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.