In a major setback to the Indian Navy, a Russian-made conventional submarine caught fire and sank at dawn with 18 sailors at the Mumbai dockyard Wednesday after two near simultaneous explosions.
But till late Wednesday night, the navy did not say if the three officers and 15 sailors were dead although Defence Minister A.K. Antony admitted in the morning to their deaths on board INS Sindhurakshak.
The deep sea attack vessel, recently refurbished in Russia, suffered an unexplained minor explosion just after Tuesday midnight. Immediately later came a deafening blast heard almost in the whole of south Mumbai.
In no time, the 2,300-tonne submarine, a Kilo class powered by a combination of diesel generators and electric batteries, was on fire, the flames leaping high.
TV footage of the incident showed a huge ball of fire lighting up the night sky in Mumbai's Colaba area where the heavily secured naval dockyard is located.
The fire lasted for nearly three hours before it was brought under control. The vessel eventually sank around dawn, with the 18 officers and sailors.
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Naval officials said the rapid spread of the fire and the intensity of the explosions left the trapped men with no chance of escaping.
"We cannot rule out sabotage," navy chief Admiral D.K. Joshi told the media after Antony visited the disaster site.
"But indications at this point do not support the (sabotage) theory," he said. "At this point of time we are unable to put a finger on what exactly could have gone wrong."
Naval sources said the blasts took place in the front portion of the 16-year-old submarine housing torpedoes.
A board of inquiry will submit its findings within four weeks.
It was the worst disaster to hit the Indian Navy, which has increasingly sought to dominate the expansive Indian Ocean region with blue water operational capability.
The incident came two days after India acquired its first indigenous aircraft carrier, INS Vikrant. The past week also saw the nuclear reactor that propels Arihant, the country's first ballistic missile submarine, going critical.
Admiral Joshi appeared to indicate that all the 18 may have perished: "We hope for the best and prepare for the worst."
By afternoon, navy divers entered the sunk vessel, only partly visible at the surface, after forcing open the jammed hatch.
The Mumbai Fire Brigade averted a greater tragedy by saving a second submarine at the dock.
Deputy Chief Fire Officer P.S. Rahandale told IANS that he saw another submarine berthed five-six metres away from the burning INS Sindhurakshak, which was not on active duty at that time.
"We built a wall of water-jets between Sindhurakshak and the other vessel, thereby giving it a safe window to sail to safety," he said.
Admiral Joshi said any number of factors could have led to the "major catastrophe"
He said the submarine had a large stock of ammunition, fuel and oxygen water. "Any combination of any of these malfunctioning could have resulted (in the explosion)."
He said the submarine had inbuilt safety measures but "obviously they have not functioned".
The submarine had returned after a major upgrade programme in Russia 3-4 months ago and was capable of carrying a potent weapons package including the anti-ship 'Club' missiles.
The incident has come at a time when the navy is faced with a depleting submarine fleet.
Retired Commodore Uday Bhaskar said since the rate of induction of new platforms has not kept up with the kind of wear and tear that a submarine suffers, the navy's submarine fleet was depleting and the operation load increasing.
"The fact that the Sindhurakshak (incident) has happened, it is going to have its own adverse impact," he said.
Vice Admiral (retd) A.K. Singh said he suspected that hydrogen gas generated during charging of the batteries of the submarine could have led to the disaster.
INS Sindhurakshak returned home last year after a major refit at Russia's Zvezdochka shipyard.
In 2010, a fire broke out on board Sindhurakshak leaving a sailor dead and two others injured. That mishap was caused by an explosion in its battery compartment.
But Joshi ruled out any link between Wednesday's incident and the earlier accident.
India bought the submarine from Russia as part of a deal in the early 1980s and the warship was commissioned in 1997. It was the ninth of the 10 'Sindhugosh' class diesel-electric vessels the Navy has in its 16-strong submarine fleet.