In February the first Indian designed and built nuclear powered submarine, the 5,000 ton SSBN (ballistic missile carrying sub) INS Arihant completed sea trials and entered service. This comes after twelve years of planning and construction. Arihant was supposed to enter service before the end of 2015 but there were more unforeseen technical problems to fix. Nevertheless Arihant was commissioned as a navy ship in August 2016 even though it had not carried out its sea trials. These commenced in late 2016 and were successful.

Arihant was launched in 2009 but completing the sub kept running into problems. 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. There are also plans to build five more SSBNs based on the experience with Arihant.

Meanwhile in March 2016 India successfully tested its new K-4 SLBM (Sea Launched Ballistic Missile) under realistic conditions. This consisted of a submerged silo (like the one used in a submarine) that successfully released the missile at a realistic depth. The missile reached the surface, ignited its rocket motor and completed its ballistic flight as it was designed to do. Several more successful tests like this are required before K-4 can enter service. K-4 is based on the Agni-III land based ballistic missile, which has been in service since 2010. Both the Agni-III and K-4 have a range of 3,500 kilometers. K-4 is a 20 ton, two stage, solid fuel missile that carries a one ton warhead.

Arihant was built to carry nuclear armed K-4 or K-15 ballistic missiles designed and manufactured in India. Arihant has four vertical launch tubes, which can carry twelve (three per launch tube) of the smaller K-15 missiles or four larger K-4s. 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 533 mm (21 inch) torpedo tubes in addition to the four vertical missile launch tubes. Two more Arihants are under construction.

In early 2013 the K-15 missile underwent its final development test and was 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 K-15 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 K-15 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.