The Author was the Flag Officer Commanding-in-Chief, Southern Naval Command when he retired on November 30, 2021. He is a Navigation and Direction specialist. He was also the Director General Naval Operations and the Chief of Personnel, Indian Navy.

The commissioning of the second SSBN of the Arihant-class, INS Arighaat at Visakhapatnam on August 29, 2024, by India’s Defence Minister, Rajnath Singh, marks another significant milestone in the development of India’s second-strike capability and the strengthening of our nuclear deterrence. The construction of Arighaat, reportedly commenced in 2009, and it was launched in November 2017. An upgraded variant of the Arihant-class submarine, it is the second nuclear-powered ballistic missile submarine made by India at the Ship Building Centre in Visakhapatnam.

As per open-source information, the submarine is powered by an 83 MW pressurised water reactor with a single shaft driving a seven-blade propeller, enabling it to achieve a maximum speed of 15 knots on surface and 24 knots when submerged. The submarine has four launch tubes in its hump, like Arihant, believed to carry up to 12 K-15 Sagarika missiles (each with a reported range of 750 km), or four K-4 missiles (with a likely range of over 3,500 km). The submarine is also armed with six torpedo tubes, which similar to other submarines, can carry a mix of torpedoes, missiles and mines.

Indian Navy’s First Nuclear Submarine INS Arihant

As per the Ministry of Defence (MoD), the technological advancements undertaken indigenously on Arighaat make it significantlymore advanced than its predecessor Arihant and this process will advance further after the commissioning of subsequent SSBNs. A comparative table with SSBNs of other countries reveals that India’s SSBNs are the smallest and most lightly armed, which is not surprising, considering that its expertise in building and arming such submarines is slowly reaching maturity.

While announcing the successful completion of the first deterrence patrol by India’s first SSBN, INS Arihant, on November 5, 2018, Prime Minister Narendra Modi had stated that, “... a credible nuclear deterrence is the need of the hour. The success of INS Arihant gives a fitting response to those who indulge in nuclear blackmail.” Speaking at the commissioning ceremony of Arighaat, India’s Defence Minister stated that it would further strengthen India’s three-tier retaliatory nuclear deterrent capability.

India’s ‘No First Use’ (NFU) nuclear weapons strike posture implies that India would not be the first to use nuclear weapons in war, and that its weapons would be only used to retaliate against a nuclear strike by an adversary. The NFU posture, adopted by stronger powers, depends on the credibility and survivability of its second-strike capability. The second-strike capability is, in turn, strengthened immensely by the presence of an underwater nuclear weapons strike capability, which is the most survivable of the nuclear weapon triad (land, air and seabased) because of its relative immunity from detection and targeting by an adversary. The undersea deterrent is also more plausible as on board a SSBN, SLBMs are already mated with nuclear weapons and only require an authorisation to be launched. In turn, a credible second-strike capability also plays a big role in deterring a first strike (and hence a nuclear conflict). It also strengthens the nonproliferation regime and promotes strategic stability while allowing scope for operations by conventional forces.

The second-strike capability’s credibility depends on the continuous availability of fully-armed SSBNs on deterrence patrol, requiring a minimum of three SSBNs for effective deployment

The credibility of a second-strike capability, however, is based on the round-the-clock availability of a fully-armed SSBN on deterrence patrol. There are two broad models for posturing SSBN-based strategic deterrence - an open ocean patrol model also called the ‘continuous at-sea’ model and the ‘bastion’ model. The ‘continuous at-sea’ model is ideal for maintaining credible strategic deterrence. This requires at least one submarine armed with nuclear weapons always deployed underwater. For this to be possible, a bare minimum force of three SSBNs is essential, to cater for one submarine on long-term maintenance and a second available on station to replace the submarine on completion of its deterrence patrol, or to replace it in case the submarine on deterrence patrol develops a technical snag. This model of deterrence, followed by the UK, France and China envisions a force-level at least three to four SSBNs, with one being on patrol at any time.

Superpower navies have much larger number of SSBNs on deterrence patrol to cater for the possible damage or destruction to a SSBN by enemy action, in case they are detected. The US Navy had 41 SSBNs in the 1960s, which were reduced to 14 SSBNs in 1994 because of the greater number of SLBMs with Multiple Independently-targetable Re-entry Vehicle warheads (MIRV) carried by each submarine. This is going to be further down-sized to 12 as the existing Ohio-class SSBNs are progressively replaced with the Columbia-class SSBNs. The Russian Navy has 16 SSBNs, of which eight are the new Borei-class and eight older boats.

The other option is the ‘bastion’ model employed by the USSR during the latter half of the Cold War and by both Russia and China today. This envisions SSBNs operating in home waters, protected by a layered defence, from which they can launch their SLBMs when required. This model was adopted by the Soviet Union because of the superior anti-submarine detection capabilities with the West, which could endanger their SSBNs (which were noisier than US submarines) in open waters. Hence, while bastions may be easier to identify, targeting SSBNs within them is very difficult because of the extensive defensive layers around them.

For India to maintain ‘continuous-atsea’ presence with two SSBNs is not going to be easy. It would, thus, be evident that India will require a force-level of at least three-four SSBNs, which is reportedly on the anvil. India’s SSBN programme is also reported to be moving towards larger SSBNs, the increased size being required to carry longer-range and greater number of SLBMs, which are essential to ensure second-strike capability against China. The DRDO has already successfully tested MIRV warheads on the Agni-V under Mission Divyastra, whose success was hailed by Prime Minister Modi on March 11, 2024. SLBMs of ranges up to 6,000 km, essential to reach the Chinese heartland from the Indian Ocean, are also reported to be under development. The recent induction of the sealed-canister-launched, solid-fuelled, road-mobile Agni-V ICBM (of range over 5,000 km), which allows India to cover the entire Chinese mainland, is indicative of the progress towards a longer range SLBM.

All said, India’s SSBN programme is its most shining example of Atmanirbharta, as most technologies and equipment associated with these weapon systems, such as nuclear propulsion, underwater sensors and acoustic stealth, are not shared by any country. The programme’s success is a fusion of the expertise and experience of the DRDO, Indian Navy and the Department of Atomic Energy and has significant contribution from both private and public sector units in India. A major reason for the success of the programme is the sustained funding and series construction of SSBNs, which ensures that lessons learnt from earlier designs are incorporated in subsequent boats. It also ensures that the human resources associated with the design, construction and operation of these submarines is retained, to the overall benefit of the programme – a lesson worth emulating for India’s conventional submarine and aircraft carrier building programmes.