On September 4th South Korea launched the first of two rescue and salvage ships. These will replace retired American ships (built in the 1970s) that South Korea has been using for over a decade. These new ATS (the letter code for Salvage and Rescue Ships) type vessels are equipped to send down divers to sunk ships and bring back essential equipment (like code books or secret electronics) and bodies of sailors.
ATS ships, like the new 3,500 ton South Korean vessels, can also clean up oil spills and tow ships displacing up to 15,000 tons (which takes care of the largest ships in the South Korean navy). There is also sonar and remotely controlled camera equipment to get a close look at sunk ships, or the hulls of those still afloat and badly danged. An ATS ship can also handle submarine rescue, including recovering sailors trapped inside a sunk ship. But that gear is only good for shallow waters (down to 90 meters/272 feet).
For deep water rescue, especially from submarines, South Korea can call on its own, British made, DSRV system. But South Korea can also call on portable submarine rescue equipment, like the American SRDRS (Submarine Rescue Diving and Recompression System). This is a modular system that weighs under 200 tons and can be flown anywhere on the planet within 72 hours (faster depending on the distance and availability of heavy transport aircraft). The SRDRS was designed to be operated from most merchant ships, as an ATS type ship won't always be available soon enough.
SRDRS consists of two main components. There is the rescue module, which is a remotely controlled submersible that descends to the stricken sub, attaches itself to the rescue hatch, and has room for 16 sailors. Once on the surface, the sub links to a decompression chamber, where the sailors have to stay for a while to acclimate them to surface pressures (and prevent the bends). In addition to the rescue vehicle and decompression module there is support equipment. There are also smaller underwater vehicles and pressure suits for divers. These are flown in first, to explore the stricken sub in detail, clear any debris from the subs rescue hatch, and basically gather information so the actual rescue can be carefully planned.
Five years ago Britain, Norway, and France completed the construction of the NATO Submarine Rescue Vehicle (SRV). This is very similar to the SRDRS and DSRV. NATO SRV was a $95 million project that resulted in a deep water rescue device that can be airlifted to anywhere in the world on short notice, fit on the deck of at least 140 identified ships, and mate with the escape hatches on most of the worlds' submarines, and carry up to 15 men at a time to the surface. This system is shipped in eleven waterproof cargo containers that can be flown by military or civilian cargo aircraft. Including flight time, set up time on the ship, and movement time to the site of the distressed submarine, the NATO SRV should be able to get there and have the SRV in the water within 72 hours. The SRV itself is ten meters (31 feet) long and weighs 27 tons, has a crew of three and can go as deep as 1,000 meters (which is the maximum depth for most submarines).
The U.S. and NATO systems are very similar but not identical. The basic idea behind this modular design is to enable the rescue system to reach the stricken sub as soon as possible. Once the air runs out down there rescue is no longer possible. All the navies of the world are invited to modify, if necessary, their rescue hatches (usually just the main hatch on the top of the sub) to accept the U.S. or NATO rescue vehicles. If they do that, the NATO or U.S. rescue systems (depending on whose is closest) will be sent to attempt a rescue. The U.S. system is based in California, the NATO one in northern Europe. South Korea could call on either one in case of a submarine emergency.