SEAL Delivery Vehicle The SEAL Delivery Vehicle or ( SDV ) is a manned submersible and a type of Swimmer Delivery Vehicle used to deliver United States Navy SEALs and their equipment for special operations missions and 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 . ) History . The SDV program dates back to World War II . Initiated by the Office of Strategic Services Maritime Unit ( OSS MU ) . A “ submersible canoe ” was developed by the British during World War II and called the “ Sleeping Beauty . ” It was employed by OSS MU during extensive training and exercises , but was never actually deployed for combat operations . The same capability was adopted by the post - war Underwater Demolition Teams ( UDTs ) in 1947 . The one - man submersible displayed little functional military potential ; however , it substantiated and characterized the need for improved and expanded UDT capabilities . After the war , development continued in a garage - shop fashion by various UDT units , and included various " Marks " as the MK V , VI , VII , and XII . Intermediate numbers were assigned to some vehicles that never made it off the shop floor . All were of flooded design . The wet vehicle SDV program ( officially named the Swimmer Delivery Vehicle , sometimes erroneously designated as the SEAL Delivery Vehicle after the Swimmer Delivery Vehicle Teams were renamed SEAL Delivery Vehicle Teams ) currently centers on the MK VIII MOD 1 , was first established in 1975 for use among UDT / SEAL teams . The early MK8 MOD 0 SDVs had a PRC104 UHF ultra high frequency radio for use underway . The newer model MK8 MOD1 has a dual sliding canopy and quick release hatch . Design . 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 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 . 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 airdrop ped ( unmanned ) into an operational area from a C - 130 Hercules . Mark 8 SDV . The Mark 8 Mod 1 SDV is currently the only SDV employed by US military , 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 platform Mk 8 SDV can be deployed from also includes CH - 47 Chinook & CH - 53E Super Stallion helicopters . Specifications : 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 .