India sees Russia as a strategic counterweight to China but New Delhi has been upset by repeated delays to major weapon orders from Moscow, including the Admiral Gorshkov heavy aircraft carrier.
"We shall definitely supply this vessel to the customer by the end of this year," said navy commander Admiral Vladimir Vysotsky. A fully trained Indian navy crew were ready to receive the submarine, he said which some Russian media reported in 2010 had already been handed over to India.
The Nerpa, an attack submarine codenamed as "Akula" -- or "Shark" -- by NATO, is usually armed with torpedoes and cruise missiles. It can go down to depths of 600 metres (2000 ft) for about 100 days. It can carry 73 people.
According to Russian media, Nerpa's construction process started in 1991 -- the year the Soviet Union collapsed -- but funding was frozen in the chaotic 1990s and the submarine was only launched and started sea trials in 2008.
Twenty people died on the Nerpa due to the inhalation of the toxic gas used as a fire suppressant when its fire extinguishing system switched on unexpectedly at sea trials in November 2008.
This was the deadliest accident to hit Russia's navy since August 2000, when the Kursk nuclear submarine sank beneath the Barents Sea, killing all 118 sailors on board.