Swimmer Delivery Vehicles (SDVs) (also called diver propulsion vehicles) are midget submersibles designed to transport frogmen from a combat swimmer unit or naval Special Forces underwater, over long distances. 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 swimmer team.
For long-range missions, SDVs can carry their own onboard compressed air supply to extend the range of a swimmer's own air tank or rebreather equipment.
There are two kinds. The "wet" type, where combat swimmers ride on the outside, exposed to the water. Examples of wet SDVs include the American "SEAL Delivery Vehicle".
There is also the "dry" type, where swimmers ride in a compartment inside, not exposed to the water. Examples include the American "Advanced SEAL Delivery System".
SDVs are used in maritime missions such as infiltrating combat swimmers into an enemy port or planting limpet mines on the hull of target vessels. They are also used to land a combat swimmer team covertly on a hostile shore in order to conduct missions on land. After completing their mission, the team may return to the SDV to exfiltrate back to the mother-ship.
For extended missions on land, a team can be re-supplied by contact with other SDVs.
The origins of the SDV stems from the Motorised Submersible Canoe created during World War II.