India’s next-generation S-5 ballistic missile submarine (SSBN) program could see its initial production run capped at four submarines instead of the six units previously discussed, as the Indian Navy reportedly examines the possibility of transitioning to a larger and more capable follow-on deterrent platform in the late 2030s.
According to defence sources, steel-cutting for the lead S-5 submarine commenced at the Shipbuilding Centre (SBC) in Visakhapatnam in late 2025, marking the formal start of construction for India’s most advanced sea-based nuclear deterrent asset. The government has also reportedly authorized concurrent construction of the first two submarines to accelerate production and maintain industrial continuity.
While earlier plans often referenced a six-boat S-5 fleet, current approvals appear to support an initial batch of four submarines, with the option to expand the class later based on strategic requirements and future force-structure decisions. The S-5 is expected to displace around 13,500 tons submerged, making it substantially larger than the Arihant-class and placing it among the world’s larger strategic submarine designs.
The move toward a four-boat fleet is believed to stem from evolving naval assessments following the introduction of larger Arihant variants such as S4 and S4*. These enhanced submarines were intended to bridge the capability gap before the arrival of the S-5 class, potentially allowing four high-endurance S-5 boats to sustain continuous deterrent patrols while older submarines assume training and secondary operational duties.
Sources indicate that planners are already studying future options beyond the S-5. One possibility is an enlarged “S-5 Plus” variant displacing nearly 17,000 tons, offering increased missile capacity, improved stealth, greater endurance, and higher reactor output. Another option under consideration is a completely new S-6 class incorporating next-generation reactor technologies, larger missile compartments, advanced acoustic suppression measures, and future long-range SLBM capabilities.
Although long-term plans remain under evaluation, the immediate priority is the timely completion of the first S-5 submarine, which is expected to enter service around 2033–34. Armed with advanced K-series submarine-launched ballistic missiles, including future long-range variants, the S-5 class is expected to become the cornerstone of India’s sea-based nuclear deterrent and significantly enhance the credibility of the nation’s second-strike capability.
