In February 2016 India announced that its first locally designed and built nuclear powered submarine, the 6,000 ton SSBN (ballistic missile carrying sub) INS Arihant (Destroyer of Enemies), had completed its sea trials and was ready for service. This comes after twelve years of planning and construction. Arihant was supposed to enter service before the end of 2015 but, as has happened so often with this project, there were more unforeseen technical problems to fix.
In 2013, four years after being publicly revealed, Arihant turned on its nuclear power plant for the first time. At that point it was felt that Arihant would be ready for sea trials by 2014. But there were more delays. India launched Arihant in 2009. What was not revealed at the time was that the Arihant was launched without its nuclear reactor, which was not ready until 2010. The Arihant was launched when it was because work on the sub had been going on for more than a decade and it was becoming embarrassing to have nothing to show for all that effort. According to the original plan, the first of six Arihants were supposed to enter service in 2008. That has been delayed several times and after 2009, Arihant had to return to dry dock to have the power plant installed.
Arihant was built to carry nuclear armed K15 ballistic missiles designed and manufactured in India. Arihant has four vertical launch tubes, which can carry twelve (three per launch tune) smaller K15 missiles or four larger K-4 (based on the Agni 3) missiles. The K-4 has a longer range of 3,500 kilometers. The K-4 is still in development. Two more Arihants are under construction. The Arihant is based on the Russian Charlie II sub, which it resembles. The Charlie class had eight launch tubes, outside the pressure hull, for anti-ship missiles. Arihant has a crew of 90-100 and six 533mm (21 inch) torpedo tubes in addition to the four vertical missile launch tubes.
In early 2013 the Indian K15 SLBM (Sea Launched Ballistic Missile) underwent its final development test and were ready to be installed in the Arihant. This came after five years of testing and tweaking. In 2007, India announced that it had perfected the technology for launching ballistic missiles from a submerged submarine. That meant the silo design had been perfected as well. In 2008, India began a series of twelve test firings from a missile cell designed to fit into the Arihant. These test firings were not done from the Arihant but from the cell placed in the ground or underwater to simulate launch from the sub. Seven launches took place in 2008.
The seven ton K15 has a 700 kilometer range with a one ton warhead or 1,900 kilometers with a 189 kg warhead. The latter weight is sufficient to handle a nuclear warhead if India has been successful in developing warhead technology to the same point the U.S. and Russia were in the 1980s.
The first SLBM was the U.S. Polaris A1, which began development in the 1950s and entered service in 1961. Like the K15 it was a two stage solid fuel missile. The Polaris A1 weighed 13 tons, had a range of 2,200 kilometers, and a one ton warhead.
Nevertheless the success of Arihant led to an SSN (nuclear attack submarine) program, which is now underway. In 2015 India announced ambitious plans to build six SSNs but admits development and building will probably take at least fifteen years. One locally made nuclear sub doesn't change the balance of naval power much for India, which is already dominant in the region but it does show that India can build nuclear subs and six SSNs will make a difference.