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DSRV technology

Submarine force is the most vital component of any military and it is the ultimate deterrence against the enemy but if the navy loses its platform and human resources in the midst of a war then it can be a big disaster to overcome.

There are dozens of incidents since 19th Century where submarines and crews lost their lives in a critical manner and it ultimately led to innumerous pain and lingering agony, taking decades or more to recuperate with the situation.        

Indeed, losses in early submarine history inevitably led to the need for being able to rescue submarine crew members trapped in a distressed submarine (DISSUB) on the ocean floor.

From the earliest diving-bell rescue vessel, submarine rescue has grown into its own command. Today, various navies coordinate submarine rescue efforts among several other countries’ navies to provide global rapid-response submarine rescue capabilities to any nation whose crew members are trapped in a DISSUB.

The submarine rescue system had undergone an extensive refurbishment period. Dedicated and professional submariners combined with robust and redundant submarine systems ensure that submarines are inherently safe. In addition, the Submarine Rescue Diving and Recompression System (SRDRS) provide a last line of defence for the rescue of a submarine crew.

The Pressurized Rescue Module (PRM-1) Falcon, which is the submarine rescue vehicle component of the SRDRS, is capable of diving to depths up to 2,000 feet and mating with a disabled submarine trapped on the sea floor. The SRDRS is capable of being flown anywhere in the world to rescue either US or partner nation submariners in distress.

After World War Two, new methods and approaches were adopted to boost the survivability of submarine crew.

The traditional method of escape, where the crew of the distressed submarine (DISSUB) leaves the boat and reaches the surface without assistance, was replaced by aided ascent due to improvements in technology.

However, there were limitations in both methods of escape. The chances of suffering from decompression illness remained high and neither provided protection to the submariner against the elements once he reached the surface.

This was evident from the collision and sinking of HMS Truculent in 1950. All 72 crew members made it to the surface, but only 15 survived while the rest were lost at sea (according to the Royal Navy Submarine Museum).

The success of the McCann Bell was a leap of improvement but proved to have its limits as well. The system could only operate in less turbulent seas and shallower operating depths as it required divers to secure guiding lines to the DISSUB along which the rescue chamber descended.

Submarines in combat have been documented back to the Revolutionary War when the Turtle was designed to attach explosives to moored British ships. As submarines became increasingly abundant, the unfortunate loss of life in the early stages of submarine development made the necessity for submarine rescue capabilities increasingly apparent.

Following the losses of USS S-51 (SS 162) in 1925 and USS S-4 (SS 109) in 1927, Submariner and eventual Vice Admiral Charles Momsen began thinking of ways to rescue sailors who were trapped on sunken submarines and conceived the idea of a diving bell.

Under the guidance of eventual Vice Admiral Allan McCann, the diving bell was completed and christened as a submarine rescue chamber (SRC) in late 1930 and was produced as the McCann Rescue Chamber.

In 1939, USS Squalus (SS 192) sank due to mechanical failure, sitting at a depth of 243 feet. The SRC made its debut, with both Momsen and McCann observing rescue operations. After 13 hours and four dives, the lives of 33 of the 59 Sailors were saved, marking the first successful submarine rescue and paving the way for the future of submarine rescue.

At the same time, the US Navy also needed an area from which to base and launch rescue efforts. Thus the Submarine Rescue Unit (SRU) was born.

Located on the northern side of Naval Air Station North Island in San Diego (NASNI), SRU became home to the DSRV units Mystic and Avalon and the improved SRCs.

In 1989, the Navy changed SRU’s name to Deep Submergence Unit (DSU) until 2012, when it became today’s URC and was transferred from Submarine Development Squadron 5 and added as a tenant command of Commander, Submarine Squadron 11 (CSS-11), located across the channel at Naval Base Point Loma.

In 2013, Rear Admiral Phil Sawyer, Commander Submarine Force, US Pacific Fleet, assumed overall responsibility for submarine survivability, escape and rescue matters.

When USS Thresher (SSN 593) was lost with all hands in 1963, and the wreckage was found at depths up to 8,000 feet, which far exceeded the capability of the SRC’s 850-foot depth, the Navy knew it needed something with greater dive and rescue capabilities.

“The US Navy recognized our old idea of having submarine rescue ships with submarine rescue chambers did not work out very well for a modern navy,” said Commander Andy Kimsey, commanding officer of Undersea Rescue Command (URC).

This need for a deep-rescue capability initiated the US Navy’s Deep Submergence Rescue Vehicle (DSRV) design and procurement.

URC’s submarine response and rescue capabilities can be broken down into three categories: shallow-water rescue, deep-water rescue, and intervention.

The shallow-water system is composed of two SRCs and support equipment that make up the Submarine Rescue Chamber Flyaway System (SRCFS).

The SRCFS can be pack- aged up and loaded onto an Air Force C-5 or two C-17s for rapid worldwide mobility. The SRCs themselves are relatively unchanged from the original design by Allan Rockwell McCann in the 1930s.

The SRC is capable of diving to 850 feet and is operated by two internal attendants to retrieve six pas- sengers at a time from a disabled submarine.

For deep-water rescue, the primary asset is the Pressurized Rescue Module (PRM-1) Falcon, which is a remotely operated tethered vehicle that is lowered into the water from a vessel of opportunity.

Two attendants man the vehicle to facilitate rescue efforts and control and monitor life support functions.

Designed for submerged transit to a depth of 2,000 feet, the PRM has a capacity to rescue 16 personnel at a time. Integral to the design of the PRM is the transfer skirt attachment that assists the PRM in mating to the disabled submarine.

The PRM is part of the overall Submarine Rescue Diving and Recompression System (SRDRS) at URC. Another leg in SRDRS is the Assessment/Underwater Works System (AUWS), which includes the Atmospheric Diving System (ADS).

ADS is essentially a suit worn by a diver and is used as an intervention piece. The ADS interior remains at one atmosphere, allowing the pilot to operate at depths to 2,000 feet for extended periods and return directly to the surface without the attendant costs and risks associated with decompression.

The ADS provides a rapid response capability for DISSUB localization and assessment, hatch clearance, and emergency life support stores replenishment.


Submarine rescue is the primary mission of URC and, whether it is a US submarine or a foreign country’s submarine, URC is ready to respond. “We view submarine rescue as an apolitical mission,” said a senior US commander.

“Our job is to rescue human beings that are on the ocean floor and can’t get up. It is independent of politics, it is independent of international relations, and it is independent of whatever mission that submarine was doing.”

What makes URC so open to international engagements is the fact that they operate at the unclassified level, allowing anyone to gain access and insight to what URC is capable of accomplishing.

Furthermore, URC conducts regular exercises with various nations. Every three years, URC performs an exercise in Europe with the NATO Submarine Rescue System (NSRS) and other international systems.

In addition, URC operates every three years with Pacific-based nations in a submarine rescue exercise called Pacific Reach. And almost annually, URC conducts exercises with Chile as part of the Diesel-Electric Submarine Initiative (DESI) program.

The primary goal in the event of a distressed submarine is survival of the crew. If for some reason the crew cannot be rescued by an SRC, they have another option: the Submarine Es-cape Immersion Equipment (SEIE).

The SEIE is an escape suit, encompassing the entire body that inflates, carrying the crew member to the surface, and provides both protection from hypothermia and a separately inflatable single-person life raft.

The SEIE may be employed in an “abandoned ship” scenario from the surface or during an escape from underwater. The first device designed for individual escape from a distressed submarine was the Momsen Lung.

It was developed in the 1930s by later Vice Admiral Charles Momsen and used soda lime to remove carbon dioxide from exhaled air so that it could be re-breathed.

The Momsen Lung was used only once, aboard USS Tang (SS 306) during WWII, which had sunk in 180 feet of water.

An improvement on the Momsen Lung was the Steinke Hood, developed in 1961, which is an inflatable life vest with a hood that completely encompasses the head, trapping a bubble of breathable air.

As the escapee rises through the water, water pressure decreases, causing additional breathable air to move into the hood.

The biggest drawback of these two systems was the lack of thermal protection for the escapees once reaching the surface to await rescue.

Protection suit

To address this concern, a British company, Beaufort Air-Sea, developed the SEIE in 1997. The SEIE enables submarine crew members to escape a DISSUB from as deep as 600 feet, nearly doubling the depth from which the Steinke Hood could be used.

The air inside the suit propels the escapee upward through the water at about 10-12 feet per second. Using the SEIE, eight to ten people can escape to the surface from a DISSUB per hour.

Each crew member must don the suit and step into the escape trunk. The escape trunk is then flooded and pressurized to match the external water pressure, at which point the external hatch can be opened.

The buoyancy of the suit propels the crew members to the surface, and the suit then protects them from exposure to the elements. Converting submarines to use the SEIE required both crew training and reconfiguring the escape trunks.

Today the SEIE is standard equipment on all US submarines. The US Navy saw renewed interest in individual rescue systems in part because US submarines are operating in the shallower littoral areas more than they did during the Cold War.

This means that, if there is a DISSUB incident, there is increased likelihood that it could happen at depths from which an individual rescue system would be viable. In the event of such an emergency, the SEIE may just be what saves the lives of submariners.

As navies develop submarine capabilities, it’s necessary to build up a submarine rescue capability-be it individually or collectively-as a parallel development.

In June 2004, the UK, France and Norway placed a contract with Rolls-Royce Power Engineering to develop a new system-the North Atlantic Treaty Organisation (NATO) Submarine Rescue System (NSRS).

It was to replace the UK submarine rescue system. The UK Defence Procurement Agency, on behalf of the three participants, manages this tri-nation project.

Turkey, a participant during the project definition phase, remains an observer nation while it considers future financial involvement.

The NSRS Submarine Rescue Vehicle (SRV) entered service in end 2008. Unlike the unmanned and tethered Falcon, it is operated by two pilots in its command module, has a capacity for 14 rescuees, and can descend to a depth of 600 metres.

To boost its endurance, Rolls-Royce incorporated its ZEBRA battery technology in the SRV. When compared to the lead-acid battery, the ZEBRA battery has almost doubled the submersible’s energy density and endurance.

In 2008, the People’s Liberation Army (PLA) Navy acquired a new submarine rescue vehicle, LR7, from Perry Slingsby Systems.

The 25-feet-long submersible can operate at depths of more than 300 metres and has a capacity for 18 rescuees. In addition, the PLA Navy also launched a new Type 926 Submarine Rescue Ship constructed by the Guangzhou Shipbuilding Company.

Swift Rescue is an 85-metre-long vessel built using the American Bureau of Shipping specifications and equipped with Dynamic Positioning-2 capability.

It houses the rescue payload, certified by classification society Lloyd’s Register, on its main deck where the main bulk of the rescue mission will be executed.

Centred at the aft deck, the 30- tonne LARS is able to launch and recover the submersible up to Sea State 5 without the aid of swimmers.

DSAR6, operated by two pilots and with a capacity for 17 personnel, is normally stowed in the sheltered hangar mid-ship on the main deck where the TUP system is installed.

The submersible DSAR6 has an aft hatch to enable the pressurised transfer of personnel into the TUP system. A Deck Handling System is in place to move the submersible from its stowed position to under the LARS for deployment.

Swift Rescue also houses the ROV system which can be deployed to survey or inspect the DISSUB site and assist to clear debris around the rescue hatch before deploying DSAR6.

The comprehensiveness of the rescue approach is evident, especially in the medical facilities that have been incorporated on board the Swift Rescue.

Besides the TUP system, medical areas for various treatments (e.g. triage, sickbay and high dependency ward) have been identified.

The ship is also able to handle escape scenarios. The six-man Rigid Hull Inflatable Boat is equipped with a scoop to facilitate the recovery of personnel at sea.

Upon recovery, they can either be transferred to Swift Rescue via its side jetty, or directly onto its main deck depending on the sea conditions.


Adherence to international standards, where possible, has been practised for the systems design evolution.

For instance, all hatches and interfaces are standardised to STANAG 1297 rules. This allows interoperability with the systems and submarines of other nations that meet the same standards.

Sophisticated technology, equipment reliability and redundancy as well as system safety are critical for the success of rescue missions.

Swift Rescue is equipped with the Integrated Navigation & Tracking System, which monitors the ROV, DSAR6 and DISSUB underwater during operation.

To enhance security in submarine operations during peacetime, navies recognise that the submarine rescue capability is an important aspect to boost the psychological well-being of the submariners.

As efforts continue to break technology barriers to attain higher effectiveness and responsiveness in missions such as rescuing the DISSUB crew, there is much more that needs to be done to ensure rescue success. International cooperation and collaboration remain vital in complementing a nation’s capability.

Inspired by the Kursk tragedy, the International Submarine Escape and Rescue Liaison Office (ISMERLO) was established in September 2004 under the auspices of NATO and the Submarine Escape and Rescue Working Group (SMERWG).

This was a significant step towards global assistance in submarine search and rescue operations. With its web based coordination tools, ISMERLO is able to facilitate rapid call-out for international rescue systems in the event of a submarine accident.

The works of SMERWG and the importance of ISMERLO are gradually being recognised, especially in the international response and aid administered to the Russian AS-28 Priz submersible incident.

Through these lessons, nations are now practising their coordinated rescue efforts regularly. Multilateral search-and-rescue at sea exercises such as Sorbet Royal7 and Pacific Reach are held regularly with participation from NATO members and Asia-Pacific nations respectively.

Development of more robust coordination, especially in establishing standardisation, will continue to be a challenge.

Mutually accepted standardisation in terms of aspects such as submarine rescue seat design as well as communication script for the SRV and DISSUB is recognised to be crucial for submarine rescue.

This allows consistency and compatibility to be established upfront among the different submarines and submarine rescue systems in the world, thus saving time during an emergency rescue.

SMERWG, in particular, covers technical and procedural issues concerning all aspects of the subject with the aim of disseminating information and establishing mutually accepted standards for the design and operation of submarine escape and rescue systems.

Modern technology

The equipment used in deep-sea rescues is like something from a James Bond movie. From remote-controlled subs with robot arms to deep-sea diving suits, modern technology has greatly increased the odds of a successful rescue.

Remote-operated vehicles (ROVs) are a crucial part of deep-sea rescue. These underwater craft range in size from 2 feet long to the size of a small car.

They are typically tethered to another submarine or surface ship. The power and remote capabilities are supplied by this tether, which also provides a conduit for the video and audio relay cables.

ROVs are usually equipped with both video and still cameras. They also have remote-operated robotic arms with lifters, grabbers, pinchers and cutters.

Many times an ROV is sent down to access the situation so the crew can decide the best course of action for response. If the disabled submarine is simply trapped or has lost power, the ROV can often cut it free or tow it to the surface.

Hard-shelled suits that can withstand pressure as deep as 2,000 feet, known as Atmospheric Diving Suits (ADS), were put into action in 2001.

With a constant internal pressure of one atmosphere, the ADS allows divers to ascend to the surface at any rate of speed without requiring decompression.

With this technology, human divers are now able to access situations firsthand, provide emergency life support and prepare the sub for mating, the process of joining the vessel to another.

Submarine Rescue Chambers (SRCs) are metal pods that can be attached, or mated, to a disabled submarine.

These chambers remain pressurized and allow for the safe extraction of the crew. Once on board, the SRC detaches from the sub and ascends to the surface at a safe rate.

There is a similar unit called a Transportable Recompression Chamber System (TRCS) that’s used in the evacuation and recompression of deep-sea crew.

A transfer lock attaches and forms an airtight seal between the sub’s hatch and the TRC, allowing medical personnel to go back and forth in a pressurized environment. Like the SRC, the TRCS is pulled back to the surface by a cable and the crew is gradually recompressed.

Another new addition to the deep-sea rescue fleet is the Emergency Evacuation Hyperbaric Stretcher (EEHS), portable, collapsible one-man chamber that are used to move individual sailors to safety in a pressurized environment.

Sorbet Royal may sound like a French dessert, but it is actually the most intensive deep-sea rescue training exercise in the world.

The NATO-sponsored event is held every three years, alternating between locations in the Baltic and Mediterranean Seas.

Sorbet Royal 2005 floated its way into Taranto, Italy, for 11 days of multinational rescue exercises with participants from 24 nations, including, for the first time, divers and submariners from the Ukraine and Russia. The goal of each Sorbet Royal is to top the previous one in the intensity and scope of the exercises.

Italy, the Netherlands, Spain and Turkey supplied the subs to be used for the exercises-each one taking turns being sunk several hundred feet to the bottom of the ocean with crew members aboard. The complexity of the rescue scenarios was intensified at the 2005 Sorbet by staging rescues of multiple vessels instead of one at a time.

The different countries responded together, sharing techniques and learning the compatibility of the equipment they use. Submarines travel great distances from their home bases, and the ability of other countries to respond to a distress call is crucial to the successful rescue of the crew.

The submarine community is tight-knit and crosses international boundaries. The 2005 Sorbet was an important one.

There have only been 170 deep-sea accidents in the 120-year history of the submarine, but eight have been in the last 10 years. This includes the 2005 loss of the Russian nuclear submarine, Kursk. In that accident, the sub was disabled 350 feet down, with 118 crew members aboard. The British Navy responded to the alert but was unable to save anyone. The loss of the Kursk was a strong motivator for the Russians to participate in the 2005 exercise.