INS Arihant is the lead ship of the Arihant-class, India’s first indigenously built nuclear-powered ballistic missile submarines (SSBNs). Commissioned in August 2016, Arihant made India only the sixth country in the world, and the only one outside the five permanent members of the UN Security Council, to design, build, and operate a ballistic missile submarine, completing the sea leg of India’s nuclear triad.[1]
The Arihant programme, formally the Advanced Technology Vessel (ATV) project, was one of independent India’s most closely guarded and technically ambitious defence programmes, combining indigenous naval reactor development with submarine hull design and integration of a new class of submarine-launched ballistic missiles. Development drew on decades of work by India’s Bhabha Atomic Research Centre and Defence Research and Development Organisation (DRDO), alongside naval architecture support, to produce a genuinely indigenous nuclear submarine rather than a licence-built or leased design.
INS Arihant is powered by an 83 MW pressurised water reactor fuelled with enriched uranium, giving the submarine effectively unlimited submerged endurance limited only by crew provisions rather than fuel, a defining advantage of nuclear over conventional diesel-electric propulsion for a strategic deterrent platform that must remain concealed for extended patrols.[2]
Arihant carries four vertical launch tubes, each capable of holding up to three K-15 submarine-launched ballistic missiles (12 in total) with a range of around 750 km, or, in an alternative loadout, a smaller number of the longer-range K-4 missile. The K-4, a solid-fuelled, two-stage ballistic missile developed by DRDO, has a range of approximately 3,500 km and can carry a nuclear payload of around two tonnes, giving India a far more credible second-strike range than the shorter-legged K-15 alone could provide.[3]
The second Arihant-class boat, INS Arighaat, was commissioned on 29 August 2024 and features an expanded eight-tube missile configuration, doubling capacity to eight K-4 missiles or 24 K-15 missiles, a significant leap in strike capacity over the four-tube Arihant. In December 2025, India conducted a successful user trial of the K-4 missile from an operational SSBN, INS Arighaat, in the Bay of Bengal, validating the missile in an operationally representative test rather than a developmental trial. A third boat, INS Aridhaman, was reported by the Indian Navy Chief in December 2025 to be nearing commissioning.[4]
As a survivable, mobile, and difficult-to-detect platform, the Arihant-class underpins the credibility of India’s “No First Use” nuclear doctrine, which depends on the certainty of being able to deliver a retaliatory nuclear strike even after absorbing a first strike against land-based forces. Analysts have noted that the K-4’s longer range, once operationally proven aboard INS Arighaat, makes the shorter-ranged K-15 largely obsolete for genuine strategic deterrence, since it requires the submarine to patrol dangerously close to adversary shores to bring targets within range.[5]
The Arihant-class represents the most technically demanding and strategically consequential platform in India’s indigenous defence-industrial base, combining nuclear engineering, submarine construction, and long-range missile development into a single integrated deterrent system. Its continued expansion, with Arighaat’s larger missile load and Aridhaman’s impending commissioning, reflects a deliberate build-out of a multi-boat SSBN fleet intended to maintain continuous at-sea deterrent patrols.
| Type | Nuclear-Powered Ballistic Missile Submarine (SSBN) |
| Manufacturer | Indigenous (Advanced Technology Vessel project, India) |
| Propulsion | 83 MW pressurised water reactor (enriched uranium) |
| Missile Tubes | 4 (Arihant); 8 (Arighaat and later boats) |
| Armament | K-15 SLBM (~750 km range); K-4 SLBM (~3,500 km range) |
| Commissioned | August 2016 (INS Arihant); August 2024 (INS Arighaat) |
| Boats in Class | INS Arihant, INS Arighaat, INS Aridhaman (pending commissioning) |