India has formally commissioned a nuclear-powered submarine into its navy, rejoining the elite club of nations with such a weapon.
The $1bn (£630m) Russian-built vessel is being leased by the Indian navy for the next 10 years. It was handed over to India in eastern Russia in January.
India previously operated a Soviet nuclear submarine until 1991.
It now rejoins China, Russia, the US, the UK and France as an operator of nuclear submarines.
India is also developing its own nuclear-powered submarine which is expected to be ready by the end of this year.
'Big boost for navy'
The 8,140-tonne Akula II-class submarine, built by the Russians as the K-152 Nerpa, has been renamed by India as the INS Chakra II.
The submarine was formally commissioned into the navy by the country's Defence Minister, AK Antony, at a ceremony in Vishakhapatnam, on India's east coast off the Bay of Bengal.
"This will be a big boost for the Indian navy," Mr Antony told reporters after the ceremony.
"The INS Chakra will ensure security and sovereignty of the country," he said.
It has a crew of 80 under the command of Captain P Ashokan.
The submarine set sail from the Russian port of Vladivostok 40 days ago, the BBC's Sanjoy Majumder reports from Vishakhapatnam.
In keeping with international non-proliferation treaties, the submarine will not be equipped with nuclear weapons. It will only carry cruise missiles, our correspondent adds.
India had previously leased a nuclear submarine from the Russians in the late 1980s which was used to train its naval personnel.
The INS Chakra will, however, be operational and is expected to give the Indian navy an added advantage, our correspondent says. It is capable of remaining submerged for about three months at a time.
It was due to be handed over to Delhi in 2009 but the transfer was delayed because of problems during testing.
In November 2008, at least 20 people died in an accident on the Nerpa when a fire extinguishing system was activated by mistake.
India is also building an indigenous nuclear submarine, the Arihant, which is expected to join the navy some time later this year.
Russia is also expected to help India train the Arihant's crew.
India and Russia are long-time allies and Russia supplies 70% of India's military hardware.