India has become the sixth country to operate a nuclear submarine with the commissioning of the leased Russian Akula-II class K-152 Nerpa on Jan. 23, contributing to the fledgling third leg of India’s nuclear triad.

The 8,140-ton Akula II, capable of remaining underwater for months, was rechristened INS Chakra. It has set sail from a Russian base near Vladivostok and is expected to reach India within a month. The submarine will be based at the southern port of Visakhapatnam. Its 10-year lease is worth $920 million.

Russia, the U.S., the U.K., France and China are other operators of underwater nuclear vessels.

Akula-II class submarines are equipped with 28 nuclear cruise missiles with a striking range of 3,000 km (1,875 mi.). The Indian version is reportedly expected to be armed with 300-km Club nuclear missiles. A senior naval official says the submarine is not armed with long-range missiles due to international nonproliferation treaties such as the Missile Technology Control Regime. The introduction of this highly sophisticated platform will give Indian naval personnel training on how to operate nuclear reactors and other systems, he adds.

The new 10-year lease flows from the January 2004 agreement, with India funding a major part of the Nerpa’s construction at the Komsomolsk-on-Amur shipyard after Russia stopped it midway due to a financial crunch. The Nerpa had been scheduled for delivery in 2008, but an accident during sea trials forced Russian authorities to put it on hold.

Unlike diesel-electric submarines that need to surface every few days to get oxygen to recharge their batteries, and have limited endurance due to fuel requirements, nuclear-powered submarines are stealthy and can operate underwater at long ranges.

“These submarines operate at very large depths of over 500 meters, significantly enhancing their capability to operate undetected. The greater the depth, the more difficult it is to pick up acoustic and electromagnetic signals of submarines,” the official says.

According to a defense expert, India has 16 old submarines, four of which are of German origin and the rest from the former Soviet Union. India is currently completing development of its own Arihant-class nuclear-powered ballistic missile submarines.

The submarine leg of the triad is proving the most difficult of the three to achieve and far more complex than the land and air legs. India has been endeavoring to build this leg of the triad since the mid-1980s.

“The Akula-II platforms [with a submerged displacement of 12,390 tons] are well equipped to perform this role,” the official says.

While the Agni and Prithvi missiles represent the land leg of India’s triad, the air leg comprises Jaguar, MiG and Sukhoi aircraft.