Following the recent commissioning of INS Aridhaman (S4) on April 3, 2026, India’s maritime nuclear capabilities are advancing rapidly toward a new era of self-reliance.
Attention is now turning to the next vessel in the lineup, the S4* (commonly known as the "S4 Star").
This fourth nuclear-powered ballistic missile submarine (SSBN) is projected to consist of nearly 90% locally sourced components, marking a massive leap in India's journey toward total independence in strategic defence manufacturing.
The pathway to building nuclear submarines locally has seen steady and impressive growth.
When the first vessel of its class, INS Arihant, joined the fleet in 2016, it featured about 70% Indian-made parts.
Its successor, INS Arighaat, commissioned in August 2024, raised that number to 75%.
With the newly inducted INS Aridhaman pushing that figure to roughly 85%, the S4* is expected to peak between 85% and 90%.
This achievement is largely powered by a robust domestic defence network, including over 200 Micro, Small, and Medium Enterprises (MSMEs) supplying everything from advanced sonar to specialized steel.
This is bolstered by vital nuclear propulsion technology mastered domestically with the help of institutions like the Bhabha Atomic Research Centre (BARC).
Unlike its predecessors, the S4* is not just an identical copy; it features a noticeably "stretched" hull. This larger physical footprint allows the submarine to carry a heavier weapons payload.
While earlier submarines primarily relied on the shorter-range K-15 missiles, the increased size of the S4* is specifically designed to accommodate the longer-range K-4 submarine-launched ballistic missiles (SLBMs).
These advanced weapons are capable of striking targets up to 3,500 kilometres away, vastly expanding the reach of the Indian Navy. Having already begun sea trials in late 2025, the S4* is scheduled to officially join the fleet around 2027.
In terms of engineering, the new submarine brings major upgrades aimed at keeping it hidden underwater.
A standout feature is the shift to an X-shaped tail rudder. This modern configuration provides much better handling and stability at low speeds, which is vital for a massive vessel trying to remain undetected in deep waters.
Furthermore, the S4* boasts a significantly quieter propulsion system. By reducing mechanical vibrations and engine noise, Indian engineers have vastly improved the submarine's acoustic stealth, bringing it closer in line with the advanced fleets of global naval powers.
Ultimately, these developments guarantee that India can maintain a constant, uninterrupted nuclear deterrent patrol at sea.
As the S4* prepares to enter service, it will heavily fortify the maritime leg of India’s nuclear triad.
The valuable lessons learned and the reliable domestic supply chains established during the creation of the S4* will also serve as a direct foundation for the upcoming, significantly larger S5-class submarines, solidifying India's position as a self-reliant maritime power.
