Team One in Hawaii or SEAL Team Two in Little Creek, Virginia. The course concentrates on diving and navigating the MK-VIII SDV in a variety of conditions and scenarios. As operation of this craft can be quite dangerous and technical - with the lives of the crew and SEAL Team at stake - it takes a good amount of time to effectively pilot the SDV to fullest potential. Though many are expelled from the course, heroic reputations can be made if a SEAL SDV trainee can graduate as a skilled pilot. Despite its Cold War legacy, details of the SDV training program itself naturally remain a guarded secret.
Such is the trademark of the US Navy SEALs.