The propellers of the submersible, known as the Priz AS-28 mini-sub, became snagged on a fishing net or cable on Thursday, stranding it on the seabed off the Kamchatka peninsula, one of Russia's most easterly and heavily militarised points. The authorities said the submarine, itself a rescue vessel, was taking part in a military exercise.
Russian ships had to abandon attempts to cut it free from the net wrapped around the propeller. A new tactic - dragging the submarine along with the net into shallower water - brought quicker results.
Rescuers sought to drag the boat closer to shallower waters, but anchors and a large surveillance system was hindering the plan more than 40 hours after it snagged in deep waters.
"We moved it 100 metres towards the coast but the speed is not sufficient," said Admiral Viktor Fyodorov, the commander of the Pacific fleet. The crew are in a "satisfactory condition" and are trying to conserve oxygen by keeping movement to a minimum, said Navy officials.
Comparisons with the 2000 Kursk incident in which 118 sailors died were inevitable. The Russian Orthodox Church said its priests would lead services across the country praying for the men's survival.
After several confusing statements, the Navy said it expected the men's oxygen to run out some time this afternoon, explaining that their only hope lay with rescue teams since they were too deep to be able to swim to the surface.
Moscow ordered a fleet of 10 ships into the area. Two of the armada were yesterday dragging the seabed with anchors in the hope of snagging the fishing net or the submarine.
The Pacific Fleet insisted it had formulated a rescue plan that it was preparing to enact while America, Britain and Japan rushed to get rescue equipment to the scene. Both Washington and London were sending an unmanned "Scorpio" rescue mini-sub. Moscow's acceptance of foreign aid contrasted sharply with its stance during the Kursk disaster, after which it was criticised for being too slow and proud to admit the need for outside help.
A Russian Navy spokesman, Captain Igor Dygalo, said the sailors on the mini-sub were in satisfactory condition and had been told to conserve their energy and the craft's electricity. Voice contact was not possible, he added, but rescuers were able to communicate through other unspecified technical channels.
"The operation will continue non-stop until a result is reached," he promised on Russian television. "The AS-28 has enough air for one day. We have a day and we will continue our intense efforts to save the AS-28 and the people in it."
Captain Alexander Kosolapov, another naval spokesman, played down the incident's seriousness. "The situation is unusual. But it's not worth dramatising."
Russian media reported that the stricken vessel had passed a safety inspection last March and was declared seaworthy. Its predicament is bound to refocus attention on the state of the cash-starved Russian navy, which has been in serious decline since the collapse of the Soviet Union in 1991.
The Kursk submarine disaster was the worst but not the only catastrophe of recent years. It sank in the Barents Sea in Russia's far north after on-board explosions - 23 sailors survived the explosions, only to die lingering deaths as rescuers struggled to reach them. The explosions were eventually declared to have been caused by a faulty torpedo, although some Russians still believe a foreign submarine collided with it.
Last year, the navy faced criticism after it was forced to temporarily withdraw from service its flagship nuclear-powered missile cruiser Peter the Great because of fears that it "could explode at any moment".Reuse content