" INS Aridhaman S4 " India Third Nuclear Submarine Ready For Sea Trials, Join Navy in 2025

Visakhapatnam, August 2025 – India is preparing to induct its most advanced nuclear-powered ballistic missile submarine yet, the INS Aridhaman (S4), which is currently undergoing sea trials and is expected to be commissioned later this year. The submarine, built at the Ship Building Centre in Visakhapatnam, represents a major leap in India’s Arihant-class SSBN program and will greatly enhance the nation’s nuclear triad.

Bigger, Quieter, More Lethal

Weighing around 7,000 tonnes, Aridhaman is significantly larger than India’s first two Arihant-class boats. It is powered by an 83 MW CLWR-B1 nuclear reactor, an upgraded design that allows longer patrol endurance and a quieter acoustic signature, making it harder for enemy navies to detect.

At nearly 130 meters long and capable of reaching 24 knots submerged, the submarine is designed for extended deterrence patrols in both the Arabian Sea and Bay of Bengal. Nuclear propulsion means it can stay at sea indefinitely, limited only by crew endurance and supplies.

Missile Firepower

Aridhaman carries eight vertical launch tubes, double the capacity of India’s lead boat INS Arihant. These tubes can be loaded with:

Eight K-4 SLBMs with a range of about 3,500 km
Or the future K-5 SLBMs, with an estimated range of 5,000–6,000 km
Alternatively, up to 24 shorter-range K-15 missiles

This greatly improves India’s second-strike capability, allowing Aridhaman to strike targets deep inside enemy territory while remaining hidden at sea.

Indigenous Effort

The submarine boasts about 70% indigenous content, showcasing India’s growing expertise in submarine construction, reactor design, sonar systems, and weapons integration. Systems like the USHUS sonar and Panchendriya combat suite highlight how far Indian shipbuilding has come since the first SSBN project began in the late 1990s.

Class Status and What’s Next

INS Arihant (S2) – commissioned in 2016, first deterrence patrol in 2018.
INS Arighaat (S3) – commissioned in August 2024.
INS Aridhaman (S4) – undergoing sea trials, expected in service by late 2025.
Fourth hull (S4)* – launched in October 2024, under construction with expanded missile capacity and further reactor improvements.

By the early 2030s, India aims to field a fleet of at least four operational SSBNs, ensuring that one submarine is always at sea on deterrence patrol.

Strategic Significance

Aridhaman comes at a critical time for India’s defense posture. With China expanding its nuclear submarine fleet and Pakistan moving ahead with Chinese-built Hangor-class conventional submarines, the ability to keep nuclear weapons survivable at sea is vital. Unlike land-based or air-based nuclear forces, a submarine operating silently underwater provides the most credible assured second strike in case of a nuclear exchange.

The arrival of Aridhaman will allow India to shift from a single-hull nuclear deterrent—which depended solely on Arihant—to a continuous at-sea deterrence model, where at least one submarine is always available for patrol even when others undergo refit or training.

At a Glance – INS Aridhaman (S4):