India’s strategic submarine programme has reached another important stage with the fourth Arihant-class nuclear-powered ballistic missile submarine, identified as INS Arisudan, progressing through advanced sea trials. The submarine is expected to complete its trials by the end of 2026, potentially clearing the way for its commissioning in 2027.
The submarine was launched in October 2024 at the Ship Building Centre in Visakhapatnam. It is the fourth and final vessel of the Arihant-class series and represents a further evolution of India’s indigenous nuclear-powered ballistic missile submarine capability. Recent reporting indicates that the vessel has already entered sea trials, an important phase involving testing of its propulsion, underwater performance, sensors and other critical systems before operational induction.
The progression of INS Arisudan comes as India continues to strengthen the sea-based component of its nuclear triad. Nuclear-powered ballistic missile submarines, or SSBNs, are central to maintaining a survivable second-strike capability because they can remain concealed underwater for extended periods and provide a strategic deterrent even if other nuclear forces come under attack.
India currently operates INS Arihant and INS Arighaat, while the third Arihant-class submarine, INS Aridhaman, was inducted in 2026. The addition of the fourth submarine would provide greater depth to India’s SSBN fleet and support more sustainable at-sea deterrence patrols. Analysts have noted that having multiple SSBNs is particularly important for maintaining continuous availability while allowing other submarines to undergo maintenance, training and replenishment.
INS Arisudan is based on the stretched configuration developed for the later Arihant-class submarines and is expected to incorporate improvements over the earlier boats. Open-source reporting has associated the submarine with the K-4 submarine-launched ballistic missile system, although operational details of India’s SSBN fleet remain closely guarded. The K-4 is designed to provide a longer-range submarine-launched strike option, strengthening the strategic reach of India’s underwater deterrent.
The submarine programme also highlights the growing role of India’s domestic shipbuilding and nuclear technology capabilities. The Arihant-class project has been developed under India’s Advanced Technology Vessel programme, involving extensive participation from Indian defence and nuclear establishments. The first submarine, INS Arihant, entered service in 2016, followed by INS Arighaat in 2024. The commissioning of INS Aridhaman in April 2026 further expanded India’s operational SSBN force.
The expected completion of INS Arisudan’s sea trials by the end of 2026 will therefore be closely watched as India moves toward the next stage of its strategic submarine programme. If the vessel completes testing successfully, its expected commissioning in 2027 would mark another significant milestone in India’s efforts to maintain a credible and survivable nuclear deterrent at sea.