Despite hours of searching the dark, muddy water inside a submarine crippled by twin explosions, Indian navy divers have yet to find the 18 sailors feared dead there, possibly because the heat of the blasts melted some hatches shut, the navy said Thursday.

 

There has been no word from the sailors — or even a knock on the submarine’s hull — since the explosions shot huge fireballs into the sky over a Mumbai navy base Wednesday morning.

 

“The trapped personnel have not been sighted nor recovered,” the navy said in a statement. It said round-the-clock diving efforts were being hampered by poor visibility inside the submarine.

 

“The heat of the explosion has melted parts of the internal hull, deforming the submarine hatches and preventing access to compartments,” the navy said.

 

“Eighteen brave sailors are feared to have lost their lives,” Prime Minister Manmohan Singh said in brief comments Thursday during a speech to mark the anniversary of India’s 1947 independence from Britain. “We pay homage to these brave hearts we have lost.”

 

The explosions in the submarine’s torpedo compartment sent nearby sailors jumping into the sea in panic and left the diesel-powered vessel partially submerged at a dock, with a portion visible above the waterline.

 

The navy statement said heavy duty pumps were being used to pump out water that flooded into the submarine after the explosions.

 

A navy official, speaking on condition of anonymity because he was not authorized to speak to the media, said there had been no contact with the sailors since the explosions, which lit up the sky above the base.

 

S.C.S. Bangara, a retired navy vice-admiral, said there appeared to be little chance that any of the sailors could have survived.

 

“There would have been signs of life through tapping of the hull by the sailors, which is a known procedure for the rescue of sunken submarines,” he said.

 

Because the submarine was docked, navy watchmen were on the submarine rather than the normal crew, Admiral D.K. Joshi, the navy chief, told reporters Wednesday in Mumbai. At least some weaponry exploded in the near-simultaneous blasts, he added.

 

A video of the explosions filmed by bystanders showed an enormous ball of red and yellow fire rising hundreds of feet into the air.

 

Navy spokesman Narendra Vispute said the cause of the explosions was being investigated.

 

The 16-year-old Russian-made submarine, INS Sindhurakshak, was hit by an explosion in 2010 that killed one sailor and injured two others. The navy said that accident was caused by a faulty battery valve that leaked hydrogen, causing an explosion in the vessel’s battery compartment.

 

The sub recently returned from Russia after a 2 1/2 year refit, overhaul and upgrade, said Rahul Bedi, an analyst for the independent Jane’s Information Group. Joshi, the navy chief, said it returned to India in April, and had been certified for use by the Indian navy.

 

Russian ship repair company Zvyozdochka said the blasts were unrelated to its repair work.