What is an SDV? SDVs (SEAL Delivery Vehicles) are employed by U.S. Navy SEAL operators. They are small free-flooding submersibles that can transport up to six combat-equipped SEALs. Free-flooding means that the SEALs are surrounded by sea water during the entire mission, where they breathe compressed air from the SDV’s internal life-support system or from tactical underwater breathing apparatus. The SEAL Delivery Vehicle (SDV) is also operated by the Royal Navy’s Special Boat Service who operates 3 SDV’s.
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.)
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 silver zinc 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. 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 airdropped (unmanned) into an operational area from a C-130 Hercules.
The Mark 8 Mod 1 SDV is currently the only SDV employed by US military and Royal Navy, and it is an upgrade of earlier Mark 8 Mod 0 SDV. The primary improvement of Mod 1 over Mod 0 is that the former is constructed of aluminium alloy while the latter is built of glass fiber reinforced plastic. Mod 1 also incorporated advanced electronics. In addition to surface ship and submarine, other platforms the Mk 8 SDV can be deployed from include CH-47 Chinook & CH-53E Super Stallion helicopters. Other operational vehicles included the now retired MK 6, MK 7, and the Mk 11. The Special Boat Service of the United Kingdom Special Forces operates three Mk8 Mod 1 vehicles.