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USS Greeneville with the ASDS attached.

Advanced SEAL Delivery System (ASDS) is a midget submarine operated by the United States Navy and SOCOM, designed to provide stealthy submerged transportation for special forces, primarily U.S. Navy SEALs, from the decks of nuclear submarines.

The ASDS is some 65 feet (20 meters) long, displaces about 70 tons, and is operated by a crew of two. Lithium ion battery propelled, it has a range of about 200 kilometers, a top speed of some 7.5 knots (14 kilometers an hour) and an operating depth of greater than 200 feet (61 meters). It can carry up to 14 passengers with little equipment or eight with a standard load-out of dive gear and weapons in a dry transportation chamber. It can lock out divers at depth and recover them using a separate Lock-In-Out (LIO) chamber. It is equipped with passive and active sonar, a radio mast, and a photonics mast.

Smaller swimmer propulsion devices such as the STD (Swimmer Transport Device) may be carried internally (basically smaller scooters), and small Combat Rubberized Raiding Craft (CRRC) or Inflatable Boat-Small (IBS) may be stored internally. However, such craft cannot carry gasoline engines due to safety issues on submarines and fuel issues in small spaces, and therefore have to be paddled or use small electric motors. Semi-rigid and rigid hull craft such as the zodiac cannot be accommodated.

ASDS was conceived to address the need for long range covert/clandestine insertion of Special Operations Forces. Previous mini-subs were of the wet variety, exposing Combat Swimmers to long, cold waits during transit that impeded combat readiness on arrival, and had limited blind underwater navigational capability. The first study to define ASDS was performed in 1983. Competitive conceptual designs were developed in the late 1980s, and the first contract for design and construction of the ASDS was awarded in 1994.

Funding was provided via Congressional line item to the Special Operations Command. The Navy Deep Submergence Office was selected as the technical design agent and program office. Technical assistance was provided by the Navy Experimental Dive Unit, Panama City; the Naval Special Warfare Command, Coronado; Naval Special Warfare Swimmer Delivery Vehicle Team 2, Norfolk; and the Special Operations Command (SOCOM) Special Operations and Acquisition Logistics (SOAL), Tampa.

Construction of the first ASDS was started in 1996 at a government estimated cost of US$160 million, to a low bid of $69 million. It was delivered in 2000 and cost US$300 million to develop. Subsequent submarines are estimated to cost $125 million a copy. Five more are planned, but production of the second system was placed on indefinite hold in December 2005 pending a production and cost review, and the resolution of many reliability problems. In April of 2006, the program for new submarines was cancelled and Northrop Grumman notified of termination. The current submarine is still in development and use.

• Swimmer Delivery Vehicle

History - SDV program.

The SDV program dates back to World War II and various sleds and vehicles developed for use by the Underwater Demolition Teams. After the war development continued in a garage-shop fashion by various UDT units, and included various "Marks" as the MK V, VII, 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 erroniously designated as the SEAL Delivery Vehicle after the Swimmer Deliver Vehicle Teams were renamed SEAL Deliver 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.