Diver-tugs, tow-behind, scooters The most common type of DPV tows the diver who holds onto handles on the
stern or
bow. Tow-behind scooters are most efficient by placing the diver parallel to and above the propeller wash. The diver wears a harness that includes a crotch-strap with a
D-ring on the front of the strap. The scooter is rigged with a tow leash that clips to the scooter with releasable metal snap.
Swimmer delivery vehicles SEAL Delivery Vehicle, an example of the wet type of Swimmer Delivery Vehicle. Swimmer Delivery Vehicles (SDVs) are wet subs designed to transport
frogmen from a combat swimmer unit or naval
Special Forces underwater, over long distances. SDVs carry a pilot, co-pilot/navigator, 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. An example of a modern SDV in use today is the
SEAL Delivery Vehicle used by the
United States Navy SEALs and British
Special Boat Service. For long-range missions, SDVs can carry their own onboard breathing gas supply to extend the range of the swimmer's scuba equipment. For extended missions on land, a team can be re-supplied by contact with other SDVs. In the latter usage, SDVs can stealthily plant mines and other bombs on ships or port infrastructure and then retreat to a safe distance before detonating the explosives. In addition to destroying targets, the SDV can mislead enemies as to where they are being attacked from.
Manned torpedoes These are torpedo or fish-shaped vehicles for one or more divers typically sitting astride them or in hollows inside. The
human torpedo was used to great effect by commando frogmen in
World War II, who were able to sink more than 100,000 tons worth of ships in the Mediterranean alone.
Wet subs As DPVs get bigger they gradually merge into
submarines. A
wet sub is a small submarine where the crew spaces are flooded at ambient pressure and the crew must wear diving gear. Covert military operations use wet subs to deliver and retrieve operators into harbors and near-shore undetected.
Towed sleds These are unpowered boards (usually rectangular) towed by a surface boat which function as
diving planes. The diver holds onto the sled and may use a quick-release tether to reduce fatigue. Depth control while submerged is by adjusting the angle of attack. Sometimes known as manta-boards, after the
manta ray. Towed sleds are useful for surveys and searches in good visibility in waters where there are not too many large obstacles. The route is largely controlled by the towing vessel, but the diver has a limited amount of control over vertical and lateral excursions. ==Modern DPVs==