India’s profitable check of the Okay-4 submarine-launched ballistic missile (SLBM) from the nuclear-powered submarine INS Arighaat marks a quiet however consequential shift within the nation’s strategic posture.
With a variety of roughly 3,500 kilometres, the Okay-4 basically modifications what India’s sea-based nuclear drive can maintain in danger, and from the place.
Put merely, Indian SSBNs can now goal most of China from patrol areas within the Bay of Bengal. That could be a dramatic enchancment over what existed till now and a significant increase to the naval leg of India’s nuclear triad, which underpins the nation’s second-strike functionality.
The check, carried out off the coast of Visakhapatnam, acquired no formal affirmation from the defence ministry. That silence is deliberate. Strategic signalling within the nuclear area usually works greatest when it’s understated.
Why the Okay-4 Adjustments the Equation
The importance of the Okay-4 check lies not merely in vary, however in geography. Till now, India’s operational sea-based deterrent relied on the Okay-15 Sagarika SLBM, which has a variety of round 750 kilometres.
That limitation imposed extreme constraints. Even when an Indian SSBN operated from the northern Bay of Bengal, it couldn’t attain China’s main inhabitants centres, industrial hubs, or strategic infrastructure, most of that are concentrated alongside the japanese seaboard.
To carry Chinese language targets in danger with the Okay-15, an Indian SSBN would have needed to enterprise dangerously near the South China Sea. That is among the most closely monitored and contested maritime areas on the earth, saturated with Chinese language anti-submarine warfare (ASW) belongings. For a platform designed to stay undetected, this was an operational contradiction.
The Okay-4 resolves this drawback. From bastions within the Bay of Bengal, waters the place the Indian Navy enjoys far higher familiarity and management, Indian SSBNs can now attain deep into the Chinese language mainland. That is the essence of a survivable sea-based deterrent.
To grasp why this issues, one should revisit the idea of the nuclear triad. A triad consists of nuclear weapons deliverable by land-based missiles, plane, and submarines. The ocean-based leg is probably the most survivable of the three. Submarines, when working covertly, are extraordinarily tough to trace and destroy. That survivability is what makes second-strike functionality credible.
Second-strike functionality refers to a state’s assured means to retaliate with nuclear weapons even after absorbing a nuclear first strike. Deterrence rests on this assurance. If an adversary believes it could possibly disarm you fully, deterrence collapses.
Inside second-strike doctrine lie two concentrating on ideas. Counter-force targets navy belongings akin to missile silos, command centres, and bases. Counter-value targets cities, industrial centres, and inhabitants hubs.
India’s declared nuclear doctrine emphasises assured retaliation fairly than war-fighting. For that, the flexibility to threaten counter-value targets credibly is essential. The Okay-4 strengthens exactly that dimension.
The SSBN Programme and What Comes Subsequent
The Okay-4 check should be seen alongside the regular maturation of India’s SSBN programme. It is a mission that has unfolded quietly over a long time, with progress measured not in bulletins however in functionality accretion.
India at the moment has two SSBNs operational. INS Arihant was commissioned into service in August 2016. Displacing round 6,000 tonnes, it’s powered by an 83 MW pressurised light-water reactor fuelled by enriched uranium. The second boat, INS Arighaat (S-3), was commissioned in end-August and retains the identical reactor and primary dimensions, however incorporates a number of technological upgrades.
The third SSBN, Aridhaman (S-4), is presently present process sea trials and is predicted to be commissioned into service subsequent yr. The primary two boats share the identical reactor design, whereas the S-4 and the follow-on S-4* characteristic an improved reactor and refinements to hull and programs design. These later boats are additionally understood to be barely bigger, providing higher endurance and payload flexibility.
In October 2025, India quietly launched its fourth SSBN, known as S-4*, into the water on the Ship Constructing Centre in Visakhapatnam. With 4 boats both operational or nearing induction, India is approaching a drive construction that permits at the least one SSBN to be on deterrent patrol always, even accounting for upkeep and refits.
Past the Arihant class, India is already trying forward. Design work is underway on a brand new technology of SSBNs, sometimes called the S-5 class. These submarines symbolize a qualitative leap.
With a displacement of round 13,500 tonnes, roughly twice that of the Arihant class, the S-5 boats are anticipated to hold as much as 12 long-range nuclear-tipped missiles. That enhance in missile load is just not about numerical parity with different powers, however about making certain ample warheads survive to ensure retaliation beneath all eventualities.
Crucially, the nuclear submarine story doesn’t finish with ballistic missile submarines. In late 2024, the Cupboard Committee on Safety accepted a significant programme to construct two indigenous nuclear-powered assault submarines (SSNs).
Whereas SSNs don’t carry nuclear weapons, their function is indispensable. Powered by nuclear reactors, they will stay submerged for prolonged durations with out surfacing, giving them unmatched endurance and attain. They’re designed to escort SSBNs and plane carriers, hunt adversary submarines, and dominate underwater areas throughout each peace and battle.
India at the moment lacks SSNs, relying as a substitute on diesel-electric submarines and restricted leasing preparations with Russia. Indigenous SSNs will permit the Indian Navy to create protected bastions for SSBN operations, significantly within the Bay of Bengal and the broader Indian Ocean. In addition they sign a shift towards sustained underwater presence fairly than episodic deployments.
India’s nuclear deterrent has at all times been conservative in posture and restrained in signalling. The Okay-4 check matches that sample. It says little, nevertheless it says sufficient. India’s sea-based deterrent is now not confined by geography, and that its second-strike functionality is steadily changing into extra survivable, extra versatile, and extra credible.
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