Limited options for rescuers

The Oscar class is among the largest submarines in the world

By Craig Francis
CNN.com writer

Rescuers are attempting to save the lives of more than 100 sailors trapped on board a sunken Russian navy submarine.

Rescue efforts began as senior Russian navy officers admitted the situation for the submariners was "serious."

Oxygen is being pumped into the Kursk via a bell attached to the submarine deck from a ship on the surface of the Barents Sea, off northwest Russia.

Even so, the crew of the Oscar-class cruise missile nuclear submarine have been told to sleep in order to conserve oxygen.

Paul Beaver, a spokesman for Jane's military information group, told CNN.com that although the partially flooded, Russian-built vessel had switched off some compartments of its nuclear-powered generating system, it could resume oxygen production if necessary.

As on the 11 other Oscar II class submarines, the generators on the Kursk serve as the vessel's gills, powering equipment that extracts oxygen from the water and allowing it to stay below the surface for more than three months.

Beaver says the most likely rescue mission would use a technique known as the "salvage blow".

"This involves using all available high-pressure air in the submarine itself, or connecting a high-pressure hose from the surface and blowing out the water in the flooded compartment, allowing a damage-control team in to seal the bulkheads or hatches," said Beaver.

With the debilitating weight of water expelled, the Kursk -- one of the world's largest submarines -- could then head to the surface under its own power.

Another plan, although one likely to be considered only after other options have been exhausted, would be to abandon the six-year-old vessel -- among the newest in the fleet -- on the ocean floor.

If the crew did need to be evacuated or provided with oxygen in an emergency, such a rescue mission would probably involve the use of smaller rescue submarines, known as DSRBs.

These rescue vehicles would provide an umbilical cord air supply to the incapacitated Kursk, while sealing an exit for the evacuation of the crew.

If matters worsened to the point where an immediate evacuation was necessary, the crew would be in serious trouble.

"At 150 metres below the surface, they are too deep to attempt an emergency ascent. Even with protective fibre suits to insulate them from the freezing cold water, it would be impossible to reach the surface alive from that depth," said Beaver.

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