India’s fourth Arihant-class SSBN, INS Arisudan nuclear-powered ballistic missile submarine, launched in October 2024, is undergoing advanced sea trials and is expected to complete them by the end of 2026, paving the way for commissioning around 2027.

This milestone will complete the first production series of India’s indigenous nuclear-powered ballistic missile submarine fleet, strengthening its sea-based deterrent posture.

The submarine, designated S4* during construction, was launched at the Ship Building Centre in Visakhapatnam in the presence of Defence Minister Rajnath Singh. After harbour integration and system validation trials, it departed Visakhapatnam in late December 2025 to begin sea trials, which are scheduled to continue through 2026 before commissioning preparations are finalised.

INS Arisudan is the second “stretched” Arihant-class variant, incorporating a larger hull section for missile storage and launch systems. It displaces approximately 7,000 tonnes, compared to the 6,000 tonnes of the lead boat INS Arihant.

The extended configuration increases missile capacity while maintaining reduced acoustic signatures and survivability features for long-duration patrols. Indigenous content is estimated at 75–80 percent, reflecting India’s progress in nuclear submarine construction under the Advanced Technology Vessel program.

A major upgrade introduced with INS Aridhaman and INS Arisudan is the expansion of the vertical launch system. Earlier submarines, Arihant and Arighaat, carried four VLS tubes optimised for K-15 Sagarika SLBMs.

The stretched variants feature eight VLS tubes, enabling carriage of up to eight K-4 SLBMs with a range of 3,500 kilometres, or alternatively 24 K-15 missiles with a shorter range of 750 kilometres. This significantly extends India’s deterrence reach across the Indo-Pacific.

The commissioning of INS Arisudan will complete the first generation of India’s SSBN fleet, joining Arihant, Arighaat, and Aridhaman.

Together, these submarines underpin India’s nuclear triad, which also includes land-based Agni missiles and air-delivered nuclear capability via Mirage-2000, Sukhoi-30MKI, and Rafale aircraft. Submarine-based nuclear forces are considered the most survivable leg of the triad, ensuring credible second-strike capability under India’s no-first-use doctrine.


Sea trials of INS Arisudan are expected to last roughly one year, with commissioning likely in early 2027. This will ease operational pressures by enabling a rotation cycle between patrol, repair, and training, while maintaining redundancy.

With four SSBNs, India will be better positioned to sustain a Continuous At-Sea Deterrent, though analysts argue that only the larger S5 class, projected at 13,500 tons, will provide undeniable robustness.

Strategically, INS Arisudan’s induction comes amid China’s expanding submarine fleet, which includes at least 12 nuclear-powered vessels and is projected to reach 80 attack submarines by 2035, half of them nuclear-powered.

Pakistan, meanwhile, maintains a first-use nuclear doctrine, increasing the importance of survivable deterrent assets for India. The construction of INS Varsha, a secure base south of Visakhapatnam with underground submarine pens, will further enhance survivability and concealment of India’s SSBN fleet.

The commissioning of INS Arisudan will mark the culmination of decades of effort since India’s nuclear tests in 1998 and the subsequent adaptation of SSN designs into SSBNs.

It represents both a technological and strategic milestone, strengthening India’s deterrence posture while laying the groundwork for the next-generation S5 class and nuclear-powered attack submarines.

Agencies