India’s fourth Arihant-class nuclear-powered ballistic missile submarine, INS Arisudan, is expected to complete its sea trials by the end of 2026, signalling rapid consolidation of the Indian Navy’s strategic deterrent capability as it operationalises successive vessels from its indigenously-built nuclear submarine fleet.
The submarine, designated SSBN-84 and built at the Ship Building Centre in Visakhapatnam under the Advanced Technology Vessel (ATV) project, will carry cruise missiles from the K-series family and is equipped with a Compact Light Water Reactor (CLWR) for propulsion. Its addition to the fleet represents a major milestone in India’s deterrent posture and the Ministry of Defence’s Make in India initiative in advanced defence systems.
The Arihant-class programme, India’s indigenous response to establishing a credible sea-based nuclear deterrent, began with INS Arihant (SSBN-80), which was inducted in 2016 after extensive trials. The follow-on vessels, INS Arighaat (SSBN-81) and INS Aridhaman (SSBN-82), have progressively incorporated design refinements and enhanced combat systems. INS Aridhaman was commissioned in April 2026 with improved stealth characteristics and expanded payload capacity-eight vertical launch system tubes compared to four on its predecessors-allowing deployment of a larger submarine-launched ballistic missile contingent.
INS Arisudan, consistent with the fourth-unit build philosophy, will inherit these operational enhancements while further extending India’s underwater strategic strike reach across the Indian Ocean Region. The vessel’s reactor-an upgraded variant of the CLWR fitted to INS Arihant-offers significantly lower acoustic signature and enhanced endurance, making detection by adversary anti-submarine assets substantially more difficult. The submarine will achieve submerged speeds of 24 knots.
Operationalisation of these four boats fulfils India’s declared policy of maintaining a survivable, second-strike nuclear capability at sea. With INS Aridhaman now commissioned and Arisudan entering the advanced trial phase, India’s SSBN force structure is taking definitive shape. The programme, managed jointly by the Navy and the Defence Research and Development Organisation (DRDO), has consistently met production milestones despite the technical complexity inherent in building nuclear submarines indigenously without foreign propulsion technology transfer-a constraint imposed by international non-proliferation regimes.
The fourth boat’s imminent trial completion underscores India’s submarine industrial capacity maturation and validates the indigenous design architecture developed over two decades. Once commissioned, INS Arisudan will join the operational fleet under Navy Chief Admiral Krishna Swaminathan and contribute directly to the nation’s continuous at-sea deterrent posture requirement.
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