![]() ![]() The UK’s possession of this difficult-to-counter capability is an important deterrent to potential adversaries, some of who may also have similar capabilities. In a more aggressive role, they can deliver small teams to attack targets or destroy shipping in harbours. The SBS can covertly infiltrate coastlines to plant sensors, gather intelligence, deliver and recover agents or extract persons of interest. Primarily used by the SBS (Special Boat Service), the SDV allows the very high-value nuclear submarine to stay further away from the coast and reduce the risk of detection. Carried underwater for thousands of miles, SF operators may be landed on a foreign shore, complete their mission and return undetected. Using submarines for inserting commandos is nothing new but the DDS and SDV gives the UK an important increase in maritime SF reach. ![]() HMS Artful seen with Dry Deck Shelter in the Firth of Clyde, January 2019 (Photo Michael Leek). Alternatively, Mass Swimmer Lock-Out (MSLO) operations can be carried out with the submarine at shallow depths where SF personnel swim out of the hangar to targets at short distances (or inflate dinghies, once on the surface). With limited space in the submarine and small hatches, the DDS hangar is a much better option to comfortably accommodate inflatable dinghies with outboard motors. Although less covert than using the SDVs, this allows a larger number of SF personnel to be delivered by dinghy. If the SDV is not embarked, the DDS can be used with the submarine on the surface or just awash. When the DDS hangar is pumped dry, ballast tanks on the submarine must be filled to compensate for the significant additional buoyancy, this process must be reversed when it is flooded again. Too shallow, and the boat could break the surface compromising the mission, too deep and the divers are at risk. When the SDV returns, support divers secure it to its cradle, winch it into the DDS, shut the hangar door before the water is pumped out.Ĭontrolling the submarine during this process is demanding for the crew as precise depth needs to be maintained while the boat remains in a stationary ‘hover’. After conducting their mission the SDV pilot may locate the mother submarine by active sonar pings. The SDV is winched out onto the cradle and the SF personnel get on board, prior to it being released. The large hangar door is opened and the rails used to guide the SDV onto the launch cradle mounted on the casing are extended. ![]() The compartment is sealed and then flooded up to equalise with outside pressure. To perform a mission, the special forces personnel and the support divers enter the hangar and dress in diving gear. (The US Navy version also has a hyperbaric decompression chamber forward of the transfer trunk but the UK version does not appear to have this facility.) Astute-Class-Submarine-Dry-Deck-Shelter-DDS-CHALFONT When the DDS has fitted, this chamber is mated to the ‘hangar’ which can accommodate either a Swimmer Delivery Vehicle (SDV) or up to 20 divers and their equipment. The Astute class reputedly have a lock-in/lock-out transfer trunk permanently installed inside the sail that allows diver access to and from the submarine while submerged. HMS Astute first deployed with the DDS on an 8-month patrol in 2014 and HMS Artful currently carries the DDS which she first received in late 2016. Given the small number of SSNs possessed by the RN, only one boat is likely to be fitted at a time. Securing points on the casing, hull penetrations, piping for high-pressure air and electrical supplies are in place ready to receive the DDS. The aft section of the sail on the Astute class boats have removable panels. The DDS is not a permanent fixture and is designed to be attached or removed from a submarine within a matter of days. In UK service it is formally named the Special Forces Payload Bay (SFPB) and was procured under ‘project CHALFONT’, although submariners nickname it “the caravan of death”. The DDS fitted to the Astute class boats is a cylindrical chamber approximately 13m long by 3m diameter. Using unclassified public domain sources, here we examine the history, design and operation of the DDS in RN service. The Astute class submarines were designed from the outset to be fitted with a Dry Deck Shelter (DDS) which significantly enhances their ability to covertly deliver special forces. ![]()
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