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INS Arihant : The Ballistic Missile Submarine is giving India’s Nuclear Triad a lethal edge

The K series of missiles is emerging as the principal submarine-launched ballistic missile (SLBM) series to give India its much sought after nuclear triad. Wikipedia defines SLMB as a ballistic missile capable of being launched from submarines. Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs) each of which carries a nuclear warhead and allows a single launched missile to strike several targets. Submarine-launched ballistic missiles operate in a different way from submarine-launched cruise missiles.

In 2009, the INS Arihant – the lead vessel of a class of at least three ballistic missile submarines (SSBN) was launched. After lengthy trials, the INS Arihant was commissioned and on 5 November 2018, the vessel completed its first deterrence patrol. This marks an important step towards developing the final leg of India’s intended nuclear deterrence triad. With a displacement of 6000 tons, a length of 111 metres and powered by an 83 MW pressurized water reactor, the INS Arihant has a maximum speed of some 24 knots and has been tested to a depth of some 350 metres. The submarine, though there was significant input from Russia, is the first nuclear-powered vessel to be built in India and represents a remarkable technical achievement for both India’s defence research and development agencies as well as its shipbuilding industry. Its armament consists of 533mm torpedoes and, as befits its task as a ballistic missile submarine, between four and twelve submarine-launched ballistic missiles fitted with nuclear warheads with the number of missiles being dependent on the type carried.

India efforts have been concentrated on developing two SLBMs – the 750km range K-15 and the 3500km range K-4 to be deployed aboard the Arihant class of ballistic missile submarines. The K-15 underwent at least twelve development trials from a submerged pontoon aimed at simulating a submarine. However, on 25th November 2015, an unarmed K-15 was purportedly fired from the INS Arihant. It should be stated that this has not yet been confirmed by Indian officials and no photographs have emerged of such a launch from the Arihant. The limited range of the K-15 makes it very much an interim system, although twelve of them could be carried by the Arihant.



The K-4 was first tested on 24th March 2014 from a submerged pontoon. Another pontoon launch followed on 7th March 2016. Thereafter it was reportedly tested from the INS Arihant itself on 31st March 2016. It would be surprising if such a major development were not highlighted in some way but in any event, development of the K-4 is clearly well in progress. Four such missiles are to arm the Arihant class and the K-4 bears a striking resemblance to the land-based Agni-III dimensionally and in respect of its performance. The K-4 has some way to go before it can be inducted into service, however, once it does, the INS Arihant and its sisters will have a much more viable weapon at their disposal, though the limited number of missiles carried will be a distinct drawback. It is anticipated that from the INS Arighat onwards, the number of K-4 missiles will increase to eight per vessel, making the SSBNs far more effective and flexible.

Two successor missiles – the K-5 and K-6 – are reportedly planned for a follow-on class of SSBNs, displacing more than twice that of the Arihant class. The 13,500 ton SSBNs of the so-called S-5 class are to carry twelve of the 5000km range K-5 – development of which started in 2015, with no tests done to date – or a similar number of the 6000km range K-6 which is to have multiple independently targetable re-entry vehicles (MIRVs). It could be safe to suggest that the longer-ranged K-5 could replace the K-4 on the Arihant class to enhance the effectiveness and flexibility of the SSBNs still further.

Just as the Agni series has emerged as the backbone of India’s land-based nuclear deterrent, the K-series is emerging as the principal SLBM series to give India its much sought after nuclear triad. This is no mean achievement and correctly portrayed as a major technological step forward. On the other hand, the Arihant class is a relatively modest vessel by the high standards set by the five larger nuclear powers which operate much more potent vessels. It has to be stated, however, that India is a relative newcomer to the sphere of nuclear-powered submarines and its move to build and deploy an SSBN as its first vessel using such propulsion, is extremely ambitious and despite the inevitable challenges, the vessel is a remarkable achievement. In fact, it might have been expected for India to develop an SSN – like the Akula class submarine currently leased as the INS Chakra. By opting for an SSBN, it is clear India allocated priority to the Arihant project with plans for six SSNs being left for the future.

However, while the INS Arihant does mark an important step forward for India’s nuclear triad, care should be taken not to assume that this leg of the triad is either complete or totally credible. Until the K-4 is operational, the INS Arihant has next to no deterrent capability vs China. In addition, additional SSBNs are needed to allow for continuous patrols. These two necessary steps will take time to come to fruition.

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