India’s fourth Arihant-class nuclear-powered ballistic missile submarine, designated S4* and expected to be named INS Arisudan, advances the nation’s sea-based nuclear deterrence amid evolving regional security challenges. Launched by Defence Minister Rajnath Singh on October 16, 2025, at the Ship Building Centre in Visakhapatnam, the approximately 7,000-tonne vessel features eight vertical launch system cells, enabling it to carry up to 24 K-15 missiles (750 km range) or eight K-4 missiles (3,500 km range) for extended patrols in the Indo-Pacific. Currently undergoing sea trials that began in late 2025, INS Arisudan boasts over 80% indigenous content and is slated for commissioning around 2027, completing the Arihant-class fleet alongside INS Arihant, INS Arighaat, and INS Aridhaman, thereby bolstering India’s credible second-strike capability within its nuclear triad.