By N. C. Bipindra
New Delhi: India’s recent test of the 3,500-km range K-4 submarine-launched ballistic missile (SLBM) from the nuclear-powered submarine INS Arighaat may have passed with little official fanfare, but its strategic implications are profound.
Conducted in the Bay of Bengal off the coast of Visakhapatnam, the test underscores New Delhi’s steady push to strengthen the most elusive and survivable leg of its nuclear triad—sea-based deterrence, at a time of growing regional and global uncertainty.
The solid-fuelled, two-stage K-4 missile was launched from the 6,000-tonne INS Arighaat, India’s second operational SSBN (nuclear-powered ballistic missile submarine), according to defence ministry officials, who did not wish to be identified.
With a strike range of about 3,500 km and the ability to carry a nuclear payload of up to two tonnes, the K-4 significantly extends India’s undersea strike envelope.
While the defence ministry has not issued a formal statement, such silence is typical of India’s highly secretive Strategic Forces Command operations.
Crucially, the K-4 is not just another missile test; it is a capability enabler. Until now, INS Arihant, India’s first SSBN (nuclear weapon-armed submarine), has been restricted to deploying the short-range 750-km K-15 missiles.
That limitation required Indian SSBNs to patrol relatively close to adversary coastlines, increasing vulnerability. The K-4, by contrast, allows Indian submarines to strike key targets while remaining deeper in safer waters, dramatically enhancing survivability and second-strike credibility.
This test also marks the gradual transition of the K-4 from development to operational readiness. After multiple launches from submerged pontoons over the years, the missile was first tested from INS Arighaat in November last year.
The December 24, 2025, launch appears to be part of the final validation cycle, though experts note that several successful trials are usually needed before submarine-launched ballistic missiles are fully inducted.
INS Arighaat itself is central to this evolution. Commissioned on August 29 last year, the submarine represents the second step in India’s Advanced Technology Vessel (ATV) programme, a decades-old, over INR 90,000-crore effort to build an indigenous SSBN fleet.
The programme is now entering a more mature phase. India plans to commission its third SSBN, INS Aridhaman, in early 2026, followed by a fourth vessel by 2027–28. These newer submarines will be slightly larger, displacing about 7,000 tonnes compared to the 6,000-tonne displacement of Arihant and Arighaat.
Looking further ahead, India is reportedly planning a new class of much larger 13,500-tonne SSBNs equipped with more powerful 190 MW pressurised light-water reactors, a significant upgrade over the 83 MW reactors used in the first four boats.
Such submarines would offer longer endurance, higher speeds, and the ability to carry more missiles with greater range.
Despite these advances, India still lags far behind the United States, Russia, and China in terms of SSBN size, missile range and numbers. However, the operational deployment of the K-4, followed in the future by longer-range K-5 and K-6 SLBMs in the 5,000–6,000 km class, will help narrow this gap.
While these systems do not match intercontinental ballistic missiles (ICBMs) fielded by major nuclear powers, they are sufficient to hold regional adversaries at risk.
Importantly, India’s nuclear deterrent is already strong on land and in the air. The Agni-5 ballistic missile offers a strike range exceeding 5,000 km, while aircraft such as the Rafale, Su-30MKI, and Mirage-2000 are capable of delivering nuclear gravity bombs.
Yet SSBNs remain the crown jewel of nuclear deterrence. Hidden beneath the oceans, they are considered the most secure and survivable platforms for assured retaliation.
In that sense, the K-4 test from INS Arighaat sends a clear but quiet message: India’s “no first-use” policy is backed by a steadily improving ability to retaliate decisively, even after absorbing a first strike.
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