On Aug. 15 an explosion ripped through the front section of an Indian navy submarine, the INS Sindhurakshak, sinking the vessel at its dock in Mumbai. Eighteen sailors went down with it.
If a tragic event occurred with a U.S. Navy vessel, could the personnel onboard be saved?
For most modern navies, the answer is yes. There are two ways to rescue people in a disabled submarine: a tethered chamber that's lowered to the disabled sub and then raised with the sailors, and a deep submergence rescue vehicle, or DSRV.
The U.S. Navy uses the tethered method. Their version, called the Submarine Rescue Diving Recompression System, or SRDRS, has three components -- one for each stage of a rescue operation.
In the first stage, a diver in a specialized suit, called an atmospheric dive system, that can reach depths of 2,000 feet swims to the submarine to confirm that the hatch is accessible and whether there are survivors.
"He'll make sure the sub is intact, and maybe tap on the hull," Lieutenant Commander Andrew Platten, executive officer of the Undersea Rescue Command, told DNews.
Once it's clear that there are survivors and the hatch works, the next step is to call in a remotely operated vehicle, called a pressurized rescue module, or PRM. Typically crewed by two people, the vehicle – which can also dive to 2,000 feet, can hold an additional 16 people. It links to the submarine hatch using a "skirt" -- essentially a tube that covers the hatch and pushes out the water with pressurized air. The outside water pressure seals the tube onto the hatch the same way air pressure holds a suction cup to a wall.
The sailors exit the submarine through the skirt, board the PRM and go to the surface where the vehicle docks with a larger pressure chamber. The chamber slowly reduces the air pressure inside until it matches that of the surface in order to avoid giving the sailors decompression sickness.
A pressurized rescue module, or PRM can hold two crewmen, up to an additional 16 people, and can reach depths of 2,000 feet.US Navy / Mass Communication Specialist 2nd Class Alexia M. Riveracorrea
If for some reason a rescue team can't get to a submarine or the situation in the submarine is too dangerous, Navy submariners trapped inside can swim out using a specially designed suit called the Submarine Escape Immersion Equipment. It's designed to provide air at one atmosphere for several minutes and float the user to the surface, where it automatically deploys an inflatable raft. It can work down to depths of about 600 feet.
The suit replaced the old method, called a Steinke hood, which was a kind of collapsible gas mask. "It was basically a bag over your head," said Tom Stowell, managing director at James Fisher Defence, a U.K.-based company that supplies submarine rescue systems to industry and various navies. A former submariner himself, Stowell noted that the problem with the hoods was that they didn't protect against hypothermia. Seawater can be cold and anyone floating in the ocean without some protection won't last long. The new suits, on the other hand, keep the user warm.
James Fisher Defence makes a craft called the Deep Search and Rescue that's used by several navies. Stowell said one advantage it has over other methods is that it can reach subs under ice. Although it's designed to reach depths of 1,600 feet, it can reach 2,300 in a pinch.
Thankfully neither of these systems has been needed -- yet -- to actually recover U.S. sailors at depth. The closest thing to a rescue in recent years was the use of an unmanned remotely operated vehicle to save a Russian submarine, the AS-28, at a depth of about 600 feet. The AS-28 -- itself a deep-sea rescue vehicle -- had gotten tangled in cables used to anchor hydrophones. The ROV, a James Fisher vehicle, cut the cables, allowing the AS-28 to surface.
Stowell said that even though navies use different systems, any time a submarine goes down, the effort to rescue it is an international one -- at least in peacetime. The U.S. Navy offered help to the Russians when the Kursk went down in 2000, killing 118 sailors.
"It's really kind of a brotherhood," he said, noting that submariners in different countries tend to have a lot in common.
Sadly, none of these systems would have helped much in the Sindhurakshak disaster. According to recent reports the temperatures inside the sub were so high that there is little chance anyone could have survived. Platten said he and other submariners were saddened by the news of the Sindhurakshak, as crews from both navies had gotten to know each other during the exercises last year.
"We shook hands with those guys," he said.