India has reportedly launched sea trials for its fourth Arihant-class nuclear-powered ballistic missile submarine, designated S4. This 7,000-tonne vessel, expected to be commissioned in early 2027, can carry eight K-4 ballistic missiles with a 3,500 km range. The S4 boasts over 80% indigenous content, aligning with India's self-reliance goals in defense. Upon its induction, India will operate four SSBNs, enhancing its underwater strike capability.