The Indian Navy's fourth nuclear-powered ballistic missile submarine, codenamed S4*, marks a significant milestone in India's strategic underwater capabilities, with recent reports confirming its indigenous content exceeds 80 per cent.

Launched on 16 October 2024 at the secretive Ship Building Centre in Visakhapatnam, the S4* is currently undergoing fitting-out before sea trials commence, positioning it as the most advanced vessel in the Arihant-class lineage.

This submarine embodies a stretched design variant, often dubbed 'Arihant 1.5', featuring enlarged dimensions that accommodate a greater missile payload compared to predecessors like INS Arihant and INS Arighaat.

Equipped exclusively with the indigenous K-4 submarine-launched ballistic missile (SLBM), boasting a 3,500-kilometre range, the S4* employs vertical launch systems for enhanced salvo flexibility, far surpassing the shorter-range K-15 missiles of earlier boats.

Powered by an 80MW pressurised water reactor developed domestically, the vessel achieves submerged speeds exceeding 30 knots, with endurance limited only by crew provisions and maintenance needs.

The high indigenisation level—over 80 per cent—stems from contributions by key Indian entities, including the Defence Research and Development Organisation (DRDO) for missile systems, Bhabha Atomic Research Centre (BARC) for reactor technology, and shipyards like Mazagon Dock Shipbuilders Limited.

This figure surpasses the approximately 75 per cent indigenous content reported for prior Arihant-class units, reflecting matured domestic manufacturing prowess in hull fabrication, propulsion, and sensors.

Private sector involvement has accelerated timelines, overcoming past hurdles such as welding complexities and acoustic stealth refinement that delayed earlier submarines.

Within the broader Advanced Technology Vessel (ATV) program, initiated with initial Russian assistance but now predominantly home-grown, the S4* bolsters India's 'Credible Minimum Deterrence' and 'No First Use' nuclear doctrine.

It completes the first quartet of SSBNs: INS Arihant (commissioned 2016), INS Arighaat (August 2024), INS Aridhaman (nearing commissioning post-trials), and now S4*.

The S4*'s expanded hull potentially houses up to 24 K-4 missiles, rivalling regional adversaries' capacities and ensuring a survivable second-strike option amid Indo-Pacific tensions.

Geopolitically, it counters China's Type 094 Jin-class SSBNs in the Indian Ocean, safeguarding vital sea lines for energy imports while integrating with P-8I aircraft and Project-75(I) submarines.

Recent sea trials for the class, including S4*, underscore operational maturity, with dual-crew rotations enabling continuous deterrence patrols.

Future evolutions, such as S5-class boats with K-5 missiles (5,000 km range), will further extend reach, incorporating Agni-VI derivatives.

This indigenisation triumph not only reduces foreign dependency but elevates India's shipbuilding expertise, paving the way for sustained SSBN fleet expansion by early 2027.

IDN (With Agency Inputs)