India’s sea-based nuclear deterrent is set for a major upgrade as the country prepares to commission its third indigenous Arihant-class nuclear-powered ballistic missile submarine (SSBN), INS Aridhaman (S4), by the summer of 2026. Currently in its final stages of sea trials, the vessel is expected to be inducted into the Strategic Forces Command (SFC) between April and May.
The commissioning marks a critical expansion of the Advanced Technology Vessel (ATV) project. Built at the Ship Building Centre in Visakhapatnam, the S4 represents an “Arihant-stretch” design, offering significant improvements in payload capacity and stealth over the earlier INS Arihant and INS Arighaat.
Also Read | Imran Khan and Bushra Bibi Sentenced to 17 Years in Jail
The S4 Upgrade: Larger, Quieter, Deadlier
Unlike its 6,000-tonne predecessors, INS Aridhaman displaces approximately 7,000 tonnes and is roughly 10 meters longer. This extra space is primarily dedicated to an expanded missile compartment.
-
Missile Loadout: It can carry either 24 K-15 Sagarika missiles (750 km range) or 8 K-4 SLBMs (3,500 km range).
-
Stealth: The submarine features an upgraded 83 MW pressurized water reactor and improved acoustic damping with anechoic tiles, making it significantly harder for adversary sonar to detect.
Continuous At-Sea Deterrence: The Strategic Shift
With three operational SSBNs, India will enter an elite group of nations capable of maintaining Continuous At-Sea Deterrence (CASD). This policy ensures that at least one nuclear-armed submarine is on deep-sea patrol 365 days a year, providing a “credible second-strike” capability. In the event of a land-based strike, these “invisible” platforms ensure that India can retaliate, upholding its no-first-use nuclear doctrine.
Also Read | Imran Khan and Bushra Bibi Sentenced to 17 Years in Jail
Regional Undersea Arms Race: China & Pakistan
The commissioning is timely as regional undersea dynamics shift.
-
Pakistan: Islamabad is set to induct its first Chinese-designed Hangor-class submarine in 2026. This $5 billion deal for eight Air-Independent Propulsion (AIP) equipped vessels aims to challenge India’s maritime dominance in the Arabian Sea.
-
China: The PLA Navy already maintains a larger fleet of six Jin-class SSBNs. India’s focus on the S4 and the subsequent S4* (INS Arisudan) is designed to close this gap while the next-generation S5-class submarines remain under development.
Reality Check
The Navy expects the S4 to be operational “by summer.” Still, sea trials for nuclear assets are notoriously rigorous and prone to last-minute technical delays. Therefore, while April–May is the target, formal induction often quietly slides by a few months if reactor parameters require fine-tuning. In fact, the S4 was originally anticipated for 2025, showing that “final stages” can be an elastic term in strategic procurement.
The Loopholes
The Indian Navy is leasing an Akula-class attack submarine (Chakra III) from Russia, but delivery has been pushed to 2028. In fact, recent reports suggest India may abandon plans for a second Russian lease to focus on the indigenous Project-77 (nuclear attack submarines). Therefore, the “gap” in India’s attack submarine fleet remains a vulnerability until these indigenous boats arrive in the mid-2030s. Still, the Project-75(I) deal with Germany for conventional AIP boats provides a much-needed bridge for littoral defense.
Also Read | Imran Khan and Bushra Bibi Sentenced to 17 Years in Jail
What This Means for You
If you are a follower of national security, understand that the S4 commissioning completes the “Triad” in a way that is virtually indestructible. First, realize that these vessels will be based at Project Varsha—a high-security underground pen near Visakhapatnam—keeping them safe from satellite surveillance. Then, monitor the upcoming flight tests of the K-5 missile (6,000 km range); the S4 is designed to eventually carry these longer-range “city-killers.”
Finally, understand that naval spending will increasingly pivot toward these “silent” platforms. You should expect the Indian Ocean to become a theater of “cat-and-mouse” games between Indian SSBNs and Chinese/Pakistani hunter-killer submarines. Before the year ends, watch for the official naming ceremony of the S4*, which will likely be the final boat of the Arihant class.
What’s Next
INS Aridhaman is expected to complete its deep-submergence trials by late March 2026. Then, a high-profile commissioning ceremony at Visakhapatnam is tentatively scheduled for April 2026. Finally, the government is expected to clear the final design phase for the massive S5-class SSBNs (13,500 tonnes) by the end of the fiscal year.
Also Read | Imran Khan and Bushra Bibi Sentenced to 17 Years in Jail
End…
