"We hope for the best and are prepared for the worst," he told reporters at the Western Naval Command headquarters.
He, however, said three other sailors, who were on the "upper casing" of the submarine when the tragedy occurred, survived, sustaining "only minor injuries". "They have been discharged (from the hospital)," he added.
"Miracles do happen... There may be some air pocket or some may have got access to breathing sack," he said when asked if there could be survivors among the 18 including three officers.
"A board of inquiry has been ordered which will bring out all the details," he said. The inquiry is expected to be completed in four weeks.
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"We do not have answers to what caused the fire," he said, adding "There are several ingredients (on a naval vessel) that contribute to or cause fire, including explosives, fuel, oxygen bottles.
"We hope to determine what caused this catastrophe," Joshi, who accompanied Defence Minister A K Antony to the naval dockyard, said.