The SEAL Delivery Vehicle (SDV) is a crewed submersible and a type of swimmer delivery vehicle used to deliver United States Navy SEALs and their equipment for special operations missions. It is also operated by the Royal Navy's Special Boat Service, which operates three SDVs. The SDV, which has been in continuous service since 1983, 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 is generally deployed from the Dry Deck Shelter on a specially-modified attack or ballistic missile submarines, although it can also be launched from surface ships or land. It has seen combat in the Gulf War, Iraq War, and the US intervention in Somalia. The SDV was intended to be replaced with the Advanced SEAL Delivery System (ASDS), a larger, dry submersible that is often confused with the SDV. 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, while the ASDS is dry inside and equipped with a full life support and air conditioning system. The ASDS was canceled in 2009 due to cost overruns and the loss of the prototype in a fire. The Navy currently plans to replace the SDV with the Shallow Water Combat Submersible (SWCS), which will be designated the Mark 11 SDV. The SWCS is expected to enter service in 2019. 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 invented by the Italians during World War I. The idea was successfully applied by the Italian Navy (Regia Marina) also early in World War II. The official Italian name for their craft was Siluro a Lenta Corsa (SLC or "Slow-running torpedo"). The vehicle was then copied by the British when they discovered the Italian operations and called it the "Sleeping Beauty" or Motorised Submersible Canoe. 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 American 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,