The Evolution of US Combat Diving. Part 4, the DDS.

The Dry Deck Shelter Evolution.

This is Part 4 of 7 taken from my Submarine Medical Officer Thesis “A Review of the Combat Diving Evolution of US Naval Special Warfare with a Focus on the Necessity of Disruptive Technologies and Innovative Scientists.” Stay tuned for part 5…

The Dry Deck Shelter

The Dry Deck Shelter (DDS) was another invention that greatly expanded the combat divers’ capabilities. As described in Captain Robert Gormly’s memoirs, before the DDS, the deployment of a UDT/SEAL team from a submarine was a lengthy and uncomfortable process. The lock-out trunk – located in the forward torpedo room – could only fit one dive pair and the trunk operator at a time, and the lock-out process for a dive pair lasted nearly ten minutes. If a mission required an entire platoon, deployment from the submarine could take hours – not an ideal situation for the submarine or the UDTs.1

During the entire lock-out process, the submarine maintained a slow heading at a shallow depth making it vulnerable to discovery and attack. Also, the lengthy process prolonged the environmental exposure for the UDTs who were already preparing for an extended underwater infiltration. Although the SDVs could technically be deployed from other platforms – helicopters and ships – submarines were still the ideal platform because of the ability to deploy undetected, underwater, and relatively near an objective.2

The USS Grayback. The predecessor to the DDS program was the USS Grayback (SSG-574, see Fig. 11), a diesel-electric submarine with two large forward hangar bays designed to carry the Regulus Missile System – an early hybrid of an intercontinental ballistic missile (ICBM) and a cruise missile. As originally designed, the submarine would surface, open its hangar doors, fire its missiles, close its hangar doors, and submerge again. When the Regulus missile system was abandoned in favor of the Polaris ICBMs in 1964, the Grayback was decommissioned – its special design no longer needed. Astute UDT leadership recognized the unique value of the dual hangar submarine, and the Grayback was refitted and re-commissioned in 1968 for use with the evolving UDT SDV platoons. The large wet and dry sections of the empty missile bays were perfect for storing, berthing, and launching the UDT/SEALs, their equipment, and the SDVs. Also, the wet hangar sections were modified to flood, pressurize, and open underwater allowing an entire SDV platoon to deploy quickly and secretly while the submarine remained submerged.3,4,5

Figure 11: USS Grayback before being retrofitted for SOF use. Notice the dual missile hangars.6

The DDS Concept and Creation. The USS Grayback continued hosting UDT/SEAL training and operations until early 1983 when its aging lifespan prompted the Navy to seek a replacement system. Since no other available submarines had this unique hangar system, an adaptation of the Grayback concept was created – the Dry Deck Shelter (DDS).7,8 The DDS is a long cylindrical pod composed of three separate compartments that fastens just aft of the sail on the deck of the submarine. The most forward compartment is a hyperbaric chamber for the treatment and decompression of injured divers. The middle compartment, or “transfer trunk,” provides divers access to and from the other “spheres” of the DDS and a means of transit into and out of the submarine. The most rearward compartment is a large, elongated hollow tube that serves as a hangar for the staging and launching of SDVs, combat divers, and Combat Rubber Raiding Crafts (CRRCs). Each chamber is capable of pressurizing to at least 130 feet, and the majority of the DDS structure is enclosed in a protective cover that serves as an undersea fairing. The DDS can be used to deploy the SDVs and their crews or it can be used to deploy up to twenty divers simultaneously with a CRRC in a Mass Swimmer Lock-Out (MSLO) – a means of quickly deploying a relatively large specialized maritime force.9

Large nuclear powered submarines originally designed to launch ICBMs were modified to host the DDSs. The empty missile bays of these submarines provided ample room for an SDV platoon, its support personnel, and their equipment – similar to the Grayback concept. Unlike the Grayback which was reserved only for SOF training and missions, the first DDS modified submarines were not solely dedicated to SOF. They were often stripped of their shelters and employed as attack subs which made them unavailable to the SEALs for training or operations. Later, additional submarines were fitted with dual shelters (Fig. 12), and a few fast attack submarines were fitted with single shelters.10,11,12 This expanded the undersea SOF versatility and created an infrastructure of multiple deployable undersea platforms capable of hosting continual SDV operations.

Figure 12: An Ohio class submarine outfitted with dual Dry Deck Shelters.13

The Impact of the DDS. The DDS was the final technological piece that integrated the combat diver, the SDV, and the submarine. The SEALs and Divers have found a home in the empty missile bays of SSGN submarines and deploy for weeks or months at a time with the submarine crew. SOF, Divers, and Submariners were an odd match at first, but the more they worked together, the more symbiotic their relationship became.14 With the DDS, the SEALs deployed much more efficiently when compared to previous practices (Fig. 13&14). Also, the hyperbaric chamber was a lifesaver for injured divers. These three revolutionary technologies – the re-breather, the SDV, and the DDS – and the dedication to constant adaptation and evolution created “the most technically advanced, operationally capable combat swimmer force in the world.”15

Continued in Part 5…


  1. Gormly, Combat Swimmer, 5-21.
  2. Kelly, Brave Men, 167-169.
  3. Ibid., 152-153, 168-169
  4. Dockery, Complete History, 470-471
  5. Steve Southard, “Dry Deck Shelters – Deploying Special Operations Forces from Submarines,” NAVSEA’s Deckplate, 1 (Jan-Feb 1999), accessed February 1, 2015,
  6. “USS Grayback SSG-574, Shown as configured prior to 1968,” picture, accessed December 19, 2015,
  7. Kelly, Brave Men, 168-169
  8. Southard, “Dry Deck Shelters.”
  9. Southard, “Dry Deck Shelters.”
  10. Kelly, Brave Men, 169
  11. Southard, “Dry Deck Shelters”
  12. Lonsdale, United States Navy Diver, 235-239
  13. Ohio class submarine with Dual DDS Shelters, picture, accessed December 19, 2015, uploads/2012/02/ohio_ssn_729.jpg.
  14. Kelly, Never Fight Fair, 200.
  15. Joiner, Naval Forces: A Look Back, 2-16, 17.
  16. “SEAL Delivery Vehicle Team Two members prepare to launch one of the team’s SDVs from the back of the submarine USS Philadelphia,” picture, accessed December 19, 2015, SEAL_Delivery_Vehicle.
  17. MK VIII SDV and Open Hangar Door, picture, accessed December 19, 2015, http://www.americanspecialops .com/images/seals/sdv-2.jpg

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