India's Fourth Arihant-Class SSBN, S4*, Expected to Be Commissioned as INS Arisudan: A Step Forward in Sea-Based Nuclear Deterrence

India is set to bolster its sea-based nuclear deterrent with the potential commissioning of its fourth Arihant-class nuclear-powered ballistic missile submarine, the S4*, which may be named INS Arisudan.

Defense Minister Rajnath Singh oversaw the submarine's launch on October 16, 2025, marking a significant achievement in India's indigenous strategic submarine development. Should the name Arisudan, meaning "destroyer of enemies" in Sanskrit, be officially approved, it will join the ranks of its predecessors INS Arihant, INS Arighaat, and INS Aridhaman.

The process of naming the submarine begins with the Indian Navy’s ship-naming committee and requires subsequent approval from the Ministry of Defence and the President of India. The expected commissioning of INS Arisudan in 2027 will considerably enhance India's nuclear triad amid changing regional security landscapes.

The third submarine, INS Aridhaman, is on the verge of induction and is anticipated to enter service in early 2026 following rigorous sea trials. This submarine, launched in November 2021 at the Ship Building Centre in Visakhapatnam, features a more advanced compact light water reactor, enhancing its stealth, endurance, and operational capabilities.

In comparison to INS Arihant, the newer submarines boast a larger size by about 1,000 tonnes and are outfitted with eight vertical launch tubes, allowing them to deploy longer-range submarine-launched ballistic missiles (SLBMs).

Initially armed with the K-15 Sagarika missile, which has a range of approximately 750 km, INS Arihant-class submarines have now been adapted to carry the K-4 SLBM, offering a reported range of around 3,500 km. Trials conducted by DRDO alongside the Strategic Forces Command have markedly improved India's second-strike capability.

As a key component of India's nuclear triad, SSBNs play a crucial role in maintaining the country's no-first-use nuclear policy by ensuring credible deterrence through continuous patrols at sea.

In addition to the Arihant-class, India is advancing the Project P-77 initiative to build indigenous nuclear-powered attack submarines (SSNs). This project, sanctioned in October 2024 with a budget of ₹40,000 crore, intends to construct two SSNs initially at Visakhapatnam with significant indigenous input, aiming for the first delivery in the mid-2030s.

While this new class is under development, India remains dependent on leased nuclear attack submarines, such as the Akula-class INS Chakra III, which Russia is expected to deliver in 2028.

The potential addition of INS Arisudan to the fleet later this decade highlights India's ongoing commitment to developing a robust and credible sea-based nuclear deterrent. This progress is pivotal to reinforcing India's strategic autonomy and security presence in the Indo-Pacific region.