What The K-4 Missile Test Means For India's Nuclear Submarine Force

India's strategic capabilities took a significant leap forward with the maiden test of its K-4 submarine-launched ballistic missile (SLBM) from an operational SSBN on 27 November.

India had previously tested the missile at least twice, launching it from an underwater pontoon.

The nuclear-capable missile, boasting a range of 3,500 km, was launched from INS Arighat, India’s second operational nuclear-powered ballistic missile submarine (SSBN), which entered service earlier this year. This development represents a major upgrade to India’s nuclear triad, providing a robust second-strike capability that deters adversaries while addressing operational constraints.

A nuclear triad refers to the ability to deliver nuclear weapons through three platforms: land-based intercontinental ballistic missiles (ICBMs), air-delivered bombs or cruise missiles, and submarine-launched ballistic missiles (SLBMs).

This diversification ensures that a nation's nuclear deterrent remains credible even if one or two legs of the triad are compromised in a preemptive strike. For India, the triad is essential to maintaining strategic stability and deterring aggression from nuclear-armed adversaries like China and Pakistan.

Until now, India’s SSBN fleet relied on the K-15 SLBM, which has a limited range of 750 km. The K-15 restricted India’s ability to strike key targets in Pakistan and China without significant risk. To overcome the missile's limited range, Indian SSBNs would need to operate in proximate waters, such as the Arabian Sea or South China Sea, exposing them to detection and counter-strike by adversary forces.

This operational advantage reduces vulnerability to anti-submarine warfare (ASW) efforts and enhances survivability, a critical factor for ensuring credible deterrence under India’s no-first-use doctrine. The K-4’s range and deployment bolster the credibility of India’s second-strike capability, which is fundamental to its nuclear doctrine of massive retaliation.

In a hypothetical scenario where China executes a counter-force strike to neutralize India’s land-based nuclear arsenal, the survival of sea-based assets becomes paramount. Equipped with K-4 SLBMs, Indian SSBNs can operate securely from bastions in the Bay of Bengal, ensuring their ability to deliver a devastating retaliatory strike.

This credible sea-based deterrent forces adversaries to account for an assured second strike, effectively deterring any first-use or counter-force misadventures by making such attacks prohibitively costly and strategically futile.

The K-4 thus strengthens the invulnerability of the sea leg, ensuring the triad's balance and the efficacy of India’s nuclear posture.

India is actively working on extending its SLBM capabilities.

The K-5, with a range of 5,000 km, is under development, promising to bridge the gap between regional and intercontinental strike capability. Simultaneously, efforts to field the K-6, a 6,000 km-range SLBM with MIRV (multiple independently targetable reentry vehicle) capability, are underway at DRDO's Advanced Naval Systems unit in Hyderabad.