INS Aridhaman is a nuclear-powered ballistic missile submarine (SSBN), designated S4, and the third vessel of the Indian Navy's Arihant-class. It is a concept and an institution, representing the sea-based leg of India's nuclear deterrent.
The vessel's origin lies in the indigenous Advanced Technology Vessel (ATV) Project, which aims to build India's nuclear submarine fleet. INS Aridhaman was laid down in 2018, launched on November 23, 2021, and commissioned on April 3, 2026, by Defence Minister Rajnath Singh. The primary problem it solves is ensuring a credible and survivable second-strike capability under India's "No First Use" nuclear doctrine.
As an SSBN, it works by operating stealthily underwater for extended periods, powered by an indigenously designed 83 MW Compact Light Water Reactor (CLWR). The submarine has a displacement of approximately 7,000 tonnes and can achieve a submerged speed of up to 24 knots. A key mechanism is its missile capacity: it is equipped with eight Vertical Launch System (VLS) tubes, which is double the four tubes on its predecessors, INS Arihant and INS Arighaat. This allows it to carry up to 24 K-15 Sagarika missiles (750 km range) or eight K-4 missiles (3,500 km range).
INS Aridhaman is directly connected to India's Nuclear Triad, which is the capability to launch nuclear weapons from land, air, and sea. It operates under the Strategic Forces Command (SFC). It is an upgraded variant of the Arihant-class. The most recent change is its commissioning on April 3, 2026, which solidified India's position among a select group of nations with an operational nuclear triad. The vessel's design represents an upgrade, being larger and featuring an improved CLWR with a lower acoustic signature, while the core concept of a nuclear-powered ballistic missile submarine remains the same.