AT LEAST 20 Russian sailors and civilians died and 21 others were injured when a nuclear submarine's fire extinguishers accidentally activated during tests in the Sea of Japan.
Saturday's incident was Russia's worst naval incident since torpedo explosions sank another nuclear-powered submarine, the Kursk, in the Barents Sea in 2000, killing all 118 seamen aboard, and it has raised questions about the state of the country's military hardware.
It has occurred as the Kremlin seeks to reassert its military authority: Moscow's warplanes have resumed regular long-distance missions and, following August's victorious war with Georgia, a naval squadron is now heading to Venezuela for joint exercises this month in a show of force near US waters.
"During sea trials of a nuclear-powered submarine of the Pacific Fleet, the firefighting system went off unsanctioned, killing over 20 people, including servicemen and workers," said Russian navy spokesman Igor Dygalo.
"The submarine's nuclear reactor was operating normally and radiation levels were normal," he said, adding that the accident affected two sections of the submarine closest to the bow, while the reactor is housed in the rear of the vessel.
Investigators were immediately dispatched to Russia's Pacific coast, where the submarine safely returned to port near the city of Vladivostok. The navy said 208 people - or almost three times the vessel's normal crew - were on board the submarine.
Seventeen of the dead were civilian technicians and three were sailors.
It was not clear why portable breathing apparatus usually issued to Russian submarine crews did not save them from poisoning by a gas that was reportedly released by on-board fire extinguishers.
"Results of a preliminary investigation show that death occurred as a result of freon gas entering the lungs," the prosecutor general's office said in a statement.
Although the crew were issued with breathing devices, "it's probable the submariners didn't notice the inflow of gas and when they felt it, it was already too late," one Russian news agency quoted an unidentified official at navy headquarters as saying.
Local media said the high-speed attack submarine was called the Nerpa, and was due for delivery to India's navy. Construction reportedly began in 1991 and became bogged down because of lack of funding after the collapse of the Soviet Union. The vessel only submerged for the first time last week.
Following the Kurskdisaster, the Kremlin was criticised for its sluggish and secretive response and for the parlous condition of much of Russia's navy.
In August 2003 nine sailors died aboard a Russian submarine that sank in the Barents Sea while being towed to port for decommissioning. And in 2005 a mini-submarine of the Pacific Fleet got caught underwater in a fishing net, and was saved only through the help of a British rescue team.
"This . . . signals that, though Russia is increasingly assertive and aggressive on the geopolitical stage, it still faces very real challenges in terms of the revitalisation of its naval power," said Stratfor, a US-based security consultancy.
