On March 7 2016 India successfully tested its new K4 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 K4 can enter service. K4 is based on the Agni 3 land based ballistic missile, which has been in service since 2010. Both the Agni 3 and K4 have a range of 3,500 kilometers. K4 is a 20 ton, two stage, solid fuel missile that carries a one ton warhead.
A month before this K4 test the first locally designed and built Indian nuclear powered submarine, the 6,000 ton SSBN (ballistic missile carrying sub) INS Arihant (Destroyer of Enemies) completed its sea trials and was ready for service. This comes after twelve years of planning and construction. Arihant was built to carry nuclear armed K4 or K15 ballistic missiles designed and manufactured in India. Arihant has four vertical launch tubes, which can carry twelve (three per launch tune) of the smaller K15 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 533mm (21 inch) torpedo tubes in addition to the four vertical missile launch tubes. Two more Arihants are under construction.
In early 2013 the Indian K15 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.