SDVs carry a pilot, co-pilot, and combat swimmer team and their equipment to and from maritime mission objectives on land or at sea. The Pilot and co-pilot are often a part of the fighting team. The SDV has compressed air to extend the range of a swimmer's own air tank or rebreather.
The SDV is used primarily for covert or clandestine missions to denied access areas (either held by hostile forces or where military activity would draw notice and objection).
It should not be confused with the larger, dry submersible called the Advanced SEAL Delivery System (ASDS). The SDV is flooded, and the swimmers ride exposed to the water, breathing from the vehicle's compressed air supply or using their own SCUBA gear. (The ASDS is dry inside, with a full life support and air conditioning system.)
The SDV is lithium-ion battery powered and equipped with propulsion, navigation, communication, and life-support equipment. The Mk 8 Mod 1 SDV can deliver several fully equipped SEALs to the mission area, be "parked" or loiter in the area, retrieve the SEALs, and return home.
The Mark 8 Mod 1 SDV is currently the only SDV employed by US military. Other operational vehicles included the now retired MK 6, MK 7, and the Mk 11.
SDVs are generally launched from a Dry Deck Shelter on the back of a submarine, or from amphibious carriers (surface craft) equipped to launch and recover the SDV. It can also be air-dropped (unmanned) into an operational area from a C-130 Hercules.